What These Processes Need: The Negative, the Paper and the Light

Three things decide a print in this cluster, and all three are settled before you open a bottle. The negative has to hold a much longer density range than anything you have printed so far. The paper has to be the one kind of fine art paper that every conservation standard of the last thirty years tells you not to buy. And the light has to be ultraviolet, delivered as a measured dose rather than a remembered number of minutes.

None of that is preference. Each is arithmetic, and the arithmetic is published. This page assembles it, says where it came from, and says plainly where the published figures disagree with one another — because they do, by a factor of nearly two in the case of platinum, and a reader who has only met one of the numbers will mis-make their negatives for a year.

The exposure scale problem, in numbers

Part XIII established the number that joins a negative to a paper. A paper’s log exposure range is the span of log exposure between the point where useful density begins and the point where it stops rising; ILFORD publish it multiplied by a hundred as ISO Range (R), measured to ISO 6846:1992 and stated for the image as projected on the enlarger baseboard. On the current MULTIGRADE RC DELUXE, filter 2 gives R90 — a range of 0.90 — and the softest filter, 00, gives R160.

Two things change when you leave the enlarger.

First, the process’s scale is fixed when you choose the formulation. There is no filter drawer. The only lever left is the development bath of the modern oxalate sensitisers, which the variants lesson deals with, and it moves things by a few tenths, not by a grade. Ware’s rule is blunt: the contrast of the negative is adapted to the process, never the reverse.

Second, the negative’s density range and the process’s exposure scale are the same number. In contact printing there is no Callier effect, because no lens collects a selected cone of the transmitted light — the paper receives everything the negative passes. So the scattering that makes a silver negative print harder in a condenser enlarger than in a diffuser one simply does not arise, and Ware states the consequence directly: the ultraviolet density range required in the negative should equal the logarithmic exposure scale of the sensitiser. That equality is what makes the table below usable at all.

Exposure scales on one log-exposure axis

1. 1The dashed line at 0.90 — the exposure scale of a grade 2 enlarging paper, and roughly the density range of the negatives already in your file
2. 2Solid bar — the lower published figure
3. 3Hatched extension — the upper published figure, where the source gives a range rather than a number

Every figure is quoted in the table below with its source and its measurement condition. The bars are drawn from those figures; they are not measured curves, and the vertical order carries no meaning beyond grouping the two enlarging-paper rows at the top.

The published figures, and their conditions

Every number here is quoted, not derived. The last column is the point of the table: a figure means nothing until you know what instrument produced it and through what filter, and three of these rows do not say.

Material or process	Figure	Source	Measurement condition
MULTIGRADE RC DELUXE, filter 2	0.90	ILFORD technical information	ISO 6846:1992, image projected on the baseboard, read with a photometer — visible light
MULTIGRADE RC DELUXE, filter 0	1.30	ILFORD technical information	as above
Classic cyanotype	exposure scale about 0.9; density range 0.9 to 1.2	Ware, Cyanomicon 7.2.3 and 6.5	stated as UVA density range; contact printing, no Callier effect
Cyanotype, Photographers’ Formulary standard sensitiser	expressed as “a negative that gives a good print on grade 0 paper” — about 1.3 on the ILFORD scale	Photographers’ Formulary kit instructions	not stated
New Cyanotype	1.6 to 2.4; about 2.1 to 2.4 after acid development, about 2.6 developed in water	Ware, Cyanomicon 6.5, 7.3.8, 7.3.9	UVA
Simple Cyanotype	2.7, 2.3 or 1.8 by sensitiser formula; about 1.3 if the acid bath is omitted	Ware, Simple Cyanotype	UVA; Dmax about 1.5
Kallitype	about log 1.8	Sandy King	not stated
Kallitype, Photographers’ Formulary kit	up to 1.85	kit instructions	not stated
Van Dyke Brown, Photographers’ Formulary kit	up to 1.85	kit instructions	not stated
Platinum, print-out (Malde-Ware)	1.5 at 32 and 55 % RH, 1.8 at 80 % RH	Ware, Platinomicon Table 7.1	Δ log H from fog + 0.04 to 0.9 Dmax, reflectance, X-Rite 312
Palladium, print-out (Malde-Ware)	2.0, 2.2 and 2.4 at 32, 55 and 80 % RH	Ware, Platinomicon Table 7.1	as above
Platinum, traditional development	about 2.0, unmodified by chlorate	Ware, Platinomicon 6.5	not separately stated
Platinum, Photographers’ Formulary kit	1.0 to 1.5	kit instructions	not stated
Palladium, Photographers’ Formulary kit	1.3 to 1.5	kit instructions	not stated
Salted paper and albumen	no figure published	Reilly	see below

Reilly is the honest outlier and deserves reading rather than skipping. He states outright that because the nature and amount of binder varies so much, no exact density ranges can be specified for negatives intended for salted, arrowroot and albumen papers, and gives a measurement instead of a number: sensitise a sample sheet, print a 21-step grey scale to full maximum density, count the steps you can still tell apart, and the density difference across those steps is your negative’s target. He records Hübl’s finding that glossy albumen came out equal to platinum paper and that salted papers exceeded platinum “by a considerable margin”, and orders the family — plain salted longest, matte albumen and arrowroot next, glossy albumen shortest — because a glossy binder suppresses the diffuse scattering that makes a matte black look grey.

⁇Where the sources disagree, and how much

Platinum and palladium. Photographers’ Formulary put the negative’s density range at 1.0 to 1.5 for platinum and 1.3 to 1.5 for palladium. Ware’s measured exposure ranges are 1.5 to 1.8 for platinum and 2.0 to 2.4 for palladium. At the extremes that is a factor of more than two in exposure — three stops.

The course’s reading, offered as interpretation and not as fact: these are two different processes wearing one name. The kit is the traditional development platinotype, whose contrast is truncated on purpose by drop-counted potassium chlorate — Ware says explicitly that the chlorate system became standard practice among users whose negatives have insufficient density range, and that its effect is to reoxidise part of the iron(II) photoproduct and so shorten the scale. Ware’s figures are for the print-out Malde-Ware sensitiser at controlled humidity with no contrast agent at all. Both numbers are right for their own process. Neither is right for the other.

Classic cyanotype. Ware gives about 0.9 to 1.2 and equates it with a negative made for grade 3 paper. Photographers’ Formulary tell you that a negative printing well on grade 0 suits their standard sensitiser, which is a claim of about 1.3, and offer a higher-contrast sensitiser for grade 1 and 2 negatives. The course states Ware’s figure, because it is given as a measured exposure scale in a work that publishes the characteristic curves, and records the kit maker’s as a supplier’s practical guidance that points a quarter of a log unit softer. If your classic cyanotypes are flat, that quarter of a unit is the first thing to suspect.

Why a grade 2 negative gives an empty print

Put a negative of density range 0.90 in front of a New Cyanotype whose exposure scale is 2.2, and the negative controls only 0.90 of the 2.2 log units the process can span. The rest of the scale is not reached: the clear film base delivers so much light that the shadows go to maximum blue, the densest highlight is nowhere near enough to hold back the paper white, and the whole picture lands compressed into the bottom third of the process’s range. It is not that the print is contrasty. It is that the print is flat and dark at once: a small tonal excursion, sitting low, with nothing anywhere near the paper white and nothing separating the deep tones from one another.

Turn it round and the same arithmetic explains why a negative made for palladium will not print on a classic cyanotype: 2.4 log units of negative laid on a process that spans 0.9 gives you a picture built entirely from the negative’s middle, with the highlights blank and the shadows blocked.

Three routes to a negative that fits

Nobody recommends one of these. Each buys the density range with something different.

Develop the film further

The cheapest route, and it changes nothing about your camera work. Ware’s instruction is to give a continuous-tone camera film normal exposure and develop it 75 to 100 per cent longer than the time recommended for silver-gelatin enlargement printing, aiming at a contrast index in the range 0.7 to 1.3 depending on subject and interpretation. Sandy King’s figure for kallitype is compatible and a little gentler: about 50 per cent longer than normal for a grade 2 paper.

Part XIII’s lesson on gamma and contrast index gives you the machinery to hit those numbers deliberately rather than by trial, and the film maker’s published curves of contrast index against development time are the map. What it costs: grain, because extended development amplifies it; highlight separation, which starts to run up the shoulder; and the negative itself, because Ware is explicit that contrast indices in that range are more or less incompatible with normal silver printing. One negative cannot serve both. His own compromise is to expose and develop normally for silver, ensuring plenty of shadow detail, and make a higher-contrast internegative from that — a route he keeps in print while noting that much of what he wrote about it has become obsolete as the duplicating and gravure films it named ceased to be manufactured. Treat the internegative as a route that needs materials you must confirm still exist before you plan around it.

Use a staining developer

A pyro developer leaves a yellow-green stain proportional to the silver, and that stain is opaque in the blue and near ultraviolet where these processes work while being nearly invisible in green. The effect is a negative with a modest visual density range and a much longer printing range at 365 nm. The course’s three staining developers — PMK, Pyrocat-HD and 510-Pyro — are all in the formulary with their provenance and their mechanism, and Bostick & Sullivan name pyro developers alongside D-19 as what to develop a platinum negative in.

What it costs is your ability to measure what you have made. That is the next section, and in this course’s view it is the most under-stated difficulty in the whole cluster.

Print a digital negative

An inkjet negative on transparency film has one large advantage that Sandy King states plainly: every negative you make comes out at close to the same density and contrast range, so exposure and contrast become consistent across a body of work in a way that camera negatives never are. It is also the only route that lets you set the density range to a number you choose rather than to the number your development happened to give.

What it costs is a calibration you have to do once for every combination of printer, ink set, driver setting and film — and redo when any one of them changes.

The digital negative is a calibration, not a setting

Ware’s workflow is worth teaching because it is printer-agnostic by construction. It never tells you an ink density, a curve or a driver setting, because those are properties of a machine the author does not have. It tells you how to find yours. The course can publish it for exactly that reason, and cannot publish anything about your printer.

The procedure, in the order it happens:

1. Print a 100-step tablet on the film you will use for everything, at intervals of 1 per cent relative opacity, using the identical driver settings and materials as your real negatives — matt black ink where the driver offers a choice, and the maximum-ink-density control noted down before you print. Let it cure overnight; Ware records that inks change density with time.
2. Assemble the standard printing setup — light source, distance, coating, wet processing — and hold everything constant from here on.
3. Make a trial print and overexpose it deliberately, until the shadow steps block up and become indistinguishable. Note that exposure as E. Overexposure here is judged the negative-worker’s way, by shadows blocking, not the digital way by highlights blowing out.
4. Find the first step, from the bottom, that is just perceptibly separated from the one above it. Its transmittance is P, in per cent.
5. Compute the Standard Printing Exposure.

SPE = E × P ÷ 100

Standard Printing Exposure

E is the exposure that overexposed the test print, in whatever unit your source is controlled by — minutes, seconds, or the arbitrary units of a light integrator. P is the transmittance, in per cent, of the lowest negative step that still shows tonal separation in that print. The SPE is the exposure that puts the clear film base just below the process’s maximum density, and it then applies to every print you make with those negatives under that setup.

6. Print the step tablet at the SPE and find the step that prints “just white”. The aim is the 99 per cent opacity step; within 2 or 3 per cent of it is satisfactory. If several steps print white the negative is laying down too much ink; if none does, too little.
7. Change the driver’s maximum ink density and go back to step 1. This is the loop, and it is the whole calibration: you are adjusting the ink’s ultraviolet density range until it equals the exposure scale of the process.
8. Set the mid-tones with the gamma slider, not with a curve. Ware’s finding is that raising gamma in the positive image to about 1.8 to 2.4 before inversion serves as a generic tone-correction curve, and that it agrees in practice with the personalised curves other workers have plotted point-by-point from step-tablet prints for platinum-palladium. The positive will look grossly overexposed on screen. That is expected.

!What the course can and cannot claim here

Can: that the calibration loop above is published by a Tier 2 conservation source and is defined entirely in terms of your own equipment, and that the four things which force a recalibration are the printer model, the ink set, the driver settings and the film substrate.

Cannot: anything about a particular printer, ink or film. Ware names Pictorico OHP and PermaJet Digital Transfer Film as the ceramic-coated transparency materials he used, and Photoshop CS on an iMac as the software — a specification dated by its own text. The course repeats those as what the source says, not as a recommendation, and publishes no ink density, no driver setting and no curve. If a page anywhere gives you a numeric curve for “cyanotype”, ask which printer it was measured on.

One consequence worth stating. Placing the effective maximum density higher spends more of the 256 available levels on separating the shadows and leaves fewer for everything above, which compresses the rest of the picture. And if you chase a maximum black by stretching the SPE too far, the inks may simply lack the ultraviolet blocking opacity to give a paper-base white at all. The SPE is a choice with a cost, not a constant.

Ultraviolet density is not visual density

This is where a great deal of alternative-process advice quietly falls apart, and the course would rather say so than pretend.

A densitometer reports the density of a specimen under the spectral condition of that instrument — the product, wavelength by wavelength, of its source, its filters and its detector. Part XV’s lesson on geometry and spectral response establishes that in full. Read a negative in green and you have a number that predicts what an enlarger will do with it. Read the same negative at 365 nm and you may get a very different number, because:

• Film base is often not transparent in the near ultraviolet even when it looks water-clear. X-Rite sell the separate ultraviolet response of the 361T as a feature on precisely this ground — that it measures film-base fog an ordinary densitometer cannot see.
• A pyro stain is a large density in blue and a small one in green, so a stained negative measured visually understates its own printing density by an amount nobody has published.
• An inkjet negative is built from dyes or pigments chosen for a completely different purpose, and its ultraviolet transmission is not predicted by its appearance at all. Ware’s own conclusion, stated in the Platinomicon, is that with inkjet internegatives optical densitometry is of little value and the correct density range is arrived at empirically — which is why his workflow calibrates by printing rather than by measuring.

📓What your Part XV densitometer can honestly do here

The instrument you build in Part XV has a green LED near the photopic peak and a bare silicon photodiode, with a blue LED offered as a second channel. It has no ultraviolet channel. The optical head page describes a UV variant and deliberately does not build it: a 365 nm source is a hazard class of its own, needing an enclosure and an interlock, and it belongs with this cluster rather than smuggled into a Level A afternoon.

So: your densitometer can measure a visual density range, and that is a real and useful measurement for a plain silver negative developed in a non-staining developer, where the image is neutral and the green reading tracks the ultraviolet one closely enough to plan by. It cannot measure the printing density of a stained negative or of an inkjet negative, and the course publishes no conversion factor for either, because no number in its corpus supports one.

What you do instead is what Ware does: calibrate by printing. A step tablet, the Standard Printing Exposure, and the count of steps between the last one that prints maximum density and the first that prints paper white. Ware gives the arithmetic for the Stouffer T3110, whose steps are 0.1 apart: the exposure scale is the difference between those two step numbers divided by ten. That is a real measurement of the thing you actually care about, made with the process as its own instrument, and it is available to a reader who owns no densitometer at all.

Record, always: the instrument, its spectral condition, its geometry, and whether the figure is visual, ultraviolet or a step count. A density with no condition attached is not data.

The paper, and what “acid free” costs you

Every paper you have been taught to prefer is the wrong paper here, and the reason is arithmetic rather than taste.

Papermaking changed. Ware quotes the paper chemist John C. Roberts of UMIST: from around 1840 to the early 1970s paper was usually made in an acidic environment at pH 4 to 5, because rosin and aluminium sulfate were used for sizing; since the early 1970s the industry has moved to neutral and slightly alkaline systems for lower corrosion, better fibre swelling, higher filler loadings and cheaper drying. On top of that came two standards. ISO 9706:1994 for permanent paper requires a pH between 7.5 and 10.0 and an alkali reserve of at least 0.4 moles of acid per kilogram, which is at least 2 per cent w/w calcium carbonate. ISO 11108:1996 for archival paper adds a cotton, linter, hemp or flax furnish and greater folding endurance, and requires everything ISO 9706 requires.

A paper advertised as “acid free” is therefore, in all probability, a paper with chalk in it.

🧮The eightfold excess

Ware’s calculation, reproduced with its assumptions visible.

Take a sheet of 250 g/m². Per square metre that is 0.25 kg, so the alkaline reserve is

0.25 kg × 0.4 mol/kg = 0.10 mol of hydroxide equivalent per square metre.

Now coat it. A typical siderotype coating is 25 cm³/m² of a sensitiser about 0.5 mol/L in iron(III), so

0.025 L × 0.5 mol/L = 0.0125 mol of iron(III) per square metre.

0.10 ÷ 0.0125 = 8. The paper carries an eightfold molar excess of alkali over the iron you have just put on it.

Ware adds the qualification that matters: the chalk is involatile and will not migrate through a dry sheet, so the damage happens in the wet state, area for area, and only a fraction of that reserve ever has to reach the iron for the excess to be decisive.

The alkali does two separate things, at two different times.

Before the exposure it destroys the sensitiser. Hydroxide hydrolyses the iron(III) complex out of existence, precipitating hydrous iron(III) oxide, and with an oxalate sensitiser the calcium precipitates insoluble calcium oxalate as well — which Ware notes is the same substance as some kidney stones, and which leaves a gritty texture in the sheet.

Fe³⁺ + 3 OH⁻ → Fe(OH)₃

Hydrolysis: what the paper's alkaline reserve does to the iron(III) before any light falls on it

Ca²⁺ + C₂O₄²⁻ → CaC₂O₄

And with an oxalate sensitiser, an insoluble calcium salt in the fibres as well

After the exposure it destroys the picture. Holtzman found that a buffer at pH 9.4 completely decolourises Prussian blue by irreversible hydrolysis in one to ten minutes, and pH 9.4 is the pH of a saturated solution of calcium carbonate. The mechanism belongs to the chemistry lesson, which writes the reaction out. Ware’s own worst-case test is the memorable one: processed cyanotypes of all five sensitisers, partly coated with a chalk paste and held above 95 per cent relative humidity, lost serious density within 48 hours.

Why the same buffer is right for a silver gelatin print

This is the tension worth holding in your head, because the two halves of the course now give opposite advice and both are correct.

The Image Permanence Institute’s guide to ISO 18902 sets out what “photo-safe” means for storage, display and labelling materials: they must pass the Photographic Activity Test of ISO 18916, they must be lignin-free, and paper-based materials must include an alkali reserve of at least 2 per cent calcium carbonate. The reason is that a silver gelatin print’s enemies are acid hydrolysis of the cellulose support, which embrittles it, and oxidising and reducing species that fade the image and cause silver mirroring. A reservoir of chalk neutralises acids arriving from the air, from the mount, or from residual processing chemistry, and it protects the picture by protecting the paper.

Note what the same standard does at the other end: it puts an upper pH limit of 10, because a highly alkaline environment weakens a gelatin binder. Even for silver, the buffer is a compromise with a ceiling.

For a cyanotype there is no compromise to strike, because the image substance itself is the thing the alkali attacks. Ware’s conclusion for conservators is unusually direct: cyanotypes are destroyed by mild alkali at pH 8 to 10 far more rapidly than cellulose is destroyed by correspondingly mild acid at pH 6 to 4, so the conservator should be prepared to subordinate the interests of the paper to the interests of the image. Deacidification of a cyanotype is out of the question. So is a buffered mount, a buffered interleaf and an alkaline adhesive on the verso — the last because hydroxide can migrate through plain paper.

One image, one enemy, opposite prescriptions. That is not an inconsistency in the standards; it is what happens when a rule written for one image substance is applied to another.

Sizing, surface and absorbency

Sizing is what stops the sheet behaving like blotting paper, and where it sits decides where your sensitiser sits.

Internal (engine) sizing is added to the pulp before the sheet forms. The modern agent is alkyl ketene dimer, sold as Aquapel and its equivalents: a molecule with a long hydrophobic hydrocarbon tail and a reactive head that bonds to the glycosidic hydroxyl groups of the cellulose, converting them to a cellulose alkyl β-keto ester and making the fibres themselves water-repellent. The older alum-rosin system precipitates hydrophobic abietic acid within the fibres, using potassium alum both as the acidifier and as a mordant. Ware’s verdict on both is the same: papers internally sized with alum-rosin or AKD seem perfectly compatible with the processes.

Surface sizing is applied to the formed sheet, usually by immersion in gelatin or starch, and it is where the objections live.

• Gelatin binds strongly to platinum(II) in aqueous solution, and the resulting amino-acid complex is less readily reduced to the metal by the iron(II) photoproduct. Ware’s rule: avoid gelatin-sized papers if the sensitiser contains a significant proportion of platinum. The problem does not arise with the more reactive palladium, which is why practitioners who work mostly in palladium can recommend gelatin sizing in good faith and be describing a real experience that does not generalise.
• Starch, in mill practice, means oxidised starch — starch treated with hydrogen peroxide or hypochlorite, which leaves carboxylate groups on the chain. Carboxylates bind iron(III); that is precisely what they are doing in the ferrioxalates and ferricitrates of your sensitiser. The consequences Ware lists are a less efficient sensitiser, a shortened exposure scale, and possible sequestration of iron(III) that eventually stains. He concludes that no good purpose is served by starch-sizing a paper intended for siderotype.
• Hardening agents in a size are often reductants. Aldehydes such as formaldehyde and glutaraldehyde, and the sulfites used in pulp treatment, are named in Ware’s hypothesis for the randomly distributed black specks that appear in some platinum and palladium prints: they reduce iron(III) to insoluble iron(II) oxalate microcrystals in the coating, invisible in a yellow layer until the developer solubilises them onto the noble metal. Marked as hypothesis, because that is how he marks it.

Surface, and where the sensitiser ends up

Hot pressed is what both of Ware’s specifications ask for — smooth, or heavily cold-pressed and calendered. “Not” and “Rough” surfaces are difficult to coat evenly and lose resolution in contact printing, because the negative cannot lie against a hill and a valley at once. The trap is that some heavily calendered commercial papers do not stay smooth: they swell and roughen perceptibly on wet processing, and a paper chosen dry can be a different paper by the time the print is washed.

The deeper question is where the sensitiser goes, and Ware’s statement of it in Simple Cyanotype is the sentence to remember: the success of cyanotype depends on the sensitiser penetrating the interfibrillar space of the surface cellulose fibres, where the pigment will be trapped, and not simply remaining in the coarse pores of the paper, from which it washes out.

Two consequences follow directly.

Maximum density. Pigment that formed in a pore, unanchored, leaves during the wash. That is a straight loss of Dmax, and it is why the classic cyanotype is traditionally over-exposed by two or three stops to compensate — the loss is real, and the compensation is paying for it twice.

Sharpness. Pigment that sank into the body of the sheet is imaging at a depth, so every edge is softened by the thickness of paper above it. Both problems have the same fix — get the solution into the surface fibres and no further — and it is why the coating technique in the coating and printing lab makes the first two rod passes fast and the last three as slow as possible, and why a non-ionic surfactant is added to some sensitisers to help penetration of exactly that surface layer.

Weight follows the print size and the wet handling rather than the chemistry: 160 g/m² is adequate to A4 or 10 × 8, and 240 g/m² or more at A3, to limit the cockling and bellying that hydroexpansion of the wetted area sets up. A sheet that bellies does not contact the negative, and a sheet that does not contact the negative is not making a sharp print whatever else you have got right. Very heavy papers wash slowly, which is its own cost.

The one that surprises everybody: porosity

The photochemistry of every siderotype releases carbon dioxide — it is the decarboxylation of the ligand, established in the chemistry lesson. That gas has to go somewhere, and the only route out is backwards, through the sheet and into the backing.

If the paper is too impermeable, or the backing is a rubber or plastic sheet rather than felt, the gas forms a bubble layer between the sensitised surface and the negative. A gap between negative and paper blurs the image, and the amount of blur depends on the geometry of the source, as the next section sets out. Ware records the observation directly: bubbles that visibly blur a print under a bank of fluorescent tubes may not show at all under a near point source such as the sun. China clay fillers, which give a paper that extremely smooth and shiny look, block the pores; so does gelatin surface sizing.

So “porous enough to breathe” joins the specification, and the felt blanket behind the paper in the printing frame is not padding. It is a gas absorber.

The additives that ruin prints

Ware publishes a summary specification for siderotype paper, dated November 2020, and it is easier to read as a list of prohibitions.

Not wanted	Why
Alkaline buffer — chalk or any other alkali	Hydrolyses the iron(III); destroys Prussian blue at pH 9
Clay filler or aluminosilicate	Blocks the pores the carbon dioxide must escape through
Retention aids — cationic polyacrylamide, cationic starch	Trap the sensitiser’s anions; blotching (below)
Wet strength aids such as Kymene polyamidoamine-epichlorohydrin resin	Named in the specification; mechanism not stated
Optical brightening agents	Fluoresce in the band the process prints by; archival stability questioned
Dyes and white pigments, notably titanium dioxide	Titanium dioxide is photoreactive
Residual bleach	A reductant or oxidant left in the sheet, reacting with the sensitiser
Surface sizing — gelatin or oxidised starch	Binds platinum(II) or iron(III); shortens the exposure scale
Aldehyde hardening agents	Reductants; implicated in black specks
Mixed furnish	Absorbs sensitiser unevenly: granularity and blotchiness

The furnish that is wanted is nearly 100 per cent alpha-cellulose, long-fibre cotton or linen but not the two mixed, on a wove mould rather than laid, with the watermark outside the picture area.

Blotching, and a hypothesis marked as one

The most interesting entry on that list is the one that did not exist before the 1980s. Flocculation of the fibre during sheet formation shows up in siderotype prints as woolly, cloudy, lighter patches — Ware calls it blotching — and it is absent from the historical literature. His diagnosis is that mills now add retention aids at the wet end to improve the trapping of fines, and that these high-molecular-weight cationic polyelectrolytes carry quaternary alkylammonium cations which attract and immobilise exactly the small mobile anions the sensitiser chemistry runs on: the trisoxalato- and dioxalatoferrate ions, hexacyanoferrate(III), and the tetrachloro complexes of platinum(II) and palladium(II).

The hypothesis explains a real pattern. It predicts that the traditional formulations should escape, because their sensitisers — ferric ammonium citrate and ferric oxalate as made up in the classic recipes — are oligomeric and carry little ionic charge, and Ware observes that classic cyanotype and development platinotype do not generally suffer from blotching. It predicts that a large excess of some other mobile anion should suppress it, and the Malde-Ware print-out platinum-palladium sensitisers formulated with 17 per cent w/v ammonium nitrate are observed to be far less susceptible than the version without it.

And it is still a hypothesis, which Ware says himself: the crucial test would be to establish that retention aids are always present in the afflicted papers, and papermakers do not disclose what is in their products. What he has instead is a review stating that hardly a single mill in Central, Western or Southern Europe does not use retention aids, and one craft papermaker’s personal assurance that his Buxton and Herschel sheets never contained them and never blotched. That is proof by absence, offered as such. The course records it the same way.

The tests you can do before committing a box

🧪Four tests, with what each one actually detects

1. The coated-strip test, which is the good one. Ware states that the New Cyanotype sensitiser is itself a sensitive test of paper quality: coat a strip, leave it in the dark at normal humidity for some hours, and look at it. The coated side should stay light yellow. A shift towards green — or worse, blue — is chemical fogging, and signals impurities or additives hostile to this process and probably to the other siderotypes as well. This is the only test on this list that tests the thing you care about rather than a proxy for it, and it costs one strip of paper. Run it on every new paper and on every new batch of a paper you already use, because Ware’s other warning is that a maker can change a furnish without notice.

2. Lugol’s solution, for starch. Five per cent w/v iodine with 10 per cent w/v potassium iodide in water; a blue-black colour indicates starch. This is the test Sarah Wagner ran at the National Gallery of Art on Willis’s Platinotype papers, and it found starch in the KK, AA and Japine stocks. It detects starch, and only starch — it says nothing about gelatin, AKD, chalk or retention aids, and a negative result rules out one item on a list of ten.

3. An ultraviolet lamp, for optical brighteners. Optical brightening agents work by absorbing ultraviolet and re-emitting it as visible blue, so a brightened sheet held under a UVA lamp glows noticeably beside an unbrightened one. The course could not source a published method or acceptance criterion for this as a paper test, and prints it as a comparative observation rather than a test: compare against a sheet you already know is unbrightened, in a dark room, and treat “brighter than the reference” as a reason to ask the maker rather than as a measurement. What is established is the prohibition, not the assay.

4. Surface pH, with a real caveat. The pH figure a paper maker quotes, and the one the standards use, comes from a cold extraction method: the paper is macerated in water and the extract measured. A surface-pH pen or a spot of indicator on the sheet is not that measurement, and it reports the surface rather than the reserve. A paper can read close to neutral at the surface and still carry 2 per cent chalk through its body, which is the quantity the arithmetic above says will overwhelm your sensitiser. Use the quoted pH as a screen — Ware wants it below 7 — and use test 1 as the verdict.

The test the course does not publish. The obvious spot test for iron contamination in a sheet is a drop of acidified hexacyanoferrate solution, which would give Prussian blue where iron is present. No published version of that test as a paper assay, with a detection limit or a validation, was found in this course’s corpus, so it is not printed here as a method. What the corpus does establish is that metal impurity is real and detectable by instrument: an electron-microprobe analysis of Willis’s KK paper listed copper among the elements found, and Ware’s own suggested origin for it — brass from the blades of a Hollander beater — carries his question mark.

Pre-treatment, and when to buy a different paper instead

If the paper you have is buffered, the chalk can be destroyed before coating. Two sources, two slightly different recipes, and the course prints both rather than averaging them:

• Cyanomicon 7.3.5: 5 per cent v/v hydrochloric acid, or 5 to 10 per cent w/v sulfamic acid, for about 10 minutes, then washed.
• Platinomicon 8.5: 1 to 2 per cent v/v hydrochloric acid, or 5 to 10 per cent w/v sulfamic acid, for 10 to 20 minutes.

CaCO₃ + 2 H⁺ → Ca²⁺ + H₂O + CO₂

Decalcification: the chalk leaves as carbon dioxide and a soluble calcium salt

Oxalic acid is the wrong acid, and it is the one practitioners reach for. Calcium oxalate is as insoluble as the calcium carbonate it is meant to replace, so the treatment converts one gritty insoluble calcium salt into another and achieves nothing.

Ware’s own assessment of the whole procedure is not enthusiastic: he calls it tedious and undesirable, notes that it tends to degrade the paper surface and strength, and in the Platinomicon calls it unnecessary. He also offers a possible hidden benefit, again as a suggestion: the small chloride or sulfamate anions left behind may neutralise the cationic retention aids that are present unacknowledged, and so proof the sheet against blotching as well.

Student-applied sizing is the other pre-treatment, and here the course is deliberately thin. A gelatin size will hurt a platinum print and may cost a palladium one nothing; a starch size, in the form the mills use, will shorten your exposure scale. Photographers’ Formulary publish an arrowroot starch sizing procedure with their cyanotype kit, and it is theirs rather than the course’s; nothing in the corpus establishes that a home-applied size improves a modern unbuffered siderotype paper, so no sizing procedure is published here.

When pre-treatment is a fix and when it is denial. Acidifying a buffered sheet addresses one item on the prohibition list. It does nothing about retention aids, clay fillers, optical brighteners, titanium dioxide, wet-strength resin, oxidised starch surface size or aldehyde hardeners, and those are eight of the ten. If the coated-strip test greens on a paper you have already decalcified, the answer is a different paper.

Ware names the ones made without chalk: Arches Platine, Bergger COT 320 and COT 160, Hahnemühle Platinum Rag, Legion Revere, Wyndstone Vellum, Awagami Masa, Atlantis Silversafe Photostore, and the handmade Buxton and Herschel sheets from Ruscombe Mill. Bergger’s own datasheet, dated June 2020, names COT 320 and COT 160 as uniquely suitable for its cyanotype kit.

!A dated list, and an unverified one

Those names come from Cyanomicon as revised in 2020 and from a manufacturer’s datasheet of the same year. The course was unable to verify current UK availability or current published specifications for any of them. Papers are reformulated, renamed and discontinued, and Ware’s own warning is that a maker may change a furnish from batch to batch without notice.

Treat the list as a starting point for a search, not as a shopping list, and confirm two things from the current published specification before you buy a box: 100 per cent cotton or linen, and no alkaline buffer. Then run the coated-strip test on the first sheet anyway. The planner carries the course’s dated price data, and hot-pressed cotton paper is among the items it lists as gaps, with no UK supplier listing yet recorded against it.

Humidity, as a variable you record

Humidity is the variable most likely to be left out of a notebook and most likely to explain a result, and its importance differs sharply across this cluster.

For cyanotype it barely matters. Ware’s statement is flat: the prevailing relative humidity has very little effect on the results of printing in cyanotype — but it can profoundly affect some of the other iron-based processes.

For print-out platinum and palladium it is a contrast control. Ware’s Table 7.1 gives the exposure range of the Malde-Ware sensitisers against relative humidity, measured as Δ log H from fog + 0.04 to 0.9 Dmax on an X-Rite 312 in reflectance mode, with the standing caveat that the parameters vary with the paper.

Sensitiser	32 % RH	55 % RH	80 % RH
Platinum	1.5	1.5	1.8
Palladium	2.0	2.2	2.4
Platinum–palladium 3:1	1.6	2.0	2.2
Platinum–palladium 1:1	1.6	1.8	2.0

Two things are worth reading out of it. The scale lengthens with humidity in every column, so damp paper prints softer. And the speeds move in opposite directions — platinum loses speed as humidity rises while palladium gains it — which is why a 3:1 mixture is nearly humidity-independent in speed and is what Ware recommends for stable working. His optimum band is 50 to 80 per cent: below 50 per cent there is only partial print-out and considerable development, and above 80 per cent the maximum density weakens because the sensitiser diffuses too deeply into the paper.

For the New Cyanotype the humidity variable is expressed as drying. Ware’s measurements, on Buxton paper with Stouffer T3110 tablets, are worth having as a warning against fiddling:

• Heat drying the coated sheet at 42 °C for five minutes shortens the tonal scale by about one stop, from 2.3 to 2.0, and may coarsen the texture slightly.
• “Darktime” — leaving the exposed print 19 hours in the dark at 58 per cent RH and about 20 °C before wet processing — lengthens it from 2.3 to 2.6, but weakens the maximum density, flattens the shadows and causes edge fog at the tideline.
• Doing both returns you to about 2.3 with a loss of Dmax, which is Ware’s own conclusion: it is best to do neither.

Controlling it, and recording it

If you need a humidity rather than merely a record of one, the method is a sealed box over a saturated salt solution, with excess solid salt present so the solution stays saturated. Ware’s three: ammonium chloride at 80 per cent RH, sodium chloride at 76 per cent, and calcium nitrate tetrahydrate at 56 per cent. Half an hour is the minimum for evenness; a few hours is the upper limit. Pure water gives 100 per cent RH and turns the timing critical — 5 to 20 minutes for a warm tone, 30 to 40 for fuller print-out and a colder one, and more than an hour weakens the image and causes clearing problems.

At the other end, sensitised platinum paper is stored below 10 per cent RH over silica gel or anhydrous calcium chloride to inhibit the decomposition reactions, which Ware says keeps it six months without loss of quality — a direct descendant of Willis marketing his Platinotype paper in tins with a desiccant.

📓What goes in the record

• Relative humidity and temperature at coating, at drying, and at exposure. Three readings, not one.
• How long the sheet equilibrated. Ware allows at least an hour for paper to come to equilibrium with the room, and at least half an hour in a humidifying tank.
• How it was dried: room temperature and for how long, or an air stream and at what temperature.
• The gap between coating and exposure. Cyanotype sensitiser is used within a few hours of coating if possible; the storage life depends on the purity of the paper base.

None of that is bureaucracy. Two prints that differ by a stop of contrast and by nothing you wrote down are two prints you cannot learn from.

Coating: rod against brush, and what it costs per print

The coating rod is a thick-walled glass tube bent into a flattened U — a bicycle-handlebar shape, 6 to 12 mm across, with the straight centre as wide as the coating area. The brush is a broad Japanese hake, and it must have no metal ferrule.

Ware’s judgement is that the rod is the more economic implement and the brush the more painterly, and that the difference “is of little consequence with an inexpensive sensitizer like cyanotype [but] is a serious disadvantage when one comes to coat platinotype.” That is worth a number.

Specific coating volume

The useful unit is cubic centimetres of sensitiser per square metre of paper, and it varies with the paper’s absorptivity and its sizing as well as with the implement.

Method and source	Specific coating volume	How it was obtained
Rod — Ware, Platinomicon 6.10	24 to 36 cm³/m², about 30 typical	stated directly, for typical papers
Rod — Ware, Cyanomicon 7.1.3 and Simple Cyanotype	about 1.5 cm³ per 10 × 8 in, ≈ 29 cm³/m²	course’s arithmetic from the stated volume and area
Brush — Bergger cyanotype datasheet	5 mL + 5 mL coats about five 8 × 10 sheets, ≈ 39 cm³/m²	course’s arithmetic from the maker’s own worked example
Brush — B&S salted paper, per coat	40 drops for an 8 × 10 image ≈ 2 cm³, ≈ 39 cm³/m²	course’s arithmetic, taking one drop as 0.05 cm³
Brush — B&S Pt/Pd drop chart, 8 × 10	44 to 45 drops ≈ 2.2 cm³, ≈ 43 cm³/m²	as above
Brush — B&S Pt/Pd drop chart, 4 × 5	15 drops ≈ 0.75 cm³, ≈ 58 cm³/m²	as above
Brush — Ware’s reconstruction of Irving Penn’s practice	46 to 61 cm³/m²	Ware’s inference from Penn’s worksheets

The drop volume of 0.05 cm³ is Ware’s figure and every conversion in that table that uses it is the course’s own derivation, not a published number. The pattern it produces is nevertheless consistent across four independent sources: a rod uses about 30 cm³/m², a brush about 40 to 60. The two drop-chart rows also show the small-format penalty: on the same chart and the same conversion, a 4 × 5 print works out about a third dearer per unit area than an 8 × 10, because the sensitiser left on the brush and in the pot does not shrink with the paper.

🧮What the difference is worth

Take an 8 × 10 in sheet: 0.2032 m × 0.254 m = 0.0516 m².

• Rod at 30 cm³/m²: 1.55 cm³.
• Brush at 45 cm³/m²: 2.3 cm³.

That is 50 per cent more sensitiser per print, every print, for the life of your practice.

For a cyanotype it is pennies: Bergger state that their two 300 mL bottles coat about 300 sheets of 8 × 10, which is the whole argument for learning on this process. For platinum-palladium the same 50 per cent is applied to the most expensive solution in the course.

The course cannot turn that into a price. src/data/prices.json carries no dated UK listing for potassium tetrachloroplatinate or sodium tetrachloropalladate, so what is published here is the ratio and not the cost. The planner names its gaps; this is one of them.

The contamination rule

One brush per process, and never share. Bostick & Sullivan’s instruction is blunt and general: wash the brush thoroughly before using it again, because any solution left on it will be exposed and will contaminate your next print. A brush that has carried ferricyanide into a platinum sensitiser has not made a variant; it has made a defect that will appear in the wet processing and be impossible to diagnose from the print alone. A rod is rinsed under the tap immediately after each coating, before anything can crystallise on it, and a rod is much easier to keep genuinely clean than a bristle brush — which is a second, quieter argument for it.

Blot the residual liquid at the bottom of the coating with clean blotting paper. Ware’s reason is precise: crystals formed there can damage the negative.

The light, and why a dose is not a time

Part XVI owns this and this page cites rather than repeats it. Four things from it matter for choosing a negative and a paper.

The band. UVA, 320 to 400 nm, with maximum output near 365 nm, which Ware calculates to be the optimum wavelength for the siderotype processes. A lamp peaking near 410 nm is nearly wasted on a cyanotype, because hexacyanoferrate absorbs there and acts as an internal filter. Short-wave mercury lamps offer no advantage and much additional risk.

The dose, and the uniformity. Dose is irradiance times time, and both halves have to be established on your own equipment. The UVA exposure unit is commissioned by a uniformity map made on coated strips — nine strips cut from one sheet and exposed together, so that position is the only thing that differs between them — and then by a dose series. Its stated uniformity target is a quarter of a printing-out step across the printing area, expressed that way rather than as a percentage of irradiance because it is established by strip test and not by a meter, and a home unit has no instrument of known spectral response with which to justify a meter reading. Its geometry rule is pitch against height, with the array overhanging the printing area by at least the array-to-paper height on every side.

The one number that page publishes for irradiance — 25 W/m² at the paper — is a design target carrying an assumed 60 per cent coupling factor, and the page says so in terms: the calculation is an order-of-magnitude check, not a prediction of your exposure time, and the course publishes no claim it has not measured, and it has measured nothing on your box. Your dose series is the measurement, and until you have run it you do not have an irradiance, only an intention.

The geometry, which decides your sharpness. Any gap between negative and paper — from a bellied sheet, a carbon dioxide bubble, or a protective interleaf — is blurred by an amount that depends on the size of the source divided by its distance. Ware calls that ratio the aspect value:

blur = gap × (w ÷ d)

Blur from source geometry

w is the largest linear dimension of the source and d its distance from the print, so w ÷ d is the aspect value; gap is the separation between negative and sensitised surface. Take 0.3 mm of blur as the onset of a visibly soft image.

Source	Aspect value	Blur at a 0.1 mm gap	Blur at a 0.5 mm gap
The sun	0.01	0.001 mm	0.005 mm
NuArc 2125	0.1	0.01 mm	0.05 mm
A light bed, or open sky	4	0.4 mm	2.0 mm

That table settles several arguments at once. A bank of tubes close to the paper is a light bed, and under it a half-millimetre bubble is a 2 mm blur — catastrophic. Under the sun the same bubble is invisible. It is why the felt blanket and the porous paper matter more with a home-built array than with sunlight, and why a protective polyester interleaf over a precious negative must be no thicker than 20 µm under a close diffuse source, where 50 to 100 µm is tolerable under a small distant one.

Why one day’s minutes are not another’s. Mercury-vapour sources — which is all of them except LEDs and the sun — do not reach full output from cold; Ware warms his for five minutes and notes the tubes take about three to steady. Small high-intensity arcs drift enough that professional units carry a light integrator, an instrument that accumulates irradiance × time and reads out in dose rather than in minutes, precisely because the minutes are not comparable. And the sun varies with latitude, season, hour and cloud: Bergger hedge their own figure carefully, giving “approximately 10 minutes” for maximum density under a cloudless sky in Paris at noon in summer, which is a number with four conditions attached and is honest for it.

The sun is also nearly a point source, subtending half a degree, which gives it the finest acutance of anything on the list — and it moves through that same half degree in two minutes, so a long exposure is a slowly rotating source. The north summer sky is a light bed by comparison and about three stops weaker than direct sun.

The standard negative

One negative, chosen now, printed in every process you can reach, measured every time. It is the spine of Parts XXI to XXV and the thing that will eventually let the printing processes matrix say something it currently cannot: that page states plainly that its rows come from different photographers, papers and decades, so it describes what the processes are like and not what they do to one picture.

What makes a good subject. It has to survive being printed six or seven ways, which rules out anything that depends on one process’s particular gift.

• A full tonal range, with real information at both ends. A subject that is all mid-tones tells you nothing about the ends of the scale, and the ends are where these processes differ most.
• Highlight detail that is worth preserving. Printing-out processes are self-masking — density built in the shadows acts as a mask over the thinnest parts of the negative, delaying maximum density and letting the highlights print in — and that behaviour is invisible on a subject with nothing delicate in the high values.
• Texture rather than colour. You are comparing a blue print with a brown one with a grey one.
• A size that is the print size. These are contact processes at 1:1. If you are shooting film, that means large format or a small print; if you are making a digital negative, it means deciding the print size before you output.

Which density range? Make the standard negative for the long scale — 2.0 to 2.4 in the UVA covers New Cyanotype, print-out palladium and the platinum-palladium mixtures — and accept that the classic cyanotype needs a second, shorter negative or a different sensitiser. Ware makes exactly this point about composite printing: the New Cyanotype has about the same exposure scale as the platino-palladiotype so one negative serves both, whereas the classical process cannot render a negative made for platinum-palladium at all. Do not compromise the long negative to make the classic one work; you would lose the comparison that the whole exercise exists for.

📓What must be recorded about the standard negative, once

Written down once, at the top of the sheet that every process page in Parts XXI to XXV adds a row to.

Origin. Film stock and batch, developer, dilution, time, temperature and agitation; or the digital source file, the printer, ink set, driver settings, maximum-ink-density value and film substrate, with the date the negative was output and cured.

Contrast. The contrast index or gamma-slider value aimed at, and how it was arrived at.

Density range. The figure, the instrument, the spectral condition and the geometry, and whether it is visual, ultraviolet or a step count from a printed tablet. A number without those four is not usable by the next process.

Printing conditions. The source, its distance, the Standard Printing Exposure if you calibrated one, and the relative humidity.

Then, per print: the process, the sensitiser and its formulary page, the paper and batch, the coating method and volume, the dose, the measured maximum density and exposure scale, and the image colour in words. The lab notebook and the exposure log carry the fields; the curve plotting sheet takes the step-tablet readings.

Alternative route

This page declares that it needs an ultraviolet source, and it needs one for exactly two things: the optical-brightener comparison, and the calibration loop, which is a printing exercise and cannot be done without printing.

Sunlight is the honest alternative for the printing, and for cyanotype it is a good one. Ware’s arithmetic gives average sunlight 30 to 40 W/m² of UVA and full density in two to four minutes, and every supplier’s instructions in this cluster name the sun first. The sun is also, by the aspect-value table above, the sharpest source available to you at any price — a fact worth knowing before you envy somebody’s exposure unit. What you lose is repeatability, and the substitute is a written record: date, time, sky, orientation, elapsed time and the print’s appearance at each inspection through a split-back frame. Use the daylight exposure record and the outdoor exposure session procedures, which exist for this.

The calibration loop survives the substitution, with one change. The Standard Printing Exposure is defined in whatever unit your source is controlled by, and under the sun that unit is not minutes. Do the whole loop — the overexposed test print, the step count, the SPE, the ink-density adjustment — in a single session under an unchanging sky, so that every strip in the comparison had the same irradiance even though you cannot say what it was. Then record the conditions instead of the dose, and say so when you quote the result. A measurement whose limits are stated is a measurement.

The optical-brightener comparison has no substitute and does not need one. It was already offered here as a comparative observation rather than a test, because the course could not source a method for it. If you have no ultraviolet lamp, skip it and rely on the coated-strip test, which needs no lamp at all: coat, leave in the dark, and look at the colour. That is the test that actually decides whether the paper is usable, and it is available to everyone.

Everything else on this page needs no facility whatever. The exposure-scale arithmetic, the choice of paper, the alkali calculation, Lugol’s solution, the coating-volume comparison and the design of the standard negative are reading, arithmetic and paper-buying from end to end. A reader with no ultraviolet source can complete every decision this page asks for and arrive at the coating and printing lab with the right paper and the right negative in hand.

The ultraviolet hazard has no alternative route either. A reader printing outdoors has an unenclosed source of 30 to 40 W/m² that cannot be interlocked. Distance, sleeves, a hat and not looking at the source are administrative controls, the weakest kind, and knowing that is what Part XVI’s lesson is for.

Recap

The negative. In contact printing there is no Callier effect, so the negative’s ultraviolet density range and the process’s exposure scale are the same number. A grade 2 enlarging paper spans 0.90 of that axis; the classic cyanotype spans about the same, and everything else in this cluster spans 1.5 to 2.7. The published figures disagree, sometimes by a factor of two, and the disagreement is usually two different processes sharing a name — a chlorate-truncated development platinotype is not the print-out platinotype whose curves Ware measured. Reilly declines to publish a number for salted paper and albumen at all, and gives a grey-scale procedure instead, which is the more honest answer.

The measurement. A density is a number plus a spectral condition plus a geometry. Your Part XV densitometer reads green and has no ultraviolet channel; a pyro stain and an inkjet negative both read very differently at 365 nm, and the course publishes no conversion because none is sourced. Calibrate by printing: a step tablet, a Standard Printing Exposure of E × P ÷ 100, and the count of steps between the last maximum black and the first paper white.

The paper. ISO 9706 requires an alkaline reserve of 0.4 mol/kg, which on a 250 g/m² sheet is an eightfold molar excess of alkali over the iron you coat onto it. That alkali hydrolyses the sensitiser before exposure and destroys the Prussian blue after it — irreversibly, in one to ten minutes, at the pH of saturated chalk. The same reserve is required of a photo-safe enclosure for a silver gelatin print, because there the enemy is acid. One image substance, opposite prescriptions. Then: no clay, no retention aids, no brighteners, no titanium dioxide, no surface size, no aldehydes, unmixed cotton or linen furnish, hot-pressed, porous enough to let the carbon dioxide out, and 160 g/m² to A4.

The light. UVA around 365 nm, wasted at 410 on a cyanotype; dose rather than time, because lamps warm up and drift and the sun moves; and an aspect value that turns a half-millimetre gap into a 2 mm blur under a close bank of tubes and into nothing at all under the sun.

Three things this page could not establish, and says so rather than filling in: current UK availability and current specifications for the papers named — the list is dated 2020 and must be re-checked before buying; a published, validated hexacyanoferrate spot test for iron contamination in paper, so none is given as a method; and any published method or acceptance criterion for detecting optical brighteners in a sheet with an ultraviolet lamp, which is offered here only as a comparison against a known reference.

Check your understanding

Question 1. A negative measures a density range of 0.95 on your green-channel densitometer and prints beautifully at filter 2. You contact-print it on a New Cyanotype coating whose exposure scale is 2.2. What does the print look like?

• Harsh and contrasty, with blocked shadows and blown highlights
• Correct, because the process adjusts to whatever negative it is given
• Flat and dark at once: a small tonal excursion sitting low on the scale, with the paper white never reached
• Correct in the shadows and blank in the highlights

Show the answer and why

Answer: Flat and dark at once: a small tonal excursion sitting low on the scale, with the paper white never reached

The negative controls only 0.95 of the 2.2 log units the process can span, so the picture is compressed into the bottom fraction of the scale. The shadows go to maximum blue because even the thinnest part of the negative passes plenty of light, and the densest highlight is nowhere near enough to hold back the paper — so the print sits low and short. It is the opposite of contrasty: a short density range on a long-scale process always gives less contrast, not more. The first option describes the reverse mismatch, a long negative on the classic cyanotype.

Question 2. Photographers’ Formulary put the negative density range for their platinum kit at 1.0 to 1.5. Ware measures 1.5 to 1.8 for platinum. Which statement is the course’s position?

• Ware is right and the kit maker is wrong, because a book outranks an instruction sheet
• The average, about 1.4, is the safe working figure
• Both are right for their own process: the kit is a chlorate-truncated development platinotype and Ware’s figures are for a print-out sensitiser with no contrast agent
• The difference is measurement error and can be ignored

Show the answer and why

Answer: Both are right for their own process: the kit is a chlorate-truncated development platinotype and Ware’s figures are for a print-out sensitiser with no contrast agent

Potassium chlorate reoxidises part of the iron(II) photoproduct, making it unavailable to reduce the platinum, which shortens the exposure scale on purpose; Ware says the drop-counting chlorate system became standard practice precisely among users whose negatives were too short. So the kit describes a process deliberately adjusted to accept a shorter negative. Averaging two figures that belong to different processes gives a number that suits neither, which is why the course prints both with their conditions rather than one with none. Note that the reasoning here is the course’s interpretation, not a statement either source makes.

Question 3. A 300 g/m² paper conforms to ISO 9706. You coat it at 25 cm³/m² with a sensitiser 0.5 mol/L in iron(III). What is the molar ratio of alkaline reserve to iron(III), per unit area?

• About 4 to 1
• About 8 to 1
• About 10 to 1
• About 1 to 1

Show the answer and why

Answer: About 10 to 1

ISO 9706 requires at least 0.4 mol of alkali per kilogram, so 0.300 kg/m² × 0.4 = 0.12 mol of hydroxide equivalent per square metre. The coating deposits 0.025 L × 0.5 mol/L = 0.0125 mol of iron(III) per square metre. The ratio is 0.12 ÷ 0.0125 = 9.6, or about 10 to 1. Ware’s published figure of 8 is for a 250 g/m² sheet, and the point of asking for a heavier one is that the excess scales with paper weight: the more substantial the sheet, the more alkali it carries against the same coating.

Question 4. You calibrate an inkjet negative, find the SPE, and everything works. Six months later you replace the printer’s ink cartridges with a third-party set of the same nominal colours. What must you redo?

• Nothing, since the driver settings and film are unchanged
• Only the gamma slider value
• The whole calibration, from the 100-step tablet onwards
• Only the SPE, since the process has not changed

Show the answer and why

Answer: The whole calibration, from the 100-step tablet onwards

Ware lists four things the ink’s optical density range depends on — printer model, ink set, driver settings and film substrate — and says that if any of them changes it is necessary to recalibrate. The ink set is one of the four, and there is a reason it is not a small change: what you are matching is the ink’s density at UVA wavelengths, and two inks that look identical in visible light can differ substantially at 365 nm. That is the same trap as reading a negative visually, arriving from a different direction.

Question 5. Your platinum-palladium prints on one particular paper show woolly, cloudy lighter patches that correspond to fibre flocculation seen when the sheet is held up to the light. What does the evidence support?

• This is the blotching Ware attributes, as a hypothesis, to cationic retention aids trapping the sensitiser’s anions
• It is proven that this paper contains cationic polyacrylamide
• A decalcification soak in dilute hydrochloric or sulfamic acid might help, because small anions may neutralise the retention aids
• The classic cyanotype sensitiser would be expected to suffer the same defect on this paper

Show the answer and why

Answer: This is the blotching Ware attributes, as a hypothesis, to cationic retention aids trapping the sensitiser’s anions, A decalcification soak in dilute hydrochloric or sulfamic acid might help, because small anions may neutralise the retention aids

The description matches Ware’s account exactly, and he states the retention-aid mechanism as a hypothesis he cannot test, because papermakers do not disclose their additives — so nothing here is proof of what is in the sheet. The acid soak is his own suggestion, offered as a possible hidden benefit of decalcification and worth trying on that basis. The fourth option inverts his prediction: the traditional citrate and oxalate sensitisers are oligomeric and carry little ionic charge, which is his explanation for why classic cyanotype and development platinotype do not generally blotch, so the same paper may well behave perfectly in cyanotype.

Question 6. Two workers coat the same 8 × 10 in sheets with the same platinum-palladium sensitiser; one uses a rod, one a brush. Roughly what is the difference in solution consumed per print, and why does the same difference not matter much in cyanotype?

• About 10 per cent, and cyanotype chemistry is bought in larger bottles
• About 50 per cent — roughly 1.55 cm³ against 2.3 cm³ — and cyanotype sensitiser is cheap enough that a set of two 300 mL bottles coats about 300 such sheets
• About four times, and cyanotype is coated on cheaper paper
• There is no reliable difference; it depends entirely on the paper

Show the answer and why

Answer: About 50 per cent — roughly 1.55 cm³ against 2.3 cm³ — and cyanotype sensitiser is cheap enough that a set of two 300 mL bottles coats about 300 such sheets

A rod runs at about 30 cm³/m² and a brush at roughly 40 to 60, and an 8 × 10 sheet is 0.0516 m², so the two figures are about 1.55 and 2.3 cm³. Paper absorptivity does matter — Ware says so explicitly — but it does not erase a consistent 50 per cent gap seen across four independent sources. The reason it is tolerable in cyanotype is arithmetic, not sentiment: Bergger state that two 300 mL bottles coat about 300 sheets, so the extra volume costs almost nothing, while the same proportion applied to a noble-metal salt is the difference between prints you can afford and prints you cannot.

Question 7. You print with a bank of UV tubes 8 cm above the frame, and your prints are slightly soft in areas of high local contrast although the negative is sharp. Which explanations are consistent with the geometry taught here?

• A close bank of tubes has an aspect value near 4, so even a 0.1 mm gap gives 0.4 mm of blur — past the 0.3 mm threshold for a visibly soft image
• Carbon dioxide from the photochemical reaction may be forming a bubble layer because the paper is backed with an impervious sheet rather than felt
• The tubes emit at 410 nm, which blurs the image
• A thick protective polyester interleaf over the negative would make it worse under this source

Show the answer and why

Answer: A close bank of tubes has an aspect value near 4, so even a 0.1 mm gap gives 0.4 mm of blur — past the 0.3 mm threshold for a visibly soft image, Carbon dioxide from the photochemical reaction may be forming a bubble layer because the paper is backed with an impervious sheet rather than felt, A thick protective polyester interleaf over the negative would make it worse under this source

Blur is gap times aspect value, and a light bed at close range has the largest aspect value of any source in the table — which is why the same fault would be invisible under the sun. Both listed causes of the gap are real: the evolved carbon dioxide needs a porous path out through the verso into a felt blanket, and an interleaf under a close diffuse source must be no thicker than 20 µm where 50 to 100 µm is tolerable under a small distant one. Wavelength is the wrong axis entirely: 410 nm costs a cyanotype speed, because ferricyanide absorbs there and filters the light internally, but it does not soften an edge.

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