Cost, Permanence and When a Platinum Print Earns Its Price

Somebody will tell you that a platinum print lasts a thousand years. Two things are wrong with that sentence and neither is the thousand.

The first is that it is a claim about the wrong object. Platinum and palladium are chemically inert under any condition a photograph will meet, and nothing in the ordinary environment attacks them. What will fail is the sheet of cellulose the metal is sitting in — and the process that put it there left that sheet acidic. The second is that most prints sold as platinum are not platinum, so the claim has been transferred from one metal to another without anybody checking which is in the paper.

This page does three things. It works out what the metal in one print actually weighs, because that is a number the course can compute exactly and a price is a number it currently cannot. It examines the permanence claim against the conservation evidence, sentence by sentence, and says which sentences a photographer may honestly write on the back of a print. And it argues the accessibility question in full rather than leaving it as a footnote, because a part that costs this much has to answer for itself.

The cost arithmetic, done properly

The chain is short and every link is sourced. Start from the metal in the bottle and end at a mass on a sheet.

c(mixed) = c(stock) ÷ 2

Palladium in the mixed sensitiser

because the coating lab mixes equal volumes of iron and metal solution, and that ratio is the stoicheiometry rather than a convenience. Ware’s standard palladium stock is 0.5 M in Na₂PdCl₄, so the sensitiser that reaches the paper is 0.25 M — 0.25 mmol of palladium per millilitre.

V = A × v

Sensitiser used on one sheet

with A the coated area and v the specific coating volume. Ware’s working range is 24 to 36 cm³/m², and his own guide is 1.4 to 1.5 cm³ for a 10 × 8 inch print coated by rod. Brush coating consumes more, and he calls it expensively wasteful.

m = V × c(mixed) × M

Palladium applied per sheet

with M the atomic mass of palladium, 106.4 g/mol.

🧮One 8 × 10 print, in milligrams of palladium

Ware states the area of an 8 × 10 inch print as 21 × 26 cm, which is 0.055 m² — a little more than the 0.052 m² of the bare 8 × 10 rectangle, because the coated area runs slightly outside the negative.

1.5 mL × 0.25 mmol/mL = 0.375 mmol

Rod coating, at Ware's own guide

0.375 mmol × 106.4 mg/mmol = 40 mg of palladium

As a mass of metal

2.3 mL × 0.25 mmol/mL × 106.4 = 61 mg

Brush coating, at a kit's own drop table

Ware’s own independent figure agrees. He states coating weights of 6 to 9 millimoles of metal per square metre, which on 0.055 m² is 0.33 to 0.50 mmol, or 35 to 53 mg. Two routes to the same answer — one from a molarity and a volume, one from his stated coating weight — landing within about 20 per cent of each other, is as good a check as this material offers.

So: roughly 40 mg of palladium on an 8 × 10 print by rod, and about half as much again by brush. At 4 × 5 inches it is about a quarter of that; at 16 × 20 it is about four times.

And what it is not. This is the metal applied, not the metal deposited. What is not reduced washes out in the clearing baths, and Ware’s X-ray fluorescence work shows the reduced fraction varying with exposure. The applied figure is what you spend; the deposited figure is what you keep, and the difference is why the spent first clearing bath is worth saving.

!Why this page gives you a mass and not a price

src/data/prices.json holds no price for any platinum or palladium salt, for ferric oxalate, for potassium oxalate, for EDTA, or for unbuffered cotton paper in the sizes this part prints at. It names all five as gaps, and the entry for the palladium salt is written in this page’s own terms, down to the milligrams of metal an 8 × 10 carries. A recorded gap is not a price. This is still the most consequential missing figure in the course, and naming it is the most the file can do.

What that means for you: the arithmetic above is complete and dated in every term except the last, and the last term is a market price that changes weekly. Do the multiplication yourself, on the day, with the listing in front of you, and write the date beside the answer. That is what the course would have to do anyway, and doing it yourself is more honest than reading a figure that was true in September 2026.

cost per print = m × (price per gram of palladium metal in the salt you buy, on today’s date)

What you can finish that the course cannot

Two traps in that last term. A supplier prices the salt, not the metal: sodium tetrachloropalladate(II) is 294.19 g/mol anhydrous against palladium’s 106.4, so a gram of the anhydrous salt carries about 0.36 g of palladium, and the trihydrate at 348.3 g/mol carries about 0.31 g. And a made-up solution is priced by volume: a 15 per cent w/v solution holds 15 g of salt, and therefore about 5.4 g of palladium, in every 100 mL.

Where the rest of the money goes

Six items, and the metal is not the whole of it.

Paper is the second cost and it is not small. Ware’s list of unbuffered papers runs from handmade Ruscombe Mill sheets to Hahnemühle Platinum Rag, and Part XXI’s own dated citation put the last of those at £23.95 for twenty-five 8 × 10 sheets on 6 September 2026 — about 96p a sheet, before you spoil any. On a cyanotype that is the dominant cost; here it is roughly comparable with the metal, which is the inversion this whole part turns on.

Ferric oxalate is cheap per print and expensive per bottle, and it is the one that goes off. Ware records six to nine months in the dark as the keeping figure “said by some”; Bostick and Sullivan give about a year. A bottle bought for one session and used for one session has cost you the whole bottle.

The developer is effectively capital rather than consumable. It is reused for years, replenished for evaporation, filtered for sludge. Bostick and Sullivan call its life indefinite.

The clearing chemicals are cheap and have published capacities, which is unusual enough to be worth using: Ware gives about 50 to 60 prints of 10 × 8 in per litre for the first EDTA bath and about 100 for the third, and his whole published batch of processing chemicals is stated as sufficient for about sixty prints. That is a real per-print figure, and it is small.

And the sheets that fail are a cost line rather than an embarrassment. A beginner’s failure rate on this process is not published anywhere the course could find, and it is the field the comparison atlas asks you to fill from your own record precisely because nobody else fills it. Budget for it: if one sheet in three fails, your metal cost per finished print is half as much again as the arithmetic above.

What one 8 × 10 palladium print consumes, ranked by cost rather than by volume

from dominant to negligible

1. Palladium — about 40 mg by rod, about 60 mg by brushThe only item whose price the course cannot supply, and the one that decides whether the part is affordable. Rod coating rather than brush is a saving of about a third, every sheet, for the price of ten minutes' practiceunpriced
2. Paper — one sheet, about 96p at a dated 2026 UK listingUnbuffered, 100 per cent cotton, from Ware's own list. The figure is Part XXI's citation of a retailer rather than a planner price, and the same listing was shown out of stock on the day
3. Ferric oxalate — about 1 mLCheap per print; the cost is the bottle's keeping time rather than its volume
4. Clearing chemicals — about a fiftieth of a litre of bath 1, a hundredth of bath 3Published capacities, small quantities, ordinary solids
5. Developer — a fraction of a reused litreEffectively capital. It changes rather than exhausts, and printers argue about whether it improves
6. The sheets that failed — however many that wasThe line nobody publishes, and the reason the atlas asks you to record your own failure rateyours to measure

The ranking is the course's, from the arithmetic above and the one dated paper listing it holds. Everything below the second row is small enough that changing it will not change your decision.

Why palladium first

Three reasons, and only the first is about money.

Price. Ware’s own summary of contemporary practice: it is very much easier and less expensive to print in palladium than in platinum, very few practitioners today even attempt pure platinum, and most use palladium alone or a mixture in which palladium predominates. That is a statement about a market rather than about a metal, and it can invert — in the 1890s palladium was dearer than platinum, at 6 pence a grain or about £12 an ounce against about £2 an ounce for platinum, which is exactly why Willis did not use it until the war made him.

Chemistry. Palladium is the easier metal and not the cheaper compromise. More of it is aquated at sensitiser strength — the equilibrium constant is 0.17 against platinum’s 0.015 — so it reduces faster, and Ware’s summary is that palladium “is faster to print and achieves a finer, smoother quality than platinum under a wider range of conditions and paper choices.”

And safety, which is the ruling this course actually applied. The 4 September 2026 decision that students perform palladium and never handle platinum rests on H334 and on an exposure limit 2,500 times tighter for the compound than for the metal; the chemistry lesson carries the argument. What is worth saying here is that the substitution turns out to be a better process as well as a permissible one, which is a happier position than most substitutions reach — and that a course which had only the price argument would have made the same choice for a worse reason.

The cheaper routes, compared honestly

Three of them, and each keeps something different.

Four ways to a matte, long-scale, warm-toned print

1. A palladium print — the object this part makesInert noble metal among bare paper fibres, no binder, matte, exposure scale about 2.4 on Ware's own densitometry, maximum density about 1.45. About 40 mg of palladium a sheet. What it keeps: everything. What it costs: the metal, and a process with no forgiving steps
2. A palladium-toned kallitype — the course's stated accessibility routeA silver image made by the same iron chemistry on the same paper with the same rod, then plated with palladium. Bostick and Sullivan build the toner from 7 to 15 drops of palladium solution in a litre of 1 per cent citric acid, and 10 mL of their solution is 255 drops — so a whole litre of toner uses about 0.3 to 0.6 mL of palladium, against about 1 mL for one coated sheet. What it keeps: the surface, the scale, the craft, and a real noble metal on the image. What it gives up: the image is silver plated with palladium rather than palladium, and the permanence argument is different in kind
3. A well-made silver gelatin print on a warm-tone paperPart XVIII and Part XIX own it. What it keeps: tonal control the alternative processes cannot approach — a grade, a filter, dodging, burning, a second attempt at no cost. What it gives up: the surface. A gelatin layer on baryta is a different object from metal in paper, and no toner makes one into the other
4. A gold-toned salted paper printPart XXII owns it. What it keeps: printing-out, an image in the fibres, and a genuinely permanent noble metal doing the protecting. What it gives up: the colour range is the salt print's rather than palladium's, and the image substance underneath is still silver

Every route here is one the course teaches. The comparison is of what each object is, and the assignment that closes this part asks you to make it from your own prints rather than from this table.

⁇Is a palladium-toned kallitype comparable in permanence to a palladium print?

The course recommends it as an accessibility route, so the question has to be answered rather than assumed, and the honest answer is no source read for this course establishes it.

What is established. Toning a colloidal silver image with a noble metal is a permanence treatment rather than a colour one, and the toned kallitype atlas entry carries the mechanism: a printed-out or lightly developed silver image is nanoparticulate, so its surface area relative to its mass is enormous, which makes it a conspicuous target for anything that attacks silver — and a coating of gold or palladium protects it.

What is not established. No study read for this course compares the ageing of a palladium-toned kallitype with that of a palladium print. What can be said from the chemistry is that the two objects are different: one is an image of palladium, the other an image of silver with palladium on it, and the protection in the second depends on how completely the plating covers the silver — which nobody has measured for this bath.

And one relevant warning does exist, pointing the other way. Ware notes that palladium itself “is not as resistant to chemical attack as platinum, and may therefore be less permanent archivally, especially if chemical treatments are later applied to the print.” So even the unqualified palladium print is a step below platinum on his own reading.

What the course states. The palladium-toned kallitype is a legitimate route to the craft, the surface and most of the learning of this part at a small fraction of the cost, and the course recommends it on those grounds. It is not offered as an equal-permanence substitute, and a student who takes it should say so on the atlas row rather than filling the permanence field from this page.

The permanence claim, examined

Take it apart into four separate claims, because they have four different evidence bases and only one of them is strong.

Four claims, ranked by how well the evidence supports them

1. 1The image substance does not deteriorate — strongly supportedPlatinum and palladium are chemically inert under any condition a print will meet: no fading, no oxidation, no sulfiding. Ware's own statement for palladium prints is that they are highly lightfast, may be displayed under good lighting, and are robustly resistant to all contaminants likely to arise in a normal environment. The AIC calls both metals robust, permanent media
2. 2Prints from the 1880s survive with their images intact — supported, with a stated populationThis is an observation about surviving objects in institutional collections, made by conservators. What it is not is a random sample: prints that were destroyed are not in the collections, and the population is the prints that were made well, kept well and thought worth keeping. That is a real bias and it points in the flattering direction
3. 3The paper will fail before the image does — supported, and it is the finding that mattersWare: the metal is quite invulnerable and its paper substrate is certainly not; acidic embrittlement of the cellulose is the chief besetting problem historic platinotypes present to the conservator. The AIC records it from the bench: supports become brittle from the acidic processing and yellow, and cracks, breaks and broken corners are common
4. 4The metal itself catalyses the destruction of the paper — one preliminary experiment, marked as such by its own authorThe evidence and its limits are in the chemistry lesson. What belongs here is the consequence: even if the catalysis is real, the acidity the process leaves in the sheet is the better-established cause, and it is the one a printer controls

And there is a fifth claim that is usually made silently: that these are prints of platinum. The Getty records that only after 1917 did photographers begin to use palladium and then platinum-palladium mixtures on paper they coated themselves, so most prints made before the First World War are simple platinotypes — but the “Pt/Pd print” of a modern portfolio is a mixture, and Ware’s X-ray fluorescence work shows that a sensitiser mixed 1:1 deposits far more palladium than platinum, starting near 1:3 at low exposures. If most prints sold as platinum contain more palladium than platinum, a permanence claim made for platinum has quietly become a claim about a different metal. The course states that as a question and does not answer it. What an honest label says is which metal made the image, and in what proportion.

=Three documented cases of a noble-metal print changing

The inert-image claim is about chemistry, and objects live in the world. These three are on record and they are the reason the claim needs its qualifications.

Densities that went up. Douglas Severson discovered in 1984, by careful monitoring of a Stieglitz palladium print in the Art Institute of Chicago sent to Japan for exhibition, that on its return the optical densities had increased by 30 per cent in the mid-tones and 15 per cent in the shadows. Ware records the cause as uncertain: light levels at the venue may have been high, and it is suspected the work met an outside atmosphere with a high moisture content in transit.

Prints that were cleaned and may have re-yellowed. Steichen treated a set of Stieglitz’s palladiotypes, and Ware records “a growing suspicion” that they have since re-yellowed, complicated by the belief that many of the prints had been waxed and that the wax was removed and not necessarily replaced. He notes the evidential problem plainly: there are no photographs for comparison, a few untreated Stieglitz palladiotypes exist that could serve as controls, and the judgement so far rests on visual memory.

Prints that mirror. The AIC records a 2014 X-ray fluorescence confirmation that platinum prints can mirror in maximum-density areas — the same phenomenon as silver mirroring, on a metal that is not supposed to do anything.

None of these overturns the inert-image claim. All three say the same thing about how to use it: the claim is about a substance, and a print is an object.

⚗The residual-iron evidence, which is the part a printer controls

This is the one where the printer’s own decisions decide the outcome, so it is the one to act on.

Matthew Clarke and Dana Hemmenway processed platinum and palladium test prints four ways — long clear and long wash, long clear and short wash, short clear and long wash, short clear and short wash — and aged them at 70 °C and 75 per cent relative humidity in the dark for four weeks. Four findings, and the second is the one that should change your practice:

1. In the worst category of short cuts, residual iron was significantly raised, and more so for palladium than for platinum.
2. All the specimens showed little or no visible stain immediately after preparation and would have been judged acceptable as artists’ prints.
3. After ageing, yellow stains appeared that correlated with the measured residual iron and closely resembled the staining seen in historical platinotypes.
4. The stain did not require any platinum salt: ferric oxalate alone gave similar results, and papers sized with gelatin retained more iron than those sized with alum and rosin.

The Getty adds the analytical ceiling: even after the best fixing and clearing procedures, enough iron remains in a platinotype to be detected by X-ray fluorescence at the iron K-alpha line at 6.40 keV, at different concentrations in the maximum and minimum density regions.

And Ware’s comparison of methods is the reason this course specifies the sequence it does: he recommends a reducing agent together with a modern chelating agent in place of hydrochloric acid, and reports that artificially accelerated ageing of prints cleared that way “has been shown to produce no stain”.

So the permanence of your print is decided in the third clearing bath, on the evening you make it, by a difference you cannot see at the time. The troubleshooting entry for the stain is where the fault is diagnosed once it has appeared.

Storage, mounting and display — and where the rules differ

The general guidance is the general guidance, and this family has three specific departures from it.

The environment. The AIC’s figures for platinum, platinum-palladium and palladium prints are 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, in good quality, neutral pH paper-board folders, protected from light, dust and handling.

Materials must pass the Photographic Activity Test. The AIC specifies it and IPI explain what it is: ISO 18916, using a detector that screens for the oxidation and reduction reactions that cause image fade, silver mirroring and red or gold spots — with the warning that “acid-free”, “archival”, “museum-quality” and “conservation board” are marketing terms that are neither standardised nor legal. A label is not a test.

Departure one: this print’s neighbours matter more than most. The AIC records that a platinum print stored in contact with paper for a prolonged period can discolour the facing sheet and transfer a mirror image to it — the phenomenon Ware calls autoplatinography, whose chemistry remains unresolved after a NARA investigation in 2013–14 that eliminated most of the simple explanations. Interleave. And note that the same investigation found untoned silver prints on specialist papers doing it too, so it is not a reason to treat a platinum print as uniquely dangerous to its album.

Departure two: be careful what you deacidify. The AIC’s caution is specific — be cautious of using strong de-acidification processes unless pure platinum content is confirmed, because they can be deleterious to a silver-platinum print. Willis’s Satista and the “faux platinum” silver papers are exactly the objects that look like the ones the treatment would suit.

Departure three, and it is the one that will surprise a reader coming from Part XXI: the mount rule is the opposite way round. A cyanotype must not go on a buffered mount, because an alkaline reserve destroys Prussian blue — Ware’s arithmetic on ISO 9706 puts a permanent paper’s reserve at an eightfold molar excess over the iron in a siderotype coating, and a saturated calcium carbonate solution sits at a pH that decolourises the pigment irreversibly. A palladium image is indifferent to alkali. What it is not indifferent to is the acidity in its own paper, which is why Ware’s clearing sequence deliberately ends in an alkaline bath that leaves the sheet in “a beneficial alkaline condition”. The conservation recommendation is nonetheless a neutral pH board rather than a buffered one, and the course follows the conservators rather than reasoning from the chemistry: the mount is protecting a paper object, not the image.

And the general environmental argument still applies. The Library of Congress note the mechanism that Ware’s catalysis chapter elaborates: adverse environments make paper yellow and brittle, especially where the paper is acidic, and air pollution produces nitric and sulfuric acids that attack all components of photographs and make supports discolour and become brittle. A brittle print gets a stiff card support beneath it and is not rolled.

Permanence as an argument rather than a slogan

Here is the practical form of everything above. Three sentences a photographer may honestly write on the back of a palladium print, and three they may not.

May write:

• “The image substance is metallic palladium, which is chemically inert under normal storage and display conditions and will not fade, oxidise or sulfide.” Published, and about the right object.
• “The print was cleared in three baths — disodium EDTA, sodium sulfite, tetrasodium EDTA — and the masked margin showed no yellow under a bluish light.” Measured, by you, and it is the sentence that actually predicts the print’s future.
• “The paper is [named paper], unbuffered 100 per cent cotton, and the print was left in an alkaline condition by the final clearing bath.” Measured and material.

May not write:

• “This print will last a thousand years.” Nobody has established a lifetime for any photographic object, and the claim attaches a number to a process that has no number.
• “Platinum prints are permanent.” Wrong object, and possibly wrong metal. What is permanent is the image substance; what will fail is the paper; and if the sensitiser was mixed, the image may be mostly palladium.
• “Archival.” IPI’s own warning covers it: the word is a marketing term, neither standardised nor legal. Say what was done instead.

The rule underneath all six: classify every sentence as measured, published or inferred, and let the reader see which is which. That is the discipline the atlas assignment will ask you for in its permanence field, and this is where it is learned.

What this process does to a picture

The art-track question, and the answer has to be in terms of what the process actually does rather than what it costs.

A long scale with a shallow slope, which suits a subject with information in the high values. Ware’s own figures give palladium an exposure scale of about 2.4 with a mid-tone slope of about 0.78, and he attributes the extra length to a substantial non-linear toe. Read that as a photographer and it says: this process spends its gradation on the light tones. A subject with delicate, closely spaced high values — mist, skin, plaster, snow with texture in it, white on white — gets separation here that a grade-2 silver paper compresses. A subject whose interest is a deep, clean black does not: maximum density is about 1.45, well under a glossy silver gelatin print’s, and no amount of exposure changes that.

A surface that is the paper’s own. No gloss, no layer, nothing between the eye and the fibres. That suits a picture that wants to be looked into rather than at, and it makes the paper a compositional choice rather than a substrate. The IPI’s own historical note is that platinum was “exalted as being more artistic and beautiful than other printing processes due to the softness and subtlety of tone it offered”, which is a nineteenth-century judgement recorded by a twenty-first-century conservation body and is worth reading as evidence about taste rather than about physics.

And a colour you choose before the exposure rather than after it. Humidity, developer and temperature are all committed before or during the process, not applied to a finished print. That is a different way of working from toning, and it rewards a printer who has decided what they want.

Which subjects use those qualities rather than merely displaying them? The AIC’s list of historic practitioners is the evidence base for any answer: Manuel Álvarez Bravo, Alvin Langdon Coburn, Imogen Cunningham, Edward S. Curtis, Peter Henry Emerson, Frederick H. Evans, Laura Gilpin, Frederick Hollyer, Alfred Horsley-Hinton, Gertrude Käsebier, Irving Penn, Edward Steichen, Alfred Stieglitz, Paul Strand, Edward Weston, Clarence H. White. What that list is evidence of is who used the process, and nothing more. It is a conservation wiki’s roll of names, not an argument that their pictures needed it, and this course will not manufacture one. Ware’s chapters on Stieglitz, Strand and Penn document what those three did with the process in technical detail — Penn’s heavy coating and six-to-ten-hour clearing, Strand’s request that the Platinotype Company add a coating to make Warm Black Japine — and that is the level at which an evidence-based statement can be made.

The test to apply to your own picture is the one the comparison atlas will make you write down: 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.

The accessibility argument, in full

A student who cannot afford the metal has not been excluded from this part, and here is exactly what they can do.

Six of the eight pages need no palladium at all. The chemistry lesson, this page, the Level D lesson and the overview are reading. The two labs and the experiment are the palladium pages, and the assignment is completable with a marked row.

The two labs are runnable on a substitute. Everything in the coating lab except the metal itself — the drop calibration, the paper choice, the humidity control, the levelling, the rod technique, the coverage arithmetic — can be rehearsed with a cyanotype sensitiser at a few pence a sheet. Everything in the printing lab — the exposure calibration, the three-bath clearing, the masked-margin inspection, the wash — runs unchanged on a kallitype, because it is the same iron chemistry with silver in the metal’s place.

The experiment is runnable in full on kallitype. Humidity, developer, oxidiser dose and coating weight are the same four variables on the same iron photochemistry. What you cannot measure is palladium’s own curve.

And the atlas row can be filled honestly without a palladium print, by using the course’s own published data and marking it as not your own measurement. That marking is not a penalty; it is the same discipline the page asks of every claim.

What you actually lose, stated plainly. You will not have measured this process’s exposure scale yourself, you will not have seen what double-coating does to maximum density, and you will not own an object made of an inert noble metal. Those are real losses and the course does not pretend otherwise. What you will have is the chemistry, the craft, the record and a defensible comparison — which is most of what this part is for.

A middle route exists and it is cheap. Print at 4 × 5 inches. A quarter of the area is about a quarter of the metal — roughly 10 mg a sheet rather than 40 — and Bostick and Sullivan’s own remark is that small negatives make beautiful jewel-like prints. Every measurement in this part works at that size.

The environmental and waste argument

Noble metals are mined at real cost, and a course that spends them by the milligram should say so rather than treating the bottle as a photographic supply like any other. This is the one part of the course where the material’s provenance is a moral question as well as a budget line, and the honest position is that the course has no life-cycle data and is not going to invent any.

What the course can say is what happens to the metal you buy. Some of it becomes the image; some of it washes out in the first clearing bath. Ware’s own instruction for that bath is unambiguous — when spent, save it for recovery of precious metal — and commercial printers keep spent developer for the same reason, filtering off the sludge that accumulates as the bath darkens.

Is recovery practical at a student’s scale? The honest answer is that no source read for this course establishes that it is. The arithmetic gives the shape of the problem: one 8 × 10 sheet applies about 40 mg of palladium, an unknown fraction of which stays in the print, so a year’s printing at one sheet a week puts of the order of a gram of palladium into a few tens of litres of dilute solution. That is a quantity worth recovering industrially and a concentration that makes recovery at home a chemistry project in its own right, with its own hazards, that this course does not teach.

What the course therefore states as its position. Collect every noble-metal-bearing solution in one labelled container across the whole part, do not put any of it down a drain, and dispose of it once, through a licensed hazardous-waste route rather than through a recovery attempt. The palladium salt carries H400 and H410 — very toxic to aquatic life with long lasting effects — in about three-quarters of its notified reports, and that alone settles the drain question. What may lawfully be done with it, and what a licensed route looks like, differs between jurisdictions and changes. Check your local regulations; they govern. See the disposal ruling.

The historical form of the same argument

It is worth knowing that the economic decision you are making now is the decision that shaped the process itself, and that it went the other way twice.

Platinum was cheap and then it was not. Willis’s first commercial papers went on sale in Britain in 1879 at a shilling for a demy sheet of 17¾ × 22¾ inches — about fourpence a square foot. Then Ostwald discovered in 1902 that platinum catalyses the oxidation of ammonia to nitric acid; nitric acid makes explosives; and photography lost its claim on the metal. Germany banned its photographic use as early as 1901 on account of lamp filaments. By 1916 the British government had embargoed it for anything but munitions, and Ware’s price series has the metal peaking in 1920 at 800 shillings — £40 — per troy ounce, five times the 1900 price, before falling in the Depression to 93 shillings in 1931.

And palladium was the expensive one first. In the 1890s palladium toning of silver prints was acknowledged in the manuals and dismissed as impractical because palladium was much more costly than platinum — 6 pence a grain, about £12 an ounce, against about £2 for platinum. It became the substitute only when the war made platinum unavailable at any price, and Willis launched Palladiotype in 1917.

The commercial arc closed quickly. The Platinotype Company listed fifteen kinds of paper in 1911; commercial manufacture ended in the United States in the 1930s and in Great Britain in 1941. What revived the process was not a paper but a kit — chemicals sold for hand-coating — which is how almost every platinum print since has been made, and which is why the hazard that used to belong to a factory now belongs to whoever opens the bottle.

Recap

The metal in one 8 × 10 palladium print is about 40 mg by rod coating and about 60 mg by brush, and that figure is fully derivable from a published molarity and a published coating volume, with Ware’s own stated coating weights agreeing independently. The price is the one term the course cannot supply, and this page names it as the most consequential gap in the price file.

The permanence claim is four claims. The image substance really is inert; the surviving-prints evidence is real but drawn from a flattering population; the paper is what fails, and it fails because the process leaves it acidic; and the residual iron you did not remove on the evening you made the print is the variable you control. Accelerated ageing shows prints that looked acceptable on the day staining later in proportion to the iron left in them, and prints cleared by the sequence this part teaches showing no stain at all.

Palladium is chosen first for safety, then for chemistry, then for price. The palladium-toned kallitype is a legitimate route to the craft at a fraction of the cost and is not established as an equal in permanence. And the sentence a photographer may honestly write on the back of a print names the metal, the clearing and the paper — never a number of years, and never the word “archival”.

Check your understanding

Question 1. You coat a 16 × 20 inch print by glass rod at Ware's average specific coating volume of 25 cm³/m². Roughly how much palladium have you applied, and what is the largest assumption in your answer?

• About 40 mg, and the assumption is that the whole of it is reduced
• About 150 mg, and the assumption is that your paper takes sensitiser at the same rate as Ware's — the specific coating volume is a property of the paper, and his range across papers runs from 24 to 36 cm³/m²
• About 640 mg, because coating volume scales with the square of the linear dimension
• It cannot be estimated without knowing the price of the salt

Show the answer and why

Answer: About 150 mg, and the assumption is that your paper takes sensitiser at the same rate as Ware's — the specific coating volume is a property of the paper, and his range across papers runs from 24 to 36 cm³/m²

A 16 × 20 in coated area is about 0.22 m², four times an 8 × 10's; at 25 cm³/m² that is about 5.5 mL of mixed sensitiser, which at 0.25 mmol/mL is 1.4 mmol, or about 150 mg of palladium. Option three doubles the scaling incorrectly — area already scales as the square, and the volume scales with area. Option one is the metal on a sheet a quarter the size. And the assumption that matters is the paper: a thirstier sheet at 36 cm³/m² would take about 44 per cent more metal for the same picture, which is a real difference in a real budget.

Question 2. Which sentence may a photographer honestly write on the back of a palladium print they made?

• "Archival palladium print, expected life 500 years."
• "Platinum prints are the most permanent photographic objects known."
• "The image substance is metallic palladium, chemically inert under normal storage and display; the print was cleared in three baths and the masked margin showed no yellow under a bluish light."
• "Processed to archival standards using conservation-grade materials."

Show the answer and why

Answer: "The image substance is metallic palladium, chemically inert under normal storage and display; the print was cleared in three baths and the masked margin showed no yellow under a bluish light."

The acceptable sentence names the object correctly, states what was done, and reports a check that was actually made — one published claim and one measured one, both about this print. Options one and four both use "archival", which IPI warn is a marketing term that is neither standardised nor legal, and option one attaches a lifetime nobody has established for any photographic object. Option two is a claim about a different metal, and quite possibly about the wrong one: Ware's X-ray fluorescence work shows a 1:1 sensitiser depositing far more palladium than platinum.

Question 3. A student cannot afford palladium. On the course's own reasoning, what does the palladium-toned kallitype give them and what does it not?

• It gives an identical object at a tenth of the cost; nothing is lost
• It gives the surface, the scale, the craft and a real noble metal on the image at a small fraction of the metal — a whole litre of toner uses less palladium than one coated sheet — but the image is silver plated with palladium rather than palladium, and no source read establishes that the two are comparable in permanence
• It gives nothing useful, since the image is silver and will tarnish like any silver print
• It is more permanent than a palladium print, because two metals protect better than one

Show the answer and why

Answer: It gives the surface, the scale, the craft and a real noble metal on the image at a small fraction of the metal — a whole litre of toner uses less palladium than one coated sheet — but the image is silver plated with palladium rather than palladium, and no source read establishes that the two are comparable in permanence

The arithmetic is the striking part: Bostick and Sullivan build the toner from 7 to 15 drops of palladium solution per litre and state that 10 mL of that solution is 255 drops, so a litre of toner holds about 0.3 to 0.6 mL — less than one coated sheet uses. Option three is too harsh: toning a nanoparticulate silver image with a noble metal is a genuine permanence treatment and the mechanism is on record. Option four invents a claim nobody has made. What the course will not do is call the two equal in permanence, because no study read compares them.

Question 4. The Clarke and Hemmenway accelerated-ageing study is the strongest permanence evidence in this part. What is its most important finding for a printer?

• That platinum prints age better than palladium prints, so palladium should be avoided
• That prints with raised residual iron showed little or no visible stain on the day and would have been judged acceptable, then stained on ageing in proportion to the iron — so the clearing decision is invisible at the time it is made
• That accelerated ageing at 70 °C is not representative of real storage
• That gelatin-sized papers should never be used for any siderotype

Show the answer and why

Answer: That prints with raised residual iron showed little or no visible stain on the day and would have been judged acceptable, then stained on ageing in proportion to the iron — so the clearing decision is invisible at the time it is made

The finding that changes behaviour is the invisibility. A printer who judges clearing by looking at the print on the evening it is made is using a test the study showed does not work, which is why this part specifies a masked margin as a comparison and a three-bath sequence rather than a judgement. Option one over-reads a real detail — the effect was worse for palladium — into a recommendation the same study does not support, since the stain occurred with ferric oxalate and no noble metal at all. Option four similarly over-reads: gelatin sizing retained more iron, which is a reason to prefer alum-rosin sizing and to clear longer, not a prohibition, and Ware says gelatin has no adverse effect on pure palladium prints.

Question 5. Why is the mounting rule for a palladium print different from the one Part XXI gives for a cyanotype?

• It is not different; both must be mounted on unbuffered board
• A cyanotype's image substance is destroyed by alkali, so a buffered mount attacks the picture; a palladium image is indifferent to alkali and the acidity is in its own paper, so the conservation recommendation is a neutral pH board protecting a paper object rather than an image
• A palladium print must be mounted on a buffered board, to neutralise the acid the process left in it
• Palladium prints should not be mounted at all

Show the answer and why

Answer: A cyanotype's image substance is destroyed by alkali, so a buffered mount attacks the picture; a palladium image is indifferent to alkali and the acidity is in its own paper, so the conservation recommendation is a neutral pH board protecting a paper object rather than an image

The two rules come from opposite chemistry. Prussian blue is decolourised irreversibly by alkali, and Ware's arithmetic on ISO 9706 puts a permanent paper's reserve at an eightfold molar excess over the iron in a siderotype coating — so for cyanotype the buffer is an attack on the image. Palladium metal is indifferent to it. Option three is the tempting inference and the course does not make it: it is chemically reasonable, the AIC nonetheless specifies neutral pH board, and where a conservation body's recommendation and a plausible inference disagree, the course follows the conservators and says so.

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