Assignment: The Process Comparison Atlas

The brief

Print one negative in every process you can reach, measure all of them the same way, and fill one row of the process comparison atlas from each print you made rather than from anything you read.

That is the whole assignment, and it is worth saying at the front that nobody in the published literature appears to have done it. The course’s own printing processes matrix says so in its scope: what is published there is assembled from different photographers, different papers and different decades, which tells you what the processes are like and not what they do to the same picture. Its own words are that the comparison the design ultimately asks for — one negative printed in seven processes in one darkroom — “is owned by the Part XXV assignment, nobody has printed it, and no column here is a substitute for it.”

You are not doing an exercise. You are making the measurement the course has been unable to cite.

What you hand in is three things: a set of prints from one image that can be laid side by side, a completed atlas row for each process with every field filled and every claim classified, and a written argument saying which process you would use for which picture, defended in terms of the fields you measured rather than in terms of taste.

The processes

Seven, and they are the seven the matrix already carries as subjects, so your rows go straight into it.

#	Process	Where you learned it	Image substance
1	Silver gelatin, fibre base	Part XIX	Developed silver in gelatin on baryta
2	Cyanotype	Part XXI	Prussian blue among the fibres
3	Salted paper	Part XXII	Printed-out silver, gold-toned
4	Albumen	Part XXIII	Printed-out silver in an albumen layer
5	Van Dyke Brown	Part XXIV	Iron-reduced silver among the fibres
6	Kallitype	Part XXIV	Iron-reduced, developed silver
7	Palladium	This part	Palladium metal among the fibres

Platinum is not on the list and will not be. The course’s ruling of 4 September 2026 is that students perform palladium and never handle platinum, and the matrix’s own scope says so in the same words. Where you want a platinum comparison, it comes from the published curves and the conservation descriptions, marked as read rather than measured — and the chemistry lesson carries the figures.

An eighth row is available and is worth taking if you can: the palladium-toned kallitype, which is the accessibility route this part recommends and which nobody has compared against a palladium print in the literature the course has read.

Learning objectives

By the end of this assignment you will be able to:

• Make one comparison rather than seven descriptions, by holding the subject, the negative, the measurement method and the observer constant.
• State a process’s exposure scale as a number and use it to say what negative that process wants.
• Record a surface and an image colour reproducibly, with the method and its limits written down.
• Express relative speed as a ratio across processes that use different sources.
• Write a mechanism for each process in your own words, in three or four sentences, and be right.
• Classify every claim you make as measured, published or inferred, and know why that matters more than the claim.
• Cost a print from your own records, dated, with the assumptions stated and the gaps named.
• Report your own failure rate honestly, which is the field most atlases omit and the one a beginner most needs.

Prerequisites

Every practical page of the cluster, because this assignment prints all of them:

• Experiment: tonal scale, contrast and image colour in palladium, which establishes the measurement method you will use on all seven.
• Clearing, toning and the permanence of iron-silver prints.
• Sensitising, printing and toning albumen paper.
• Printing, toning, fixing and washing a salt print.
• Cyanotype exposure scale and contrast, which is where you first measured an exposure scale and where the standard negative was chosen.
• Print critique and the exhibition print, for the vocabulary of the written argument, and for the silver gelatin row.

Safety classification

Level B, taking the highest classification of the processes it requires, and the new risk is not a new chemical.

Cross-contamination is the dominant hazard of this assignment, and it is a fault as well as a hazard — its own troubleshooting entry records what it looks like in a print. It puts silver nitrate, oxalates, noble-metal salts, hexacyanoferrate solutions and ultraviolet exposure into the same week and often onto the same bench. Every one of those hazards is one you have already met and controlled in isolation; what you have not done before is run them adjacently.

Four rules govern, and none of them is new — what is new is that they now have to hold at once.

• The acid rule for hexacyanoferrates is absolute. No acid, no acidic bath, no acidified rinse and no acidic waste goes near the cyanotype chemistry or its waste bottle. Every other process in this list has an acid step somewhere. Part XXI established the rule and this assignment is where it is hardest to keep.
• Oxalate and silver must never meet, on the incompatibility recorded on oxalic acid’s page: silver oxalate is explosive when dry. That means separate glassware, separate trays and separate tongs for the palladium bench and the silver benches, not shared and washed.
• Sulfide and selenium chemistry stays off this bench entirely. If you are toning anything in Part XX’s baths, do it in another session in another place.
• Dedicated brushes, rods, trays and tongs per process, and clearly labelled waste containers for silver-bearing, iron-bearing and noble-metal-bearing solutions. Three bottles, three labels, set out before anything is coated.

Students who take the accessibility route and omit the palladium row remove the noble-metal sensitisation hazard and none of the others. Silver nitrate is still corrosive, the hexacyanoferrate rule still holds, and the ultraviolet source is still a source.

Every hazard control from Parts XXI to XXV applies, and none is relaxed because the session is a comparison rather than a first attempt. Each process’s own page carries its own controls, and this page does not restate them.

What is not a new hazard here, and why. Printing seven processes does not create a chemistry that none of them has: there is no combination step, no bath is shared, and nothing is mixed across processes. The risk is entirely in adjacency and in fatigue over a long session, and the controls for both are procedural — separate benches or separate days, everything labelled, and a written running order so that the acid step and the ferricyanide step are never the same afternoon.

Materials

Material	Quantity	Note
The standard negative	1, and see the matched-set discussion below	Chosen in Part XXI
Papers appropriate to each process	3 or 4 sheets each	Unbuffered cotton for the hand-coated six; fibre-base enlarging paper for the silver gelatin row
Calibrated transmission step wedge	1	Printed alongside every process, on the same sheet where possible
Sensitisers, developers, toners and clearing baths for seven processes	per each process’s own page	Nothing new is introduced by this page
A dated physical colour reference	1 set	The control strips from each part, mounted and dated
Storage folders passing the Photographic Activity Test	enough for the set	The finished set is an object worth keeping

Estimated cost

Band £££, and it is the cheapest way to make an expensive comparison, because six of the seven processes cost pence per sheet and the seventh dominates.

The honest way to plan it is to count sheets rather than pounds. Allow three or four attempts per process — seven processes at four sheets is twenty-eight coated sheets — of which the palladium ones are the only ones with a serious material cost. Print the palladium row at 4 × 5 inches if the budget is tight; at about a quarter of the area it is about a quarter of the metal, and every measurement in this assignment works at that size.

Estimated consumables cost

This is the one page in the course where the consumables table is also part of the assignment, because field seven asks you to compute it from your own records. What follows is what the price file can and cannot support for the session as a whole.

Consumed	This assignment	Sourced price	Cost this session
Nitrile gloves	about 8 pairs across the sessions	£6.64 to £14.99 per box of 50 to 100	£1.06 to £2.40
Fibre-base enlarging paper, 8 × 10 in, for the silver gelatin row	4 sheets	£47.04 for 25 sheets to £150.28 for 100, glossy variable contrast	£6.01 to £7.53
Paper developer	about 500 mL of working solution	£10.52 to £20.03 per 500 mL to 1 L of concentrate at 1+9	about £0.50 to £1.00
Rapid fixer	about 500 mL of working solution	£21.05 to £25.98 per litre of concentrate	about £0.40 to £0.50
Sodium sulfite, anhydrous	25 g, for the palladium clearing bath	£13.68 to £19.98 per kg	£0.34 to £0.50
Silver nitrate	for the salt print, albumen, Van Dyke and kallitype rows	£59.95 for 25 g, or £112.90 for 10 g	Compute from your own records: this is field seven
Unbuffered cotton paper for six hand-coated processes	about 24 sheets	Not priced. Hot-pressed cotton paper is among the file’s named gaps	—
Ferric oxalate; sodium tetrachloropalladate(II) solution	about 3 mL each	Not priced. Both are gaps the price file names, on the account the coating lab gives	—
Ammonium iron(III) citrate; potassium ferricyanide; gold salt; tartaric acid; citrate salts; EDTA	per each process	Two of the six are priced, both at £17.99 per 230 g: the iron citrate and the ferricyanide. The gold salt, the tartaric acid, the citrate salts and the EDTA are not, and the matrix’s own empty cost cells say so for the kallitype, the Van Dyke and the palladium print	Compute the two priced ones from your own records, as for the silver

The priced subtotal is about £8.30 to £11.90, and it is a floor rather than a total by a very long way. Two of the nine rows carry no price at all and a third carries one for only two of its six salts, and between them they hold every hand-coated sensitiser in the assignment. The silver row and the two priced iron salts have prices and no totals, because computing those is field seven.

And that is itself a result you should report. The matrix’s cost column has three empty cells — the kallitype, the Van Dyke and the palladium print — each with a stated reason, and the palladium one says outright that “the most expensive process in the matrix is the one with no score, and that says something true about the course’s shopping data rather than about the process.” Your own dated receipts are better data than the course currently holds. Record them.

Alternative route

This assignment declares a darkroom, an ultraviolet source and mains equipment, and a reader may be missing any of them. Each has an honest answer and one of them changes what you hand in.

No darkroom. Only the silver gelatin row needs one. The other six are contact-printed in room light or under tungsten, exactly as their own pages set out. Print six rows and mark the seventh as the course’s published data, which is what the accessibility section below describes in full. You lose the reference row that every other row is compared against, so say in the analysis which process you used as your reference instead and why.

No ultraviolet unit. Sunlight, for all six hand-coated processes, and the requirement is the same one Part XXI sets: expose the whole comparison in one session under an unchanging sky, so that the relative speeds you report are valid against each other even though the absolute dose is unknown. Record date, time, orientation, cloud and elapsed time through the daylight exposure SOP and the outdoor exposure session SOP. Field four then reports ratios only and says so — which is what it mostly wants anyway.

No mains, or no densitometer. The density fields become step counts: for each process, the wedge step at which a tone first lifts from paper white and the step at which two adjacent steps stop separating. Report it as a step count with a stated precision of one step, and label the field as a step count rather than a density range. It is a coarser measurement and it is a real one.

One thing has no alternative. Every process here is wet, and there is no version of this assignment that produces prints without a sink and a wash. If that is the obstacle, the reading version of this page is worth doing anyway — read the seven atlas entries, read the matrix and its empty cells, and write the final argument from the published data with every sentence marked as published. What you cannot then claim is a measurement.

The standard negative, and the problem with it

One negative is the whole point. Every difference you record between two prints has to be attributable to the process, and the only way to get there is to hold everything else still: the subject, the negative, the paper where the process allows it, the light source, the observer, the instrument and the day.

What must be recorded about it, before you print anything: the film and developer, the measured density range in visual and — where you can measure it — in ultraviolet, whether it is an in-camera negative or a digital negative, and if digital, the correction curve applied and to which process it was calibrated. That last is not a detail. A digital negative with a correction curve baked in is not one negative; it is a family of negatives with a family resemblance.

!One negative cannot suit all seven, and this is where the assignment gets interesting

The exposure scales of these processes span a factor of three, and the numbers are published.

Process	Exposure scale	Source
Classic cyanotype	about 0.9 — three stops, comparable with a grade 3 enlarging paper	Ware, Cyanomicon
New Cyanotype	about 2.2, which Ware says matches negatives also intended for salted paper, platino-palladiotype, argyrotype or chrysotype	Ware, Cyanomicon
Simple cyanotype	about 2.7, with a maximum density of about 1.4	Ware, Cyanomicon
Traditional platinotype sensitiser, unmodified	about 2.0	Ware, Platinomicon
Print-out palladium	about 2.4, with a mid-tone slope of about 0.78	Ware, Platinomicon
Print-out platinum	about 1.9, with a slope of about 0.96	Ware, Platinomicon

A negative made for the classic cyanotype will print flat to invisible in palladium, and a negative made for palladium will print with blocked shadows and empty highlights on a classic cyanotype. That is not a subtlety; it is more than a stop and a half of difference in what the negative must carry.

So you have two honest options and the assignment requires you to state which you took and what it cost.

Option A — one compromise negative. Pick a density range in the middle of the spread, print everything from it, and report for each process how far its own scale is from what the negative supplied. The comparison of processes is clean because the negative really is identical. What you give up is that no print is the best that process could make, and the flattest and steepest processes are both penalised.

Option B — a matched set from one image. One capture, one file or one interneg, with a correction curve per process so that each negative’s density range matches that process’s exposure scale. Every print is the best that process can do. What you give up is that the negatives are no longer identical, so a difference between two prints may be a difference between two curves — and you must publish the curves you applied for anybody to check you.

The course does not tell you which to choose. It tells you that choosing silently is the one unacceptable option, and that the choice belongs in the first paragraph of your report.

The eight fields

One row per process, eight fields per row. Each field below says what is measured, how, and what the honest limit of the method is.

The eight fields, and what each one is for

1. 1One — tonal scale, measuredExposure scale and maximum density from a wedge, with the method and its precision stated, and all seven curves plotted on one pair of axes
2. 2Two — surfaceGloss, texture, and whether the image sits in the paper or on it, recorded in raking light at a stated geometry
3. 3Three — image colourBy the course's stated method, against a dated physical reference, never from memory
4. 4Four — sensitivity and exposureSource, dose and time for each, and relative speed expressed as a ratio
5. 5Five — chemistryA short mechanism statement in your own words. This is where the assignment tests understanding rather than technique
6. 6Six — permanenceWhat you are prepared to claim for each print and on what evidence, with every sentence classified as measured, published or inferred
7. 7Seven — costConsumables per print from your own records, dated, with the assumptions stated and the gaps named
8. 8Eight — difficultyFailure rate, session length and what went wrong. The field most atlases omit and the one a beginner most needs

Field one — tonal scale, measured rather than described

Print the step wedge in every process, on the same day, and read it 24 hours after drying on the Part XV densitometer in reflection mode. From each curve take:

• Exposure scale, ΔlogH. Use one definition for all seven and state it. Ware’s own definition for his tables is from fog plus 0.04 to 0.9 of maximum density, and it is a good one to borrow precisely because it is published.
• Maximum density.
• Mid-tone slope.

R = ΔlogH(process) ÷ ΔlogH(silver gelatin)

Relative exposure scale, against your reference process

Plot all seven on one pair of axes. That single figure is the most useful thing this assignment produces, and it is what the matrix cannot show.

What the plot will look like — three published scales, drawn to teach

• Classic cyanotype, ΔlogH about 0.9
• Silver gelatin enlarging paper, ΔlogH about 1.05
• Palladium, ΔlogH about 2.4

Show the numbers behind this plot

Three curves drawn on one pair of axes to show the spread this assignment measures. A classic cyanotype curve rises steeply and reaches its maximum within about 0.9 log units of exposure, so it is the leftmost and steepest. A palladium curve rises through a long gently curved toe at a much shallower slope and reaches a lower maximum density after about 2.4 log units, so it is the rightmost and flattest. A silver gelatin enlarging paper curve sits between them, reaching its maximum after about 1.05 log units at a steep slope and at the highest maximum density of the three. The point of the figure is the horizontal spread: the widest and narrowest scales differ by roughly a factor of three, which is why one negative cannot suit both ends. All three curves are drawn to published exposure scales and were not measured by the course.

Series	log relative exposure	Reflection density
Classic cyanotype, ΔlogH about 0.9	0.00	0.04
Classic cyanotype, ΔlogH about 0.9	0.20	0.18
Classic cyanotype, ΔlogH about 0.9	0.40	0.52
Classic cyanotype, ΔlogH about 0.9	0.60	0.95
Classic cyanotype, ΔlogH about 0.9	0.80	1.22
Classic cyanotype, ΔlogH about 0.9	0.90	1.30
Classic cyanotype, ΔlogH about 0.9	1.20	1.32
Classic cyanotype, ΔlogH about 0.9	2.70	1.32
Silver gelatin enlarging paper, ΔlogH about 1.05	0.00	0.04
Silver gelatin enlarging paper, ΔlogH about 1.05	0.20	0.12
Silver gelatin enlarging paper, ΔlogH about 1.05	0.40	0.38
Silver gelatin enlarging paper, ΔlogH about 1.05	0.60	0.80
Silver gelatin enlarging paper, ΔlogH about 1.05	0.80	1.34
Silver gelatin enlarging paper, ΔlogH about 1.05	1.05	1.85
Silver gelatin enlarging paper, ΔlogH about 1.05	1.40	1.98
Silver gelatin enlarging paper, ΔlogH about 1.05	2.70	2.00
Palladium, ΔlogH about 2.4	0.00	0.06
Palladium, ΔlogH about 2.4	0.30	0.09
Palladium, ΔlogH about 2.4	0.60	0.16
Palladium, ΔlogH about 2.4	0.90	0.29
Palladium, ΔlogH about 2.4	1.20	0.48
Palladium, ΔlogH about 2.4	1.50	0.72
Palladium, ΔlogH about 2.4	1.80	0.98
Palladium, ΔlogH about 2.4	2.10	1.24
Palladium, ΔlogH about 2.4	2.40	1.42
Palladium, ΔlogH about 2.4	2.70	1.45

Drawn to teach, not measured. The cyanotype and palladium exposure scales and the palladium maximum density are Ware's published figures; the silver gelatin curve is drawn to the shape Part XIII teaches at a representative scale, and your own Part XIII measurement replaces it. Your seven measured curves replace all three. The curve is drawn to show the shape, not measured from a real material. Your own materials will differ, and measuring them is what the sensitometry part of the course is for.

The honest limit. Your densitometer is a green-channel instrument, not a status-density one, and a reflection density is fully defined only by its geometric and spectral conditions. So your numbers are comparable with each other and are not directly comparable with a published figure measured on different apparatus. Say so once, in the method section, and then use them freely.

Field two — surface

Photograph or examine each print in raking light at a stated geometry, and state it: the light at a measured angle to the paper — 15 degrees is a common choice and any repeatable angle will do — the print flat, the observer normal to it, and the same light for all seven.

Record three things:

• Gloss, on a scale you declare and apply to all seven. Matte, semi-matte, glossy is enough if you define the words by naming which print is your example of each.
• Texture, which is the paper’s for six of the seven and the emulsion’s for one.
• Where the image sits. In the fibres, in a thin layer on the fibres, or in a coated layer over a baryta ground. This is the field the conservation literature is strongest on, so compare: the AIC describes the noble-metal image layer as embedded within the top fibre structure of the support, and the Graphics Atlas marks up a platinum print under the headings paper fibres visible, matte surface and layer structure, which is precisely the distinction you are recording.

The honest limit. Gloss meters exist and you do not have one. A declared scale applied consistently by one observer to seven prints under one light is a real comparison and not a measurement, and the difference matters when somebody else tries to use your row.

Field three — image colour

Use the method the course has already established rather than inventing one, so that your rows are comparable with the rest of the course’s data. It is set out in full in Part XX and adopted unchanged by this part’s experiment:

1. Compare, never recall. Every print laid against every other under one light.
2. Use the conservation literature’s vocabulary, naming the two terms a hue sits between rather than inventing a scale.
3. Take a number from your own instrument: a green-channel and a blue-channel density on one mid-tone patch, reported as a difference. It is a colour signal defined by your densitometer, not a colour measurement.
4. Keep a dated physical reference, mounted, in the dark, with the conditions on the back.

The honest limit is the whole of point three, and it must appear in your report: a two-channel density difference is reproducible on your instrument and meaningless on anybody else’s. A spectrophotometer would settle it in CIELAB coordinates; the course specifies none and the planner prices none.

Field four — sensitivity and exposure

Record for each process: the source (which lamp, or the sun with its conditions), the distance, the dose where you can compute one, and the time to a matched result.

Then express speed as a ratio, because the absolute numbers do not transfer:

S(process) = t(reference) ÷ t(process)

Relative speed

matched at the same maximum density on the same negative under the same source. Plot the seven on a logarithmic axis, because the range is large: Ware’s arithmetic from the Stark–Einstein law puts the maximum possible sensitivity of any proto-photographic material at about 34 J/m² for a just-perceptible image, which on a photographic scale is about 10⁻⁵ ISO — one ten-millionth of an ordinary film. Six of your seven processes live down there and one does not.

One published comparison to test yourself against: the Image Permanence Institute record that platinum was about three times faster than silver chloride printing-out papers and could be printed in diffused light. Your palladium against your salt print is the same comparison with two substitutions, and whether your ratio lands anywhere near three is worth a sentence.

The honest limit. A ratio measured under one source does not necessarily hold under another, because the processes have different spectral sensitivities and lamps have different spectra. Part XVI’s dose lesson has the argument; what you owe the row is the source, named.

Field five — chemistry

Three or four sentences per process, in your own words, saying what makes the image. No quotations, no formulary links standing in for an explanation. This is the field that tests whether you understood the cluster, and it is quick to mark because the errors are always the same ones.

The four distinctions the field is looking for:

• Does light make the image, or an invisible precursor that something amplifies? Only one of your seven amplifies. Part XXI’s overview makes the point in orders of magnitude: development multiplies a latent-image speck by of order 10⁷ to 10⁸, and nothing in Parts XXI to XXV does anything of the kind.
• What is the image substance, chemically? A pigment, developed silver, printed-out silver, a noble metal — four different answers among seven processes.
• What does the “developer” do, where there is one? In a kallitype it reduces; in a palladium print it dissolves and reduces nothing; in the New Cyanotype’s acid bath it strips ligands off iron(II) that light already made. Three baths called developers doing three different things is the single most useful thing in this field.
• What does the fixing or clearing step remove, and what happens if it is left out? Unreacted silver halide, residual iron, or unreduced metal salt — and the consequences differ from a stain to a self-destroying print.

Field six — permanence

What are you prepared to claim for each print, and on what evidence? Every sentence classified.

Three classes of claim, and how to mark them

1. Measured — you did it, with an instrument, and you can state the precisionExample: "The masked margin of the palladium print showed no yellow under a bluish light after the third clearing bath." That is a check you performed and it is the single best predictor of that print's futureyours
2. Published — a named source says it, and you cite the sectionExample: "Palladium metal is chemically inert under normal storage and display conditions." That is Ware and the AIC, about the substance, and it is not a claim about your print's paper
3. Inferred — you reasoned it from something published or measured, and you say soExample: "Since my palladium print was cleared by the EDTA and sulfite sequence, which Ware reports produced no stain under accelerated ageing, I expect it to be more stable than a print cleared in one bath." That is an inference from a study on other prints to yours, and marking it as one is the whole disciplinereasoned

A row in which every permanence sentence is marked is more useful than one in which the claims are stronger. The marking is the contribution.

Three things not to write, for the reasons the cost and permanence lesson sets out: a lifetime in years, “archival” (IPI’s own warning is that it is a marketing term, neither standardised nor legal), and a permanence claim about platinum on a print that is palladium.

And where you have run a test, say which. A residual-thiosulfate test on a fixed silver print, a masked-margin inspection on the iron processes, a wash test — these are the sentences with real predictive value and they belong at the top of the field.

Field seven — cost

Consumables per print, from your own records, dated, with the assumptions stated.

C = (Σ quantity used × unit price) ÷ prints made

Consumables per print

Two rules make the figure usable. Count what one print consumed, not what you bought — a jar of silver nitrate is capital that lasts many sessions, and what belongs in the row is the fraction one print used. And name every item you could not price, rather than dropping it: the subtotal is then a floor and you say so, which is exactly what every practical page in this course does.

Where your data will be better than the course’s. The price file’s cost column for the matrix is empty for the kallitype, the Van Dyke and the palladium print, in each case because the iron and noble metal salts are unpriced. If you bought them, you have the figure the course does not, and it belongs in your report with the date and the supplier.

Field eight — difficulty

The field most atlases omit, and the one a beginner most needs. Report three things per process, from your own record:

• Failure rate. Sheets coated against sheets you would show. Not an impression: a count.
• Session length. Wall-clock time from setting out to the print on the drying screen, including the waiting.
• What actually went wrong, named. Not “it was tricky” — a coating that mottled because the plate was not level, an exposure guessed because the test strip was cut too short, a clearing bath at capacity.

Then rank the seven by difficulty and say what your ranking rests on, because a failure rate depends on the printer as much as on the process, and yours is a beginner’s failure rate on a process you have made three or four times. Say that too. It is the most honest number in the assignment and the most useful one, precisely because nobody publishes it.

The accessibility route

A student who cannot make every process completes the rows they can and uses the course’s own published data for the rest, clearly marked as not their own measurement.

That marking is the assignment rather than an apology for it. A row that says measured by me, 12 October, Part XV densitometer, ±0.02 beside a row that says published: Ware, Platinomicon §11.6, print-out sensitiser on a different paper is a more honest document than seven rows of numbers with no provenance, and it is the discipline field six asks for anyway.

What to do, process by process:

• No palladium? Use the palladium-toned kallitype instead and label the row as such — it is a different object and the cost lesson says how. Or take the published palladium figures and mark them read.
• No darkroom for the silver gelatin row? Take Part XIII’s published paper curve and mark it, and say which of your own processes you used as the reference against which ratios were computed.
• No albumen? It is the most laborious of the seven and the one most often dropped. The atlas entry and the Getty’s description carry what you need to fill the row as published.

What you must not do is fill a row from a description and present it as a measurement, or leave a row blank without saying what is missing. The matrix the course publishes has three deliberately empty cells, each carrying a sentence saying what is missing for that subject, and they are the most useful cells in it.

The written argument

Which process would you use for which picture, and why — in terms of the fields you measured.

Two thousand words is plenty. What makes it a good piece of work is that every claim points back at a number or an observation in your own table. Three shapes of argument that work:

From tonal scale to subject. “This image has its information in the high values and almost nothing below mid-grey. My palladium row shows an exposure scale of 2.2 with a mid-tone slope of 0.8 and a substantial toe; my cyanotype row shows 0.9 and a slope of 1.6. The palladium print separates the light tones the picture is made of, and the cyanotype compresses them into three steps.” That is an argument.

From surface to subject. “The picture is about the texture of a wall. Six of my seven prints put the image in the paper’s own surface and one puts it under a gelatin layer on baryta. Held in raking light at 15 degrees, only the silver gelatin print shows a surface that is not the paper’s.”

From cost and difficulty to a decision. “My failure rate in palladium was two sheets in five and in kallitype one in six, and the metal in a failed palladium sheet is about 40 mg. For a print I intend to make once, that is a defensible cost; for a variable edition of ten it is not, and the honest answer for that job is a kallitype toned in palladium.”

And one argument to avoid. “It should be printed in platinum because platinum is the finest process.” You did not print platinum, prestige is not a field in the table, and the cost lesson gives the test to apply instead: name the quality of this image that this process serves, in terms of tonal scale or surface, and if the honest answer is “it will look expensive”, print it in silver.

How this feeds the capstone

The capstone specification requires an alternative-process print and a comparison, and both come from here. The print is one of the seven, chosen on the argument you just made rather than on availability; the comparison document is the completed table.

Keep the set together and keep it well: mounted or interleaved in materials passing the Photographic Activity Test, on the AIC’s own environmental terms for the noble-metal print — about 20 °C with not more than 2 degrees of drift, and 50 per cent relative humidity varying by not more than 5 per cent over 24 hours. The Library of Congress note the general reason: adverse environments make paper yellow and brittle, especially where the paper is acidic, and several of these prints have acid in them by design.

And re-read the set in a year. Same light, same instrument, same reference. Seven prints from one negative with recorded densities and a date on the back is a comparative ageing experiment the course does not have, and it costs nothing but the drawer.

The record required

For every print, whether or not it went into a row:

Field
Process, and the page you worked from
Date, session length, room temperature and relative humidity
Negative: which, its density range, and — if a matched set — the correction curve applied
Paper: maker, name, weight, sizing, buffered or not
Sensitiser: formula, batch, strength, volume, coating method, coverage in cm³/m²
Exposure: source, distance, dose or time, and the conditions if in sunlight
Processing: every bath, its strength, its temperature, its time and its age
Clearing or fixing check performed, and its result
Density readings, wet and 24 hours dry, with instrument precision
Colour signal, green and blue, on a stated patch
Surface observation, with the raking-light geometry
Outcome: shown, kept, or failed — and if failed, why

What to submit

1. The prints, all seven rows’ worth, from one image, presented together, with the failures kept and labelled rather than thrown away.
2. The seven curves on one pair of axes, with the measurement method, its precision and its limitations stated on the figure or beside it.
3. The completed atlas rows, eight fields each, every claim marked measured, published or inferred, and every unfillable field carrying a sentence saying what is missing.
4. The written argument, matching processes to pictures in terms of the measured fields.
5. The full record above, for every sheet including the failures.

📓The one paragraph the whole assignment turns on

Whatever else you write, write this: which negative strategy you took — one compromise negative or a matched set — and what it cost your comparison.

If you took the compromise negative, some processes were printed from a negative that did not suit them and their rows understate what they can do; say which and by how much, from the gap between the negative’s density range and each process’s measured exposure scale. If you took the matched set, your negatives were not identical, so a difference between two prints may be a difference between two correction curves; say so, and publish the curves.

A comparison whose confound is stated is a comparison. One whose confound is silent is a set of pictures.

Recap

One negative, seven processes, eight fields, one observer, one instrument, one day where possible. The comparison is the point and everything held constant is what makes it one. The published literature does not contain this measurement, the course’s own matrix says so in its scope, and three of that matrix’s cost cells are empty for want of prices you may well have on a receipt.

Measure the tonal scale rather than describing it. Record surface and colour by stated methods with stated limits. Express speed as a ratio. Write the mechanism in your own words, and get the three different meanings of the word “developer” right. Classify every permanence sentence as measured, published or inferred. Cost from your own records and name the gaps. Report your failure rate as a count.

And say, in the first paragraph, which negative strategy you chose and what it cost you.

Check your understanding

Question 1. Ware gives the classic cyanotype an exposure scale of about 0.9 and print-out palladium about 2.4. What follows for a single-negative comparison?

• Nothing; exposure scale describes the print, not the negative
• A negative that suits one will not suit the other by more than a stop and a half of density range, so either the negative is a compromise that penalises both ends, or a matched set is made from one image — and the assignment requires you to say which you did and what it cost
• The cyanotype needs the longer-scale negative, because a shorter scale needs more density to fill it
• Both will print correctly from any negative, since exposure time compensates

Show the answer and why

Answer: A negative that suits one will not suit the other by more than a stop and a half of density range, so either the negative is a compromise that penalises both ends, or a matched set is made from one image — and the assignment requires you to say which you did and what it cost

Exposure scale is the range of log exposures the process can render, so it is exactly a statement about what the negative must carry — which is why option one is wrong and option three has the relationship inverted: a longer scale asks for a longer negative. Option four confuses exposure with contrast; more time moves the whole print along the curve and does not change how much range the curve spans. The honest handling of the conflict is the substance of the assignment rather than an obstacle to it.

Question 2. You report an image colour as "green-minus-blue density difference of 0.14 on my Part XV head". What is that claim good for?

• Comparing your seven prints with each other, and nothing else, because the number is defined by your own instrument's spectral conditions rather than by any colorimetric standard
• Comparing your prints with published CIELAB values for the same processes
• Nothing, since a densitometer cannot detect colour
• Establishing the hue in the conservation literature's vocabulary without a side-by-side comparison

Show the answer and why

Answer: Comparing your seven prints with each other, and nothing else, because the number is defined by your own instrument's spectral conditions rather than by any colorimetric standard

A density is fully defined only by its geometric and spectral conditions, and yours are a pair of LEDs. Within your own set the number is reproducible and moves when the hue moves, which is exactly what a comparison needs; outside it, it means nothing. Option four is the other half of the method and cannot be got from the number: the conservation vocabulary is assigned by laying prints side by side under one light, not by reading an instrument.

Question 3. Which permanence sentence is correctly classified?

• "Measured: palladium is chemically inert and will not fade."
• "Published: the masked margin of my print showed no yellow under a bluish light."
• "Inferred: because my palladium print was cleared by the EDTA and sulfite sequence, which Ware reports produced no stain under accelerated ageing of other prints, I expect it to be more stable than one cleared in a single bath."
• "Measured: this print will last at least 200 years."

Show the answer and why

Answer: "Inferred: because my palladium print was cleared by the EDTA and sulfite sequence, which Ware reports produced no stain under accelerated ageing of other prints, I expect it to be more stable than one cleared in a single bath."

Option three moves correctly from a published study on other prints to a statement about this one, and marks the move. Options one and two have their labels swapped — the inertness of palladium is a published property of a substance and the masked-margin inspection is something you did — and that swap is the commonest error in this field, because it makes a general claim sound personal and a personal check sound authoritative. Option four is not a classification error but a claim nobody has established for any photographic object.

Question 4. Why does the assignment insist on a count for the failure-rate field rather than a description?

• Because a count is easier to mark
• Because it is the field that no published atlas fills, so a stated count with the stated caveat that it is a beginner's rate on a process made three or four times is genuinely new data — and an impression cannot be compared between processes or between people
• Because failure rate determines the cost per finished print, and nothing else does
• Because a description would reveal which processes the student found hard, which is not relevant

Show the answer and why

Answer: Because it is the field that no published atlas fills, so a stated count with the stated caveat that it is a beginner's rate on a process made three or four times is genuinely new data — and an impression cannot be compared between processes or between people

The whole assignment is built on holding things constant so that differences mean something, and an impression cannot be held constant even within one person's report. Option three states something true but partial — failure rate does multiply the consumables cost per finished print, which is why the cost lesson says to budget for it — but the reason the field exists is that it is the one useful thing about these processes that nobody publishes. Option four inverts the purpose: which processes you found hard, and why, is precisely the information a beginner reading your row needs.

Question 5. A student prints six processes and fills the seventh row from Ware's published palladium figures. What must their row do to be acceptable?

• Nothing special; published data and measured data are equally valid
• Mark the row as published rather than measured, cite the source and section, note that Ware's figures are for a print-out sensitiser on his own paper under his own lamp, and state which of their own processes served as the reference for any ratios
• Omit the row entirely, since an unmeasured row invalidates the comparison
• Estimate the palladium figures from the kallitype row, since both are iron processes

Show the answer and why

Answer: Mark the row as published rather than measured, cite the source and section, note that Ware's figures are for a print-out sensitiser on his own paper under his own lamp, and state which of their own processes served as the reference for any ratios

Marking is the whole discipline, and the third clause matters as much as the first: Ware's palladium curves are of the print-out ammonium system rather than the develop-out route the labs teach, so a reader who takes them as equivalent has been misled by an unmarked substitution. Option three is the opposite failure — the course's own matrix leaves three cells empty on purpose, each with a sentence saying what is missing, and calls them its most useful cells. Option four invents a number, which is the one thing no field in this table may contain.

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