Break/Fix: The Cyanotype That Went Wrong

Six sheets are drying on the line and not one of them is right. That is a normal Saturday in this part of the course, and it is also the most efficient teaching situation the whole cluster offers, because six different faults on one afternoon’s work are six independent measurements of the same bench.

The temptation is to change everything at once — a new paper, a fresh bottle, distilled water, a shorter wash — and print again. It would probably work. It would tell you nothing about which of your habits was wrong, and next month you would be here again with a different paper and the same fault. Every change you make before you collect evidence destroys evidence, and in this process the evidence is unusually cheap to collect and unusually easy to throw away, because most of it lives in the two centimetres of paper around the edge of the picture.

The situation

You have run the coating and printing lab twice and the exposure-scale experiment once, so you know what your sensitiser, your paper and your light source do when they are behaving. Today they are not.

It is a Saturday in July. You are printing on a new box of a heavyweight cotton paper that the shop recommended, from a bottle of classic sensitiser mixed three weeks ago, under a bathroom window with the blind down, with a fluorescent tube on overhead because the afternoon has clouded over. The wash is the kitchen tap into a tray in the sink, and it is a hard-water district. Two of the six prints were coated with a rod and four with the hake brush you also use for kallitype. You did not mask the negative, so the coated area and the exposed area are the same rectangle.

The six results:

1. No white anywhere. A pale blue veil over the whole sheet, highlights included.
2. Yellow highlights, faintly, on a print that otherwise looks acceptable — and a print from a fortnight ago, mounted, that has gone visibly darker in its whites since.
3. A print that faded in the wash, in front of you, over about ten minutes, leaving a yellow-brown ghost where the deepest blue had been.
4. A flat, weak print whose darkest tone is a mid-blue and whose wash water ran distinctly blue.
5. A blotchy sheet with hard-edged pale patches and, on one of the rod-coated ones, evenly spaced streaks in the direction of the stroke.
6. A print whose shadows are paler than its mid-tones, with a metallic sheen on the sheet you pulled from the frame before washing.

Those are six symptoms and possibly fewer than six faults. Two of them are not faults at all. One of them is not even a printing problem: it is the tap.

Before you start

Level B, and the level is set by the bench rather than by any single substance. Cyanotype chemistry is not the hazardous part of this cluster — the sensitisers are odourless, no fumes are normally evolved, and Ware states plainly that no special ventilation is needed in the workplace. What raises this above Level A is that a diagnostic session has you handling several solutions at once, some of them deliberately faulty, some of them decanted into unlabelled vessels because you were in a hurry, and that potassium ferricyanide is incompatible with concentrated acids. Gloves and eye protection for the whole session, one labelled vessel per solution, and nothing goes back into a stock bottle.

The ultraviolet is the real hazard and it does not soften because you are diagnosing. Whether the source is a lamp or the sky, the Part XVI unit page governs, and the UV unit SOP is the one to have open. Repeat exposures for a differential mean more time beside the source than an ordinary printing afternoon does.

Three things about a diagnostic session in particular.

You will be making deliberately bad prints. That is the point, and it means the tray sequence runs longer and the trays sit fuller than usual. Wash water carrying Prussian blue and dissolved iron salts goes to the general chemical waste route if your authority requires it, and local regulation governs; the course cannot tell you what your council accepts.

Do not add acid to anything without checking what is already in the tray. The one genuine chemical trap in this part is a strong acid meeting ferricyanide, and a diagnostic bench with four trays and three bottles is exactly where that happens by accident.

Sweat and hand oils mark this material. Jacquard’s own instruction sheet names them as a cause of discoloration, and warns against wetting the paper before or during exposure and against damp hands. On a day when you are handling twelve sheets instead of two, that stops being a nicety.

Alternative route

Without an ultraviolet unit, the whole page works, and sunlight is the honest substitute. Every supplier’s own sheet lists the sun first, and the part overview argues the case in full. What you lose is not the diagnosis but the control: a differential that compares two sheets must expose them under a sky that has not changed between them, so pair your tests, expose them side by side in one frame where you can, and record sky, time and orientation on the daylight exposure record rather than pretending to a dose.

Without a densitometer, everything here still works. Every discriminator on this page is a pattern — where the tone is, whether the margin matches the picture, whether the fault was there wet or arrived on drying, whether a second sheet from a different box behaves differently. Patterns are read by laying two sheets side by side in even daylight. What you lose is the ability to say how much, which matters for the record and not for the diagnosis.

Without a second paper you cannot run the paper differential, which is the single most productive test on the page. Any genuinely different sheet will serve — a scrap of a different make, a page torn from a sketchbook, an offcut from a friend — provided you write down what it was. What you must not do is skip the control and reason as though you had run it.

Without distilled water you cannot run the water differential either, and here the substitute is poor. A supermarket bottle of still mineral water is not distilled water and carries the dissolved calcium the test is trying to remove. Deionised water sold for steam irons and for car batteries is the cheap source, and the Part III measuring-pH lab is where the reading technique comes from.

Without any wet space at all there is no route to making the prints, and this page says so plainly rather than pretending otherwise. What survives is the reading: the symptom vocabulary, the three reference regions, the algorithm and the case-by-case reasoning are all followable from a photograph of somebody else’s failed print, and a reader in that position should work through them before the afternoon they matter rather than during it.

The symptoms

Describe what you see before you name it. Four pairs of words do most of the work in this process, and each pair separates two faults with different cures. Do this with the prints dry and fully oxidised — which for a cyanotype means several hours after the wash, not ten minutes — in even daylight, beside a print you were happy with.

Say this	Not this	Because
The tone is grey-blue	The tone is yellow	Ware’s distinction and the most useful single sentence in the diagnosis. Fog is unwanted image substance and reads grey to blue; stain is unwanted residual chemistry, chiefly iron(III) salts, and reads yellow. Different causes, different cures, and they can both be present
The shadows are pale and the mid-tones are dense	The whole print is pale	Reversal attacks the most heavily exposed areas and leaves the mid-tones alone. Peptisation takes the whole scale down and empties the highlights. The shadows point in opposite directions
The image faded during the wash	The image was never dense	A print that visibly loses density in front of you is being taken apart — by alkali or by peptisation. A print that came out of the frame weak was never made
The sheen is on the unwashed print	The sheen is on the finished, dried print	A bronze surface before the wash is the normal appearance of a fully exposed sheet, on Jacquard’s own instructions. Anything metallic on a finished print is something this course cannot source

The three regions every sheet should carry

Almost everything below depends on being able to compare parts of one sheet with each other, and that is a decision you make before you coat, not after the print fails. Ware’s own procedure requires two reference areas and his printing-frame section requires a third.

One sheet, three reference regions and a blocking patch

1. 1Uncoated margin — bare paper, never sensitised. Any tone here is contamination in a bath or a tray, not a coating fault
2. 2Coated but masked border — sensitised, then covered during exposure. Any tone here happened without light: sensitiser, paper or wet chemistry
3. 3Blocking patch beside the negative — a scrap of film opaque to ultraviolet. If it stays clean and the negative shadow does not, the negative is the fault
4. 4Picture area — the only region in which exposure is a candidate explanation at all

Ware makes the point sharply in his printing-frame section: mask the negative with a window of ultraviolet-opaque film, and the coated-but-masked border becomes a tell-tale check on whether the clearing worked. Expose the whole coated sheet instead and you will never know for certain whether the print is properly cleared and the highlights undegraded. The masking has two further benefits he names — less carbon dioxide evolved during the exposure, which degrades resolution, and far less redundant non-image pigment made in the wet processing, which can bleed into and stain the picture.

Today’s six prints were made without a mask. That is not a moral failing; it is why three of the six diagnoses below will need a re-print before they can be settled, and it is the first habit to change.

Evidence to collect

Cheapest first, and the cheapest tests here are astonishingly cheap. Two of them cost nothing but a strip of indicator paper, and between them they explain a large fraction of all cyanotype failures. Collect in this order and stop when the answer is unambiguous.

The order to collect evidence in, cheapest and least destructive first

1. 1Read the sheet you already haveDry, oxidised, in daylight. Grey-blue or yellow? Where is the tone — margin, border, picture? Costs nothing and rules out whole branches.
2. 2Test the wash waterpH by indicator paper or meter, plus your supplier hardness figure. Two minutes. Ware forbids anything above pH 7 and any hard supply.
3. 3Test the paperA drop of dilute acid on a corner of an uncoated offcut. Fizzing is a carbonate buffer, and a buffered paper is disqualifying.
4. 4Look at the sensitiserIs the mixed solution still clear yellow-green? Is there a blue tinge, a blue deposit, a mould? Costs a glance at the bottle.
5. 5Coat a test sheet with all three regionsUncoated margin, masked border, blocking patch. This is the sheet the algorithm is designed to read, and everything after it depends on having one.
6. 6Run one differential at a timeWater, paper, sensitiser, coating tool. One variable per pair of half-sheets, both halves from the same coating.
7. 7Only then change the exposureExposure is the variable everyone reaches for first and the one that explains fewest of these faults.

The sequence is not arbitrary: the first four steps cost minutes and no materials, and on this course's reading of the sources they account for most of what goes wrong.

The water test, in detail, because it is the one most readers skip. Fill a glass from the tap you wash in and read its pH — indicator paper is enough to separate 6.5 from 8, and the Part III lab covers the meter if you have one. Then find your supplier’s published hardness figure for your postcode, in milligrams per litre as calcium carbonate. Thames Water, as one example of the published bands, calls anything up to 100 soft, 100 to 150 slightly hard, 150 to 200 moderately hard, 200 to 300 hard and above 300 very hard, and states that the whole of its region is hard because the water passes through chalk.

Where the threshold sits, and how much of it is sourced. Ware’s own instruction is a boundary rather than a number: alkaline water above pH 7 must not be used, nor hard water containing calcium salts, which will damage the Prussian blue image. Jacquard’s is shorter still — use distilled water if your tap water is hard. Photographers’ Formulary specify a five-minute wash in soft water and warn about hard and alkaline supplies. The measured consequence is in Ware’s Table 9.6 and in the earlier work he cites: the Moor experiments of 1989 recorded an average image-density loss of 18 per cent in tap water at pH 7.5 to 8.5, 4 per cent in distilled water at pH 6 to 6.5 and 0.00 per cent in deionised water at pH 6.3 to 6.6, all at fifteen minutes.

!The course's own rule, and the part of it that is not sourced

Sourced: above pH 7, or any supply the utility classifies as hard, the wash is damaging the image, and the size of the damage runs from a few per cent to nearly a third of the density depending on water and washing time.

The course’s own derivation, stated as such: a practical threshold of pH 7.0 and 150 mg/L as calcium carbonate — the top of the “slightly hard” band — above which this course recommends distilled or deionised water for the final rinse, and acidification of the first bath within the limits the formulation tolerates. Neither figure is published as a threshold by any source in this course’s corpus. They are the point at which the sourced boundary (pH 7) and the sourced classification (hard) coincide, and they are offered as a working rule rather than as a measurement. If your supply is over the line, the honest test is the differential below, not this number.

Hints, in increasing order of disruption

Work down only as far as you need to. Each hint costs more than the one above it.

1. Look at the edge of the sheet before you look at the picture. Three of the six cases are decided by a region most printers throw away.
2. Wait. A cyanotype is not finished when it is dry. The reversed shadows darken and the colour intensifies over several hours as the air re-oxidises Prussian white, and a print judged at ten minutes has been judged against the wrong object.
3. Ask when the tone first appeared — on coating, during drying, after exposure, after wet processing, after the wash. That single question is the whole of Ware’s algorithm.
4. Test the water and the paper before you touch the chemistry. Both tests are cheap and both are more often the answer.
5. Split a sheet. Coat one sheet, cut it in two after exposure, and process the halves differently. One variable, one coating, one exposure: the only comparison worth making.
6. Coat a sheet and expose it to nothing at all. A sheet that fogs in the dark has settled the question of whether light is involved.
7. Change the paper. The most productive single substitution in this cluster, and the one most readers try last.

The diagnosis

Ware’s algorithm for fogged highlights, and how to work it

Fogged highlights have at least six causes, they look identical on the finished print, and guessing between them is a lottery. Mike Ware published a systematic separation of them — as Table 7.1 of Cyanomicon §7.6, and as a standalone one-page workshop handout — and this course teaches his algorithm rather than an invented one. The six causes, in his numbering:

1. The sensitiser is already decomposed.
2. There is a hostile chemical in the paper, reducing the sensitiser.
3. The safelighting is inadequate under the conditions of working.
4. The mask or negative is not dense enough in its maximum value.
5. The wet chemistry is faulty, chemically reducing the sensitiser.
6. The clearing procedure is inadequate, leaving residual iron.

The structural idea is that the causes act at different stages, so the stage at which the tone first appears identifies the cause. That is why the algorithm is a sequence of questions about when and not about what, and why it needs the two reference regions: you are asking whether a border that was coated but never exposed is darker than a margin that was never coated at all.

Ask, in this order	If yes
Fog apparent on coating?	Sensitiser decomposed (1), or a very hostile chemical in the paper (2)
Fog appears during drying? Then: does it still fog if dried in total darkness?	Yes — hostile paper chemical (2). No — faulty safelight (3)
Fog appears after a print-out exposure?	Mask or negative not dense enough in its maximum value (4)
Fog after wet processing?	Sensitiser decomposed (1), faulty safelight (3), thin mask or negative (4), or faulty wet chemistry (5)
Stain of sensitiser after the wash?	The clearing procedure is inadequate (6)
Stain in uncoated areas of the paper?	The wet chemistry is contaminated (5)

Three notes travel with the table and each is load-bearing. Distinguish fog from stain by colour: fog is unwanted residual image substance and is grey, stain is unwanted other residual chemicals, especially ferric salts, and is yellow. Cause four is detected with a blocking patch: include a small area of high ultraviolet blocking — Ware names Rubylith — beside the negative and compare it with the negative’s own maximum density; if the patch stays clean and the negative’s densest shadow does not, the negative is the fault and the chemistry is innocent. And some branches depend on whether the process prints out or develops: fogging from a faulty safelight may not be visible until wet processing is complete, which is why the fourth row lists four causes rather than one.

=How to run the algorithm when your failed print has no border

Today’s six prints were exposed without a mask, so the second column of the table has nothing to read. You cannot run the algorithm backwards on a finished print; you run it forwards on the next one.

Coat one sheet with a margin left bare and a border that will be masked. Cut it into four before drying. Dry one quarter in room light, one in total darkness, expose the third under the negative with a blocking patch beside it, and process the fourth without exposing it at all. Four quarters, one coating, four stages — and between them they answer every row of the table in a single afternoon.

Case one: blue fog in the highlights, and no clean white anywhere

Run the algorithm first. On the evidence of one unmasked sheet you have four candidates in play, and the differential below separates them.

Sensitiser age is the candidate to check first because it costs a glance. The classic mixed sensitiser has, in Ware’s words, an inconveniently brief shelf-life; Jacquard put a number on it and say the mixed sensitiser is stable just two to four hours. The separated stocks are the durable part: Bostick & Sullivan give about a year in the original separate containers, and Jacquard call the stocks stable long term. A three-week-old mixed bottle is not a formula, it is a suspension of Prussian blue that has been making itself in the dark, and it will fog every highlight it touches. Look at the bottle: a blue tinge or a blue deposit is the diagnosis, and neither filtering nor dilution restores what has been consumed.

Paper contamination is the second candidate and the most likely on a new box. Anything in the sheet that will reduce iron(III) makes Prussian blue without any light at all. Ware’s test is the coated sheet itself: the coated side should remain light yellow, and a drift towards green or blue in the dark condemns the paper. He notes that the New Cyanotype sensitiser is a particularly sensitive test of paper quality for exactly this reason, especially if the coated sheet is left some hours in the dark at normal humidity. His remedy where the paper is otherwise wanted is citric acid in the sensitiser to about 2 per cent, one drop of 0.05 cc of a 40 per cent w/v solution per cc — added to the working mixture and never to the stock, because it shortens the shelf-life.

Humidity is the third and it is the one that explains a bad afternoon rather than a bad box. The citrate sensitiser is deliquescent; a coated sheet that stays tacky marks the negative, prints softly, and does not dry to the condition the exposure was calibrated for. Ware’s own working humidity is about 55 per cent relative, with at least an hour for a coated sheet to dry in the dark. He also records that rapid drying can reduce chemical fogging from paper impurity — and, in the same breath, that over-rapid drying may worsen the loss of image substance in the wash. There is no free move here.

Stray light is the fourth and today it has a name: the fluorescent tube. Ware’s processing-environment section is explicit that no darkroom is needed, that ordinary curtains or blinds make a sufficient dim room, that a 40 W tungsten bulb at two metres or more is safe for the periods normally needed — and that fluorescent light should be avoided where possible, because some tubes have a significant ultraviolet output that may fog sensitised paper. Switching that tube off is free.

And there is a fifth cause that belongs to the tray rather than the paper. Ware records that any inclusion of ferric ions in the developer for a cyanotype leads to blue fogging of the background, because iron(III) in the presence of hexacyanoferrate(III) is a powerfully oxidising pair whose reduction product is insoluble. A first bath that has done ten prints is carrying iron. So is a tray that had sensitiser spilled in it last week. Ware’s simple-cyanotype sheet limits a litre of 1 per cent citric acid to two or three prints; his New Cyanotype notes give the acid bath a capacity of six to ten 10 × 8 prints per litre and say not to re-use it. Neither figure is a suggestion.

One more trap on the acid, and it is specific to which formula you are printing. The classic and simple sensitisers tolerate only a very weak acid — under 1 per cent citric — and Ware states that if the bath is too strong it will cause blue fogging of the highlights and degrade the paper white. A mineral acid at 1 per cent belongs to the New Cyanotype and will fog a classic print. If you have recently printed both, this is where the two processes collide.

The differential. Coat four quarters from one sheet as described above. Then: fresh sensitiser on old paper, old sensitiser on fresh paper, both dried in total darkness, and one quarter developed in plain water rather than acid. The quarter that comes out clean names the fault. The blue-fog atlas entry carries the full cause list and the hexametaphosphate rescue for a sheet already fogged.

Case two: yellow highlights that darken over weeks

This is stain, not fog, and the colour is the whole diagnosis. Yellow is residual iron(III) sensitiser that the wash never carried out. It matters more than it looks, because the print you mounted a fortnight ago has gone on changing in the frame.

Why it darkens later. Two mechanisms are in the sources and they are not exclusive. Residual iron(III) salt in the sheet is still light-sensitive; and residual iron(III) hydrolyses in the paper to a hydrated iron oxide that is yellow-brown, insoluble and inclined to bind to cellulose. Ware’s own observation is that a low pH assists clearing precisely because it prevents that hydrolysis — which means a neutral or alkaline wash can manufacture the stain it was supposed to remove. Jacquard’s sheet names the same outcome from the other end: yellowing may occur where prints are exposed to phosphates or high pH solutions.

Ware’s published end-point test, and it is the one to use. The criterion for completed processing is the total removal of the yellow stain of sensitiser from unexposed areas, and the test is optical: hold the print up to a bluish light, or view it through a blue optical filter, and check that no yellow remains in the interior of the paper. If any persists, wash further. A blue filter works because the pigment absorbs in the red and the stain absorbs in the blue, so under blue light the image goes light and the stain goes dark — the opposite of how they look in daylight, which is why the fault is so easy to miss.

✕The chemical spot test the manifest asked for, and what the course could and could not find

What is published and what is not. This course searched its corpus for a chemical spot test for residual iron in a washed cyanotype — a reagent, a sensitivity and a false-positive list — and did not find one. Ware’s monograph, which is the fullest technical account of the process in print, gives the optical test above and no chemical one. The Getty atlas describes the water bath as both completing the blue and dissolving the unexposed sensitiser and offers no test of completion. No manufacturer’s sheet in the corpus specifies one.

What the corpus does establish is the chemistry a test would rest on. Ware records, in his appendix on Prussian brown, that the mixture of iron(III) and hexacyanoferrate(III) rapidly turns blue when spotted onto cellulose filter paper or any other oxidisable substrate, because the pair is powerfully oxidising — a redox potential of about +1.5 V, driven by the insolubility of the product — and that this has been the basis of a qualitative analytical spot test in the inorganic-analysis literature.

So the course offers this, labelled as its own derivation and not as a published method. On a sacrificial offcut of the washed sheet, a drop of dilute potassium ferricyanide solution on the highlight area will turn blue if iron is still present, because the cellulose reduces the iron(III) and the resulting iron(II) precipitates Prussian blue with the ferricyanide. Its limits are real and should be stated with it: no sensitivity is published, so it tells you whether and never how much; it destroys the area it is applied to, so it is not a test on a finished print; it responds to iron from any source, including a rusty clip or a contaminated tray, so it does not distinguish inadequate clearing from contamination; and because the reaction needs an oxidisable substrate, it may behave differently on a heavily sized sheet and is not applicable to cloth of unknown fibre. The three-region reading is the better test in every case where you have one, and this is a fallback for a sheet that does not.

The three-region reading settles the cause even when it cannot measure it. Yellow in the coated-but-masked border and not in the uncoated margin is inadequate clearing, cause six. Yellow in the uncoated margin as well is contaminated wet chemistry, cause five, and no amount of extra washing will fix a contaminated tray. The yellow-stain atlas entry carries the stain-removal literature and the reason this course does not hand it over as a procedure.

Case three: the print that bleached in the wash

Watch it happen and you have most of the diagnosis. A cyanotype that loses density in the wash in front of you, over minutes, and leaves a yellow-brown residue where the deepest blue was, has been hydrolysed by alkali. The residue is the tell: it is hydrated iron(III) oxide, the same substance as the stain in case two arrived at from the opposite direction, and it is what is left when the pigment is taken apart.

Fe[Fe(CN)₆]⁻ + 3 OH⁻ → Fe(OH)₃ + [Fe(CN)₆]⁴⁻

Alkaline hydrolysis: half the image stays in the paper as iron(III), and half leaves as hexacyanoferrate(II)

The numbers are what make this urgent rather than theoretical. Ware reports Holtzman’s finding that a buffer at pH 9.4 completely decolourises Prussian blue by irreversible hydrolysis in one to ten minutes — and then puts that number where it hurts: pH 9.4 is the pH of a saturated solution of calcium carbonate, the buffer routinely built into archival papers and boards. Sodium carbonate at 0.25 molar, about pH 10.7, does it in less than half a minute.

Two suspects, and two cheap tests that separate them.

The paper test. ISO 9706 permanent paper is specified to have 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. Ware works out what that means for a coated sheet: a 250 g/m² permanent paper carries an eight-fold molar excess of alkaline reserve over the iron(III) that a normal coating deposits on it. So the sheet is not neutral ground; it is a reagent. The test is a drop of dilute acid on a corner of an uncoated offcut — visible effervescence is carbonate, and a carbonate-buffered paper is disqualifying for this process without pre-treatment.

The water test, exactly as set out under Evidence. And then the differential that settles it beyond argument: coat one sheet, expose it, cut it in two, wash one half in tap water and the other in distilled or deionised water for the same time. If the tap half is markedly weaker, the water is the fault; if both are equally weak, look at the paper.

Distinguish this from light fading, which it resembles. Light fading of a cyanotype is substantially reversible: a faded print regains in the dark over days. Alkaline hydrolysis does not regain at all, and it leaves iron behind. The alkaline-bleaching atlas entry carries the partial-restoration literature and its limits.

Case four: a weak, flat print, and blue in the wash water

Look at the wash tray. If it ran blue, the diagnosis is peptisation and it took no equipment. Prussian blue in this process is formed as very fine particles, and what looks like dissolution is a peptised colloid: particles fine enough to disperse and travel and pass a filter. If they were never securely lodged inside the surface cellulose fibres, the wash carries them away, and what you are left with is empty highlights and a truncated scale — Ware lists it as the fifth of the classic process’s seven shortcomings and says the only remedy traditionally offered is gross over-exposure, which damages quality and makes exposure impossible to judge.

The candidate causes, ranked by how often the sources make them the answer.

1. The water. First because it is measured, cheap and usually wrong. Ware’s own washing table compares five historic sensitisers in tap water at pH 7.2 against purified water at pH 6.5, and the four-hour losses run to between 0.14 and 0.31 in density units in tap water against 0.02 to 0.03 in purified water for most of them. Solutions of high ionic strength promote peptisation, which is why hardness matters as much as pH.
2. Absorption — the paper and the wetting agent. These processes depend on the sensitiser getting into the interfibrillar space within the fibres. Ware names poor absorption as the third of the classic process’s shortcomings, and the remedy as a surfactant; a heavily sized sheet that holds the solution in the surface pores gives an image that leaves in the wash.
3. The wash itself. The end point is the disappearance of yellow, not the clock. Ware’s classic instruction is a face-down wash until the yellow sensitiser has entirely gone from the highlights, about twenty minutes; Jacquard’s is at least five minutes with the water changed until it runs clear. Beyond the end point you are only removing image.
4. The negative. The classic process has an exposure scale of only about 0.9 — three stops, comparable with a grade 3 silver paper. A long-range negative made for platinum cannot print on it, and the result reads as flat. This is a fit problem, not a fault, and the negatives and papers lesson is where it is solved.
5. Coating volume and sensitiser strength. Last, because it is the one most readers adjust first. The formulary pages carry the quantities; this page will not restate them.

The confirming test is the split sheet in two waters, exactly as in case three. It separates “the image washed out” from “the image was never made”, and those have nothing in common. The weak-density atlas entry carries the rest.

Case five: blotchy or streaked coating, and what the pattern tells you

The geometry of the fault names the cause, so look at the shape before the cure.

Pattern	Cause	What to change
Streaks along the stroke, evenly spaced	The tool: too little solution on the rod, or a stroke that ran dry	More solution, more passes, and a rod held at a constant angle without pressure
Hard-edged pale patches that look like drops that never spread	Wetting: the sensitiser sat on the surface instead of entering the fibres	A surfactant, or a less heavily sized paper
Small sharp white spots, scattered	Crystals — a gritty sensitiser	Filter the solution; check for a potassium-bearing contaminant
Directionless mottle over broad areas	The paper’s sizing, the humidity, or a fingerprint	A different sheet, 55 per cent relative humidity, and dry hands
Brush marks worse in one corner	Over-brushing: the sensitiser worked after it began to dry	Coat quickly and stop; the working time is short

Two of those rows have a chemical cause worth naming. Ware’s account of the crystal row is potassium iron(III) oxalate coming out of an oxalate sensitiser — a sparingly soluble salt in a concentrated solution — and he raises the possibility that brush marks and other defects may themselves be due to friction promoting the formation of microcrystals in the coating. That is a route from a contaminated bottle to a fault that looks purely mechanical, and it is why the crystal row and the streak row are not as independent as they appear.

And the humidity row is the deliquescence again. Above about 55 per cent relative humidity the citrate coating stays tacky, and a tacky sheet neither dries evenly nor contacts the negative properly. The blotchy-coating atlas entry has the full list, and the coating lab has the technique.

Case six: reversal in the shadows, and the bronze that is not a fault

Two appearances, and only one of them is wrong.

The bronze is expected. Jacquard state it as the normal condition of a fully exposed sheet — the fabric will look bronze in colour once fully exposed, and with wetting, the print will change from a bronze to blue colour — and a printer who cuts the exposure to avoid it will under-expose every print they make. Ware’s description of a correctly exposed classic sheet is the same object seen from the other side: the highlights distinctly green, the shadows somewhat reversed, and the whole image looking rather blocked up.

The reversal is real, it is over-exposure, and it is documented. As the exposure continues, the most heavily exposed areas go paler rather than darker, ending as a pale blue-grey. Herschel named it solarisation in 1842 and Ware gives the mechanism in his appendix on the photochemistry of the blueprint process, together with the reasoning that selects between the competing explanations.

The mechanism, because the manifest asked whether one is published and one is. Ware sets out two proposals. Suzuki’s, in which prolonged exposure photoreduces the hexacyanoferrate(III) directly to hexacyanoferrate(II), which then makes colourless Prussian white with the iron(II) photoproduct, is judged inadequate on two grounds: the quantum yield for hexacyanoferrate(III) photoreduction is too low for it to contribute significantly, and adding a small proportion of white pigment does not account for the extensive reversal actually seen, in which blue already formed is observed to be reduced. Murray’s proposal is the one Ware supports: the heavy exposure makes an excess of the iron(II) complex, and that reduces the Prussian blue already present to Prussian white.

[Fe(C₂O₄)₂]²⁻ + Fe[Fe(CN)₆]⁻ → [Fe(C₂O₄)₂]⁻ + Fe[Fe(CN)₆]²⁻

Murray's mechanism for solarisation: the iron(II) photoproduct reduces the blue already formed to colourless Prussian white

The redox potentials support it — Ware gives about +0.02 V for the iron(III)/iron(II) oxalate couple against about +0.46 V for the Prussian blue/Prussian white couple — and he confirmed it experimentally by irradiating a solution of ammonium trisoxalatoferrate(III) and immersing a processed step test in it: the strip bleached, a control in the same solution unirradiated did not, and the bleached strip re-oxidised in air, proving the change had been a reduction and not hydrolysis or peptisation. A further experiment then showed the bleaching is much faster and more complete when the print is irradiated in situ, from which he infers that Prussian blue itself becomes photochemically activated, in an excited charge-transfer state, and is easier to reduce in that state. So the mechanism is not one step but two contributions, and Ware says so.

⁇Bronzing: what this course could source, and what it could not

The manifest asks whether bronzing in cyanotype has a published explanation. On this course’s corpus, it does not have one as a defect of a finished print. Cyanomicon does not use the word at all, and no manufacturer’s sheet in the corpus describes a metallic sheen on a washed, dried cyanotype.

Two things adjacent to it are published and are not the same phenomenon. Jacquard describe bronze as the normal, expected appearance of a fully exposed unwashed sheet, which is a stage rather than a fault. And Ware, writing about the commercial blueprint papers of the reprographic era, names a different degradation with a different name: because the light-sensitive iron salt is necessarily in great excess over the ferricyanide in a fast copying paper, even slight over-exposure generates excess iron(II) which washes into unexposed areas as bleeding, and in the exposed areas adversely affects the quality of the colour, giving it a greyish cast, called “burning out”. That is a documented over-exposure defect of the shadows — but it is grey, not metallic, and Ware attributes it to excess iron(II) and not to a surface effect.

So the course describes a metallic sheen on a finished print as an observation and asserts no mechanism for it, and treats a bronze sheen before the wash as the expected condition. If your metallic appearance survives the wash and full oxidation, record it, photograph nothing you cannot source, and treat it as an open question. The atlas entry reaches the same conclusion independently.

The confirming test for reversal is to wait. Prussian white is colourless and it comes back: several hours in air, or half a minute in 0.3 per cent hydrogen peroxide, which Ware states makes no difference to the final densities. If the pale shadows fill in, nothing was wrong. If they stay pale after full oxidation, the exposure genuinely went past the point of return for that paper and that sensitiser, and the fix is less exposure. Under no circumstances use a dichromate bath to re-oxidise, whatever the older literature says; Ware’s prohibition is unambiguous and the ammonium dichromate page says why.

Cross-contamination, which becomes the commonest fault the moment there are two processes

Everything above assumes one chemistry on the bench. The moment a second alternative process joins it, the dominant fault changes, because in this cluster the contaminants are each other’s reagents.

Potassium into an oxalate sensitiser. Ware calls mixing New Cyanotype sensitiser with Simple or Classic a chemical nonsense: the whole laborious point of the New preparation is to remove potassium ions, and putting them back allows crystals of sparingly soluble potassium iron(III) oxalate to form on the paper and wreck the print. A shared pipette is enough.

The wrong developer on the right print. New Cyanotype wants a mineral acid — 1 per cent nitric or hydrochloric, or 5 per cent sulfamic. Classic and Simple tolerate under 1 per cent citric and fog blue in anything stronger. Two processes in one evening, four trays, and this is the error that happens.

Hexacyanoferrate(II) meeting an unexposed sensitiser. A ferrocyanide-bearing bath — from a toner, from a bleach, from a neighbouring process — makes Prussian blue with iron(III) directly, with no light at all. That is Pellet’s positive process working where it is not wanted.

Fe³⁺ + [Fe(CN)₆]⁴⁻ → Fe[Fe(CN)₆]⁻

The unwanted route: hexacyanoferrate(II) contamination makes the same pigment from unexposed sensitiser

Oxalate destroying a finished blue. A platinum developer will bleach and dissolve Prussian blue, so a cyanotype printed under a platinum print is destroyed by that print’s own processing. Ware’s order rule is specific: platinum first, cyanotype second, never the reverse.

And a finished image acting on a fresh sensitiser without light. Ware reports that coating a processed platinum–palladium print with New Cyanotype sensitiser has been observed to deposit Prussian blue immediately on the graduated tones without any exposure, and suggests the metal image may be acting catalytically. Neither party is a contaminant; they are two finished chemistries meeting.

The test is a blank. Coat a sheet with each sensitiser using the tools you actually use, process each by its own route, and expose none of them. Blue on a sheet whose formula contains no ferricyanide means a tool or a tray is carrying it. And the last row of Ware’s algorithm is the same test in miniature: stain in the uncoated margin means the wet chemistry is contaminated, not the coating. The cross-contamination atlas entry carries the full route list.

The fix

In the order the evidence licenses, and not before.

Case one, blue fog. Mix sensitiser in the volume you will use in the next two hours and not more. Switch off the fluorescent tube and work under tungsten at two metres. If the coated sheet drifts green in the dark, change the paper; if the paper is otherwise wanted, add citric acid to about 2 per cent in the working mixture only. Replace the first bath on the schedule the source gives rather than when it looks tired — two or three prints per litre for 1 per cent citric on the simple sensitiser, six to ten per litre for the New Cyanotype’s acid bath, no re-use. A sheet that is already fogged can be rescued in 5 to 10 per cent sodium hexametaphosphate, which strips blue from the highlights — at a cost to the whole image, since it works by promoting the peptisation that case four is about.

Case two, yellow stain. Wash longer, in more water, changed rather than static, and judge the end point by blue light rather than by the clock. Acidify the first bath within the limits the formulation tolerates. If the yellow will not lift after a further twenty minutes in fresh water, the iron has hydrolysed and no amount of water will move it; re-print, and mask the negative this time so the border tells you before the picture does.

Case three, alkaline bleaching. Distilled or deionised water for the final rinse, immediately. Change the paper, or pre-treat it — Ware’s decalcification is 5 per cent v/v hydrochloric acid or 5 to 10 per cent w/v sulfamic acid for about ten minutes, then wash — and note that he calls it tedious and a last resort rather than a routine. Get the print off any alkaline mount or enclosure; this is the one photograph in the course whose storage requirement is the opposite of standard archival practice.

Case four, weak and flat. Water first, surfactant second, wash end point third, negative fourth. If the negative is genuinely short for the process, no processing change will rescue it, and the honest fix is a different negative or a different formulation with a longer scale.

Case five, blotchy coating. Filter the sensitiser. Add the surfactant. Coat quickly with enough solution and stop working the surface. Equilibrate the paper to about 55 per cent relative humidity and give a coated sheet the hour it wants in the dark.

Case six, reversal. Wait, or oxidise, before judging. Then expose less if it is genuinely reversed — and remember that the manufacturers’ advice runs the other way for ordinary work, because over-exposure is where this process is forgiving.

⚗One correction that applies to every peroxide bath you will ever run

Both re-oxidations of Prussian white — by air and by peroxide — consume protons and generate hydroxide ions. Ware notes that these may build up sufficiently to cause some hydrolysis of the Prussian blue, and that the oxidations should therefore for preference be carried out under acidic conditions.

That is a small change with a real consequence: a peroxide bath made up in a hard, mildly alkaline tap supply is running the alkaline-hydrolysis reaction of case three at the same time as the re-oxidation it was meant to perform. Make it up in the same water you wash in only if that water is below pH 7; otherwise make it up in distilled water. Bostick & Sullivan’s own bath is 100 mL of 3 per cent hydrogen peroxide in 900 mL of water, and Ware’s is 0.3 per cent for no more than half a minute.

The rule of this cluster

Most cyanotype faults are in the paper or the water, not in the chemistry, and the diagnostic sequence should start with the cheapest test. That is the general lesson of this page and it is worth stating as a rule because it runs against instinct: the bottle is the thing you made, so it is the thing you suspect, and it is the least likely culprit of the four.

Consider what the sources actually blame. Ware’s seven shortcomings of the classic process include a sensitiser poorly absorbed by paper fibres, peptisation caused by poor retention by the paper, and an exposure scale that fails to match the negative — three of seven that are properties of the substrate or the fit, not of the formula. His conservation chapter blames the paper’s alkaline reserve for the destruction of the image, and quantifies an eight-fold molar excess of alkali over iron in a standards-compliant sheet. His washing table makes the tap a first-class variable in the maximum density. Jacquard’s instruction sheet, which has room for about twenty lines of advice, spends them on distilled water, mould, storage, phosphates, pH, sweat and dry hands — every one of them a condition rather than a recipe.

The corollary is an ordering, and it is the flow diagram under Evidence. Read the sheet you have. Test the water. Test the paper. Look at the bottle. Coat a sheet with the three regions. Run one differential. Change the exposure last. The first four steps cost minutes and no materials; the last is the one most printers try first, and it explains fewer of these faults than any of the others.

A second corollary, about the shape of the evidence. This is a printing-out process, so the image is visible before any processing, which means the stage at which a fault appears is nearly always observable. That is a luxury the silver processes do not have, and Ware’s algorithm is built entirely on it. Use it: a fault you can date is a fault you can name.

What to record

A failed print is only worth its afternoon if the next one is an experiment rather than a repetition. Use the lab notebook and add these, which are what this page’s reasoning actually consumed.

About the materials.

• The paper: make, weight, batch if printed, and whether it is buffered — with the result of the acid-drop test, not the marketing on the packet.
• The sensitiser: which formula, which formulary page, the date the stocks were made and the date and time the working mixture was made. These are different numbers and the second is the one that expires.
• The iron salt’s supplier and batch. The citrate varies in iron content between suppliers and between lots, and a change here changes your exposure.

About the conditions.

• Relative humidity and temperature at coating, and the drying method — air or heat, and how long. Heat-drying and air-drying are not interchangeable once you have calibrated: Ware measures heat-drying as shortening the exposure scale by about a stop.
• The working light: what kind, what wattage, how far away.
• The wash water: pH, the supplier’s hardness figure, whether the final rinse was distilled, and how many prints the first bath had already done.
• The interval between exposure and processing. Ware measured 19 hours of “darktime” as lengthening the exposure scale from 2.3 to 2.6 while weakening the maximum density and causing edge fog, and concluded it is best avoided — but only a recorded interval lets you know whether it was a variable.

About the print.

• Which of the three regions carried the fault, and at which stage it first appeared. This is the single most useful line in the record and it takes six words.
• The appearance when pulled from the frame, before the wash, and again at the wash’s end, and again the following morning after full oxidation. Three observations of one print, because it is three different objects.
• What you changed, one item, and what it did.

Where this page stops

Toning faults belong to the toning lab, not here. A print that changed colour in a tannin bath is a different subject, and the toner’s own formulary page carries its fault list.

Faults on cloth are partly out of scope. The scale and fabric assignment treats wash-fastness as an open question and this page does not settle it. The diagnostic reasoning transfers; the spot test explicitly does not, because it needs an oxidisable cellulose substrate.

Anything that requires an instrument this course has not built — a pH measurement on a dry paper surface, an ultraviolet density reading of a negative, a hardness titration — is named as a limit here rather than approximated. The densitometer part and the Part III pH lab are where two of the three become available.

And where the sources are silent, this page says so rather than filling the gap: there is no published chemical spot test for residual iron in a cyanotype in this course’s corpus, no published sensitivity for the one the course derives, no published explanation of a metallic bronzing defect on a finished print, and no published numeric threshold for water hardness — only a boundary at pH 7 and a classification of “hard”. Four gaps, each of them a place a reader with a better source could improve this page.

Questions

Check your understanding

Question 1. A cyanotype comes out of the wash with a uniform pale blue veil across the highlights. You have one sheet, exposed without a mask. Which single decision made before the coating would have narrowed the six candidate causes to two, and why?

• Coating a heavier layer of sensitiser, because a thicker coating fogs less
• Leaving an uncoated margin and masking a border during exposure, because the algorithm identifies the cause from the stage at which the tone first appears, and both reference regions are needed to see a stage that happened without light
• Using a longer exposure, because fog is a symptom of under-exposure
• Filtering the sensitiser, because fog is caused by particles

Show the answer and why

Answer: Leaving an uncoated margin and masking a border during exposure, because the algorithm identifies the cause from the stage at which the tone first appears, and both reference regions are needed to see a stage that happened without light

The algorithm is a sequence of questions about when the tone appeared, not about what it looks like, and every one of those questions is answered by comparing a coated-but-unexposed border with an uncoated margin. Without the border you cannot tell whether the tone arose before any light reached the sheet; without the margin you cannot tell whether a bath is contaminated. A heavier coating makes fog worse if the paper is the cause. Exposure is irrelevant to a fault visible in unexposed areas. Filtering addresses crystals, which give sharp white spots rather than a veil.

Question 2. Two prints from the same coating and exposure are washed for the same time, one in tap water at pH 8 and one in deionised water. The tap-water print is visibly weaker. Which mechanism does that result support, and which does it rule out?

• It supports under-exposure and rules out the paper
• It supports loss of image substance in the wash — peptisation promoted by ionic strength, with alkaline hydrolysis as a second contribution at that pH — and it rules out any cause acting before the wash, because both halves shared one coating and one exposure
• It supports fogging and rules out the negative
• It supports a decomposed sensitiser and rules out the water

Show the answer and why

Answer: It supports loss of image substance in the wash — peptisation promoted by ionic strength, with alkaline hydrolysis as a second contribution at that pH — and it rules out any cause acting before the wash, because both halves shared one coating and one exposure

The design of the test is what gives it its power: everything before the wash is held identical by using one coating and one exposure, so any difference between the halves has to have arisen in the tray. That excludes sensitiser age, paper fogging, safelight and negative density at a stroke. What it cannot do is separate the two water-borne mechanisms from each other, because at pH 8 both peptisation and alkaline hydrolysis are running; distinguishing those needs the yellow-brown residue, which hydrolysis leaves and peptisation does not.

Question 3. You pull a sheet from the printing frame and its shadows are paler than its mid-tones. What should you do before concluding anything, and what would each outcome mean?

• Re-expose it immediately; if it darkens the exposure was short
• Wash it and judge at once; the wet print is the finished print
• Complete the processing, then wait several hours in air or give a brief 0.3 per cent hydrogen peroxide bath, and look again: if the pale shadows fill in, that was Prussian white on its way back to blue and nothing was wrong; if they stay pale after full oxidation, the exposure genuinely reversed past the point of return
• Add a dichromate bath, which is the traditional re-oxidiser

Show the answer and why

Answer: Complete the processing, then wait several hours in air or give a brief 0.3 per cent hydrogen peroxide bath, and look again: if the pale shadows fill in, that was Prussian white on its way back to blue and nothing was wrong; if they stay pale after full oxidation, the exposure genuinely reversed past the point of return

Reversal is a real over-exposure phenomenon, but most prints reported as reversed are prints judged too early: Prussian white is colourless and re-oxidises to Prussian blue over several hours in air, or in about half a minute in dilute peroxide, and Ware records that the peroxide route makes no difference to the final densities. Re-exposing a processed print tests nothing. The wet print is not the dry print. And the dichromate bath is specifically prohibited: Ware's instruction is that under no circumstances should it be used for this, although it was once commonly recommended, and he points to the medical literature describing in some detail the unpleasant consequences to an artist who used a dichromate bath for quilting fabrics.

Question 4. A student prints New Cyanotype and Classic Cyanotype on the same bench in one evening, using one brush and one set of pipettes. Which fault should be expected first, and what is the chemistry behind it?

• Weak maximum density, because the two sensitisers dilute each other
• White crystalline specks in the coating, because potassium carried into the oxalate sensitiser precipitates sparingly soluble potassium iron(III) oxalate on the paper — the very thing the New Cyanotype preparation exists to remove
• Yellow stain, because the two washes have different end points
• Reversal, because the two processes have different exposure scales

Show the answer and why

Answer: White crystalline specks in the coating, because potassium carried into the oxalate sensitiser precipitates sparingly soluble potassium iron(III) oxalate on the paper — the very thing the New Cyanotype preparation exists to remove

The New Cyanotype preparation is an elaborate crystallisation whose entire purpose is to eliminate potassium ions, so reintroducing them from a shared pipette or an unwashed brush undoes the preparation directly and deposits a sparingly soluble salt where the image should be. Ware also suggests the same microcrystal formation may be behind brush marks, which is why an apparently mechanical coating fault can have a contamination cause. The other three are real faults with other causes: dilution would lower density but not produce specks, the wash end point is the same criterion for both, and the exposure-scale difference is a negative-matching problem rather than a contamination one.

Question 5. Which of these does this page decline to give a number for, and why does the refusal matter to a diagnosis?

• The capacity of the acid development bath, because no source publishes one
• The sensitivity of a chemical spot test for residual iron, and a numeric water-hardness threshold — neither is published in this course's corpus, so each is named as a gap rather than filled with a plausible figure, and a diagnosis resting on an invented number would be resting on nothing
• The pH at which Prussian blue hydrolyses, because it varies with the paper
• The exposure scale of the classic process, because it depends on the light source

Show the answer and why

Answer: The sensitivity of a chemical spot test for residual iron, and a numeric water-hardness threshold — neither is published in this course's corpus, so each is named as a gap rather than filled with a plausible figure, and a diagnosis resting on an invented number would be resting on nothing

Three of the four name figures this course does have. Ware gives the acid bath two or three prints per litre for 1 per cent citric and six to ten per litre for the New Cyanotype bath. Holtzman's pH 9.4 destroying Prussian blue in one to ten minutes is a measured figure, and Ware gives it. The classic exposure scale of about 0.9 is published and is a property of the process rather than of the lamp. The genuine gaps are the spot test's sensitivity and a hardness threshold, and the reason the distinction matters is procedural: a stated gap sends you to a differential test, while an invented number sends you to a conclusion.

Check my answersClear

Recap

Six failed prints, and the reasoning that separates them fits on one page because the process makes its faults visible early. Fog is grey and stain is yellow, and that one sentence splits half the case list. The stage at which a tone first appears identifies its cause, which is Ware’s algorithm and the reason a coated-but-masked border and an uncoated margin belong on every sheet you make. Reversal attacks the shadows and peptisation attacks the whole scale, so the shadows are the discriminator between over-exposure and image loss. A print that fades in front of you in the wash is being hydrolysed, and the yellow-brown residue is the proof.

Beneath all six sits the rule this cluster teaches and the silver processes do not: the paper and the water are chemistry, not context. A standards-compliant archival sheet carries an eight-fold molar excess of alkali over the iron you coat onto it, and a hard tap supply can cost a third of the image density in four hours. Test them before you touch the bottle. And where a number would help and no source gives one — the sensitivity of a spot test, a hardness threshold, a mechanism for a metallic sheen on a finished print — this page names the gap and sends you to a differential, because a diagnosis built on an invented figure is not a diagnosis at all.