Assignment 1: A Botanical Cyanotype Photogram, After Atkins

In October 1843 Anna Atkins posted the first part of Photographs of British Algae to a dozen or so botanical friends. Every plate in it was made the way you are about to work: a dried, pressed specimen laid on a sheet of coated paper, left in the sun, rinsed in water, hung up to dry. She did it about five thousand times. You are asked for three.

The intention

Make three finished botanical photograms that you would be willing to show someone, and be able to say why each one is arranged the way it is.

That is the whole brief, and the two halves are equally weighted. This is the course’s first assignment, the first piece of the assignment path, and the first picture you make that does not destroy itself: the unfixed silver photogram is the control against which this one is read. Keep all three prints; they go into the Level 1 portfolio.

Three things you are not doing. You are not mixing chemistry: the paper arrives coated, and Part XXI owns the sensitiser, the coating and the variants. You are not using a camera. And you are not being asked for a beautiful print — you are being asked for a print whose faults you can name, which is a harder and more useful thing at this stage.

Learning objectives

By the end you should be able to:

• run an exposure series and choose a working exposure from it, rather than guessing and hoping;
• explain, in two sentences, why this print is permanent and the silver photogram is not;
• keep the course’s exposure log well enough that a stranger could repeat your best sheet;
• describe your own picture in the vocabulary of placement, edge and tonal range, and say what you would change next time;
• state what is on the paper you are handling, what its hazards are, and which control addresses each.

Prerequisites

Herschel: hypo, Prussian blue and the words of photography is assumed: the two-step iron chemistry in outline, why water is enough, and why Prussian blue must be kept away from alkali. The unfixed silver photogram should be at least a few days into its seven-day log before you start, because the comparison is the point.

No darkroom, no camera, no chemistry and no UV lamp. Sunlight is the only source of ultraviolet anywhere in Part I; the course builds an exposure unit in Part XVI, inside an enclosure, with its own hazard assessment.

Safety classification

Level A. The criteria of the classification rubric that decided it:

• Substances and quantities. Nothing is weighed, dissolved, diluted or poured. The only chemistry present is a dried coating on a purchased sheet, and it leaves that sheet only into the rinse water.
• Energy. No flame, no heater, no lamp, no mains. The only energy source is sunlight, outdoors, which is a real hazard and is controlled below.
• Waste. A few litres of rinse water carrying a small quantity of iron salts, and dry offcuts. Handled under Disposal considerations.
• Incompatibilities. One, and it is absolute: nothing acidic, nothing containing bleach, and no heat source comes near the paper or its rinse water.

What is not a hazard here, and why. There is no inhalation route, because nothing on this page is a powder, a vapour or a spray: the salts arrived dissolved, were dried into paper fibres by the manufacturer, and stay there until water lifts them. There is no splash hazard from a concentrated solution, because the most concentrated liquid you will handle is a tray of tap water with a faint yellow tinge in it. There is no fire risk and no electrical risk. And the hydrogen cyanide that worries people about the word ferricyanide is not released here: the cyanide in potassium ferricyanide is bound to iron in a complex anion, and Ware’s assessment of the traditional process is that a normal exposure and wash will not give off any significant or perceptible amount of it. The incompatibility below is stated because that assessment applies to this procedure, and a reader who improvises with lemon juice or household bleach has left it.

Say the same sentence about the substances loose in a bottle and it stops being true, which is the point of assessing procedures rather than chemicals. Part XXI mixes these salts as powders, and its page carries a different assessment.

Hazards

Solar ultraviolet, on skin and eyes. The exposures happen outdoors, in the strongest sun you can find, and the exposure series means standing there watching. ICNIRP’s guidance for outdoor workers gives the points that matter: the four hours around solar noon carry the greatest risk; sunburn happens under cloud as well as under clear sky, and breaks in cloud can push the ultraviolet level to or above the clear-sky value; and if your shadow is shorter than you are, the ultraviolet is strong. Do not look at the sun at any point; nothing here requires it.

The dried coating, on skin and in eyes. Handling coated paper with dry hands transfers very little, but dust from a cut edge and a rubbed eye is a plausible route. PubChem’s aggregated ECHA classification for potassium ferricyanide carries the signal word Warning, with causes serious eye irritation on 62.8 % of notifications, harmful if swallowed on 25.3 %, and causes skin irritation on 10.5 %; ferric ammonium citrate carries causes skin irritation and causes serious eye irritation on about 90 % of notifications each. Wash your hands when you finish handling paper and before you eat. Do not eat or drink at the working surface. Keep the paper and the tray out of reach of children and animals. Expect blue stains on hands and clothing: they are cosmetic, and they are also the reason to work in an old shirt.

Acids, bleach and heat, near the paper or the rinse water. Ware’s hazard list states that potassium ferricyanide “is incompatible with concentrated acids, which may release deadly hydrogen cyanide gas.” Nothing in this assignment needs an acid or an oxidiser, so the control is simply that none is present: no citric acid, no lemon juice, no vinegar, no hydrogen peroxide, no household bleach, no drain cleaner, and no rinse water poured into a sink that has bleach standing in it. Some published cyanotype instructions do use dilute citric acid or 3 % hydrogen peroxide to speed up the final blue; both are omitted here, and Part XXI will make its own ruling on them with its own hazard assessment.

Cuts. Trimming paper and mounting card means scissors or a craft knife. HSE’s general principles transfer: keep the blade sharp, cut on a stable surface, never try to catch a falling blade, retract or sheath it the moment you put it down.

Glass. A sheet of picture glass holds the specimens flat. Tape all four edges before you start, carry it flat, never lean it against anything.

Plant material. This assessment covers the paper, the glass and the sun. It does not cover whatever you pick, because the course has not assessed the flora of your area and cannot. Use plants you can name; keep sap off your skin; wash your hands after handling and pressing them; and if you do not recognise a plant, do not use it. Where a species is known locally to be irritant, that local guidance governs, not this page.

Required PPE

The protection here is sun protection and hand hygiene, not chemical protection against a concentrated solution.

• A wide-brimmed hat and ultraviolet-blocking sunglasses. ICNIRP gives the ocular exposure ratio as about 0.5 for sunglasses alone and about 0.02 for sunglasses with a brimmed hat, so the pair is worth far more than either.
• Long sleeves; ICNIRP records that most summer clothing gives a protection factor above 10. Sunscreen on what is left uncovered, reapplied, and shade between exposures.
• Disposable nitrile gloves for the wash, if you would rather not stain your hands. They are a convenience and a stain control rather than a barrier against a corrosive, and dry hands are what the paper needs — the manufacturer’s own instructions warn that damp hands leave water spots on a sensitised sheet, and the Library of Congress’s handling guidance for photographs is freshly washed hands, held by the edges, off the image surface.
• An apron or an old shirt. Prussian blue on cotton is very difficult to remove, which after all is the point of the process.

Ventilation

Ventilation is not one of the controls on this page, because nothing here produces a vapour, a mist, a dust or an aerosol: the coating is dry and bound in paper, and the wash is water at room temperature. You will be outdoors for the exposures because that is where the ultraviolet is, and at a sink or a table indoors for the wash.

Materials

Item	Quantity	Notes
Pre-coated cyanotype paper	6 to 8 sheets, A5 or larger	See the note below on choosing it. One sheet becomes the test strip; three become the finished prints; the rest are spares.
Plant specimens, pressed and dried	a good handful	Flat or flattenable: ferns, grasses, cow parsley, seed heads, skeletal leaves, single flowers. Gather more than you think you need, and press them days in advance.
Newspaper and a heavy book, or a flower press	—	For pressing the specimens flat and dry.
Picture-frame glass or a clip frame	1, larger than the paper	Edges taped. A clip frame is ideal because it holds pressure evenly.
Rigid board	1, larger than the glass	Hardboard or thick mounting card.
Opaque card	2 sheets	One to carry the sandwich face-down, one cut into the sliding mask.
Shallow plastic tray or basin	1, larger than the paper	Kept for this work and nothing else; never a container also used for food.
Drying line and pegs, or a plastic mesh rack	—	Prints dry face up, out of direct sun.
Masking tape, pencil, timer	—	Pencil, not pen.

!Choosing the paper, and what to check before you buy

The course verified the composition and working instructions of one make in detail: Jacquard’s pre-sensitised cyanotype cotton sateen sheets, whose maker publishes both the sensitiser formula (ferric ammonium citrate with potassium ferricyanide, mixed one to one) and the processing instructions, and puts a sunlight exposure at generally three to ten minutes, depending on conditions. That is a fabric rather than a paper. Pre-coated cyanotype paper is widely sold — the Getty atlas notes that sensitised cyanotype paper is still made for student instruction — but the course could not verify a second product’s stated composition from its maker’s own documentation, and will not recommend by brand on that basis.

So here is the test to apply yourself, which is a more useful thing to own than a brand name:

1. Does the maker name the chemistry? You want ferric ammonium citrate (also sold as ammonium iron(III) citrate) and potassium ferricyanide. If the packaging names neither, ask.
2. Does it wash in plain water? A genuine cyanotype needs nothing else. If the instructions call for an ammonia vapour box, a developer, or a bath of anything but water, it is not this process.
3. Is it blue before you wash it? A cyanotype coating is yellow-green and turns bronze or grey-blue under long exposure; the strong blue arrives in the water. A paper that is already brilliant blue in the packet is something else.

The one to avoid is the family of diazo “sun print” products. Diazo is a different chemistry entirely, and it is the chemistry that replaced the blueprint: the Getty atlas dates the changeover to about the 1950s. Diazo papers are also blue, which is exactly why they get confused with cyanotypes. Some craft “sun print” kits are genuine cyanotype; some are diazo; some are dye-based systems, like the maker’s own SolarFast, which is described as a true dye that bonds to the fibre rather than a pigment precipitated inside it. Read the instructions before you read the marketing.

Storage. The manufacturer gives sensitised paper a working life of about six months, stored cool, dry and sealed in the dark to avoid oxidation, and notes that coated paper may darken over time without necessarily being spoiled — test it rather than throwing it away. Buy what you will use.

Chemicals

None is mixed, diluted, weighed or poured. There is no chemical inventory to keep for this page. For completeness, this is what is present on the sheet, where it is, and what happens to it:

Substance	Where it is	Handled as a substance?	What becomes of it
Ferric ammonium citrate (CAS 1185-57-5)	Dried into the paper fibres, part of the coating	No	The light-struck part is reduced and consumed; the rest washes out
Potassium ferricyanide (CAS 13746-66-2)	Dried into the paper fibres, part of the coating	No	Reacts where iron(II) was formed; the rest washes out
Prussian blue	Formed in the fibres during exposure and washing	No	Stays: it is the picture
Water	The wash	Yes, in the ordinary sense	Carries the unused salts to waste

The proportions on your sheet are the manufacturer’s and are not printed on the packet. Its published sensitiser for coating your own is about 20 % w/v ferric ammonium citrate mixed in equal volumes with about 9 to 10 % w/v potassium ferricyanide — the two figures differ slightly between the maker’s own FAQ and its detailed instructions, which is itself worth noticing — and that is close to the classic formulation Ware traces back to Herschel’s 1842 paper. Do not treat those numbers as the composition of your sheet. They are the right order of magnitude and nothing more.

Equipment

Scissors or a craft knife and a cutting mat; a steel rule; a timer or a phone clock readable in sunlight; a notebook and a pencil; a flat outdoor surface — a paving slab, a garden table, a windowsill wide enough for the board; a sink or an outside tap; and a dim indoor space to load and unload the frame. A curtained room with one lamp well away from the work is enough. Cyanotype paper is not sensitive to tungsten light in the way silver paper is, but every minute in room light spends a little of the coating.

Estimated cost

Cost band £: a pack of pre-coated paper, a piece of glass you may already own, a plastic tray. Nothing here is consumed except paper. Dated price ranges live in the laboratory planner rather than in the lesson text.

Waste streams

Two, both small.

Rinse water, a few litres, carrying dissolved ferric ammonium citrate and potassium ferricyanide that light did not use, plus a little loose Prussian blue pigment. It will be distinctly yellow at first and should run clear by the end.

Dry solid: offcuts, spoiled sheets and the sheet you cut into a test strip, all carrying a small quantity of the same salts in paper. Keep them dry and separate from your finished work.

See Disposal considerations, and note the one rule that governs both: neither stream meets an acid or a bleach.

Preparation

1. Press the specimens, days in advance. Lay them between sheets of newspaper under a heavy book, or in a flower press, for three days or more. Flat matters more than beautiful: a specimen that stands 2 mm off the paper throws a soft penumbra instead of a sharp edge. Ware notes that Atkins’ plates were printed directly from dried, pressed algae, usually unsupported, and that is why they are so sharp.
2. Dry them properly. The manufacturer’s instructions are explicit that the paper and everything touching it must be dry, and its troubleshooting list attributes blotches to moisture — including moisture that leaves the specimen during a long exposure. A pressed fern is dry; a fresh one is not.
3. Rule up the log before you go outside. The tables under The record to keep are the assignment as much as the prints are.
4. Tape the glass edges on all four sides and check the board is flat and clean.
5. Cut the mask. A piece of opaque card slightly larger than a sheet, marked into six equal bands.
6. Work out the day. Direct sun makes this quick and the differences legible; bright overcast works and takes longer. Check the ultraviolet index forecast, and read Hazards again if you are going out around the middle of the day.

The contact stack, bottom to top

1. 1Rigid board — flat, larger than the glass; carry the whole stack by this
2. 2Coated paper, coated side up — the even yellow-green face
3. 3Pressed specimens — flat against the paper; a 2 mm gap costs you the edge
4. 4Taped picture glass — weight and pressure; tape all four edges before you start
5. 5Opaque card — on until the timer starts, back on when it stops

Contact and pressure decide sharpness in a photogram, and they are the only two variables you control after the exposure time. A clip frame does the job better than loose glass because it presses evenly.

The making

Stage 1: the test strip

Do this first, every time, on every new day. The answer changes with the season, the hour, the sky and the packet.

1. Cut one sheet into a strip and build the stack with one small flat specimen on it — a single grass head is ideal, because it has both an opaque stem and a translucent tip.
2. Lay the marked mask over the glass so that all six bands are covered, carry the board out face down, and note the time, the date, the sky and whether your shadow is shorter or longer than you are.
3. Lift the mask clear, start the timer, and slide it back one band at the cumulative times 16, 8, 4, 2, 1 minutes and 30 seconds, so that band 1 gets the whole sixteen minutes and band 6 the last thirty seconds only. Re-cover, carry in.
4. Wash the strip as in Stage 3, dry it, and only then choose your working exposure. A cyanotype cannot be judged wet or unwashed.

=Why that bracket, and what it is not

It is an estimate, and it is argued rather than measured. Three independent figures bracket it. The manufacturer’s product page puts a sunlight exposure at generally three to ten minutes for its pre-sensitised sheets, and its comparison sheet gives 3 to 15 minutes; its detailed coating instructions widen that to 1 to 30 minutes. And Ware calculates the answer from first principles: a proto-photographic process needs a radiant exposure of about 34 J/m² for a just-perceptible image and seven to eight stops more for full density, and average sunlight delivers roughly 30 to 40 W/m² of ultraviolet A, which puts full darkening “in the order of 2 to 4 minutes … in agreement with all experience.”

So a sixteen-minute bracket comfortably contains the answer for direct summer sun, and it is the wrong bracket for a British February. If every band on your strip looks the same, move the whole bracket by a factor of four in the indicated direction and repeat. The course has not published its own measured series for this page; your strip is the measurement.

Stage 2: the three prints

5. Compose on a spare sheet of plain paper first, so that you are moving specimens around without spending coating. The composition notes below are the substance of this stage.
6. Build the stack in dim light, coated side up, and get the specimens into real contact with the paper.
7. Expose for the time your strip gave you. Watch the coating rather than the clock: the exposed ground goes from yellow-green through grey-blue to a dull bronze, and the manufacturer’s instruction is that over-exposure is almost always preferable to under-exposure, with the fully exposed sheet looking bronze. Ware describes the same thing as the shadows reversing and the highlights going distinctly green, and says the exposure is right when the image looks blocked up.
8. Re-cover, carry in, wash immediately.

✕The reversal is not a mistake

The first time you take out a sheet that has gone bronze and looks worse than it did five minutes earlier, the instinct is to conclude you have ruined it. You have not. Ware’s account of the classic process: the uncovered sensitiser first darkens to blue and then reverses back to a pale blue-grey, and that “solarised” look is the sign of a correct exposure, because the reversal lets more light in and builds more product where the deepest tone will be. It reads as a fault and behaves as the opposite. Judge after washing and drying, and only then.

Stage 3: the wash

9. Fill the tray with cool water and slide each print in face down, in one movement, without splashing; the manufacturer’s troubleshooting list traces blotches to drips and splashes before immersion.
10. Wash for at least five minutes with gentle agitation, changing the water every couple of minutes, until the yellow has gone from the areas your specimens covered and the water runs clear. Ware allows up to twenty minutes for a fully cleared highlight and warns that the extended washing which fully clears the paper also leaches out blue pigment and truncates the light tones. You are choosing between a clean white and a strong high tone; note in the log which you chose.
11. No soap, no detergent, no washing soda. The wash is water. Anything alkaline attacks the picture itself, for the reason the Herschel page gives.
12. Lift by a corner, let it drain, and dry face up on a rack or a line, out of direct sunlight. The manufacturer’s own instruction is not to dry in direct sun.

What each step does

1. 1ExposeLight reduces iron(III) to iron(II) wherever the specimen did not block it.
2. 2WashIron(II) meets ferricyanide and becomes insoluble Prussian blue; everything unused dissolves and leaves.
3. 3DryAir oxidises colourless Prussian white back to Prussian blue, so the print deepens for hours after it looks finished.
4. 4KeepNothing photosensitive is left in the paper. This one does not need Part XI.

Four steps, one of which is doing nothing. The chemistry behind them is on the Herschel page and in full in Part XXI.

Expected observations

Marked, as everywhere in this course, by whether a source stands behind them.

• The coating is yellow-green and turns bronze. (Sourced: the manufacturer states that the fabric looks bronze once fully exposed; Ware describes the same reversal to a pale blue-grey with distinctly green highlights.)
• Almost nothing looks like a picture until the print hits the water, and then it does, at once. (Sourced: the manufacturer states that the reaction “won’t reveal itself … until you put the fabric in water. Then it will instantly turn blue.”)
• A yellow stain lifts off into the first change of water. (Sourced: Ware’s instruction is to wash until the yellow sensitiser has entirely gone from the highlights, and the manufacturer’s is to change the water until it runs clear.) That yellow is the unreacted sensitiser leaving. When it stops appearing, the wash is nearly done.
• The dried print is markedly deeper than the wet one, and goes on deepening for some hours. (Sourced: Ware attributes it to aerial oxidation of Prussian white to Prussian blue over several hours of drying.)
• A working exposure in direct summer sun somewhere between two and ten minutes. (Prediction, bracketed by the manufacturer’s 3-15 minutes and Ware’s calculated 2-4 minutes for full density. Your strip is the measurement; write it down.)
• A translucent specimen prints as a mid-tone, an opaque one as paper white. (Prediction, from the geometry of contact printing. It is the one thing that makes a photogram more than a silhouette, and it is why fern and grass are better subjects than a coin.)
• An extra sheet of glass over the frame slows it, but not by much. (Prediction. Ordinary window glass transmits some radiation down to about 310 nm, so most of the UVA the process uses gets through; ICNIRP records the transmission. Measure it: two identical strips, one under an extra sheet of glass, same exposure.)

Composition, after Atkins

Three things worth stealing from British Algae, and one worth arguing with.

She let the specimen decide the format. A plate of Atkins’ is usually one organism, placed to fill the sheet on its own terms — a frond that sprawls gets room to sprawl, a compact one is set high with air beneath it. Nothing is cropped to fit a rectangle it did not want.

The edge is the picture. In a photogram, everything you have is outline and translucency. A specimen laid so that a tip runs off the sheet gives you a picture with no edge to it; one laid a centimetre inside gives you a shape. Decide which you are doing.

The label is part of the image. Atkins wrote each Latin name on a translucent slip and printed it with the specimen, so it appears in white on the blue like everything else. Try it on at least one of your three: write the plant’s name, in pencil or ink, on tracing paper or thin baking parchment, and lay it on the sheet with the specimen. It changes the object from a picture of a plant into a record of one.

And the thing to argue with. Atkins was making a taxonomic reference, and her arrangements are regular because regularity serves comparison. You are not making a reference. If you find yourself centring every specimen because that is what the plates do, you have copied the constraint and missed the decision.

🕰What she was actually solving

Atkins’ preface says it plainly: “The difficulty of making accurate drawings of objects as minute as many of the Algae and Confervae, has induced me to avail myself of Sir John Herschel’s beautiful process of Cyanotype, to obtain impressions of the plants themselves.” A drawing of a seaweed is an interpretation; a contact print of one is a measurement, at 1:1, of an object that was physically present. That is the argument for photography as evidence, made in 1843 by someone with a specific scientific problem — and it is worth noticing that the reason it worked is the same reason your prints will be sharp: a pressed alga is flat, and flat things print perfectly.

The record to keep

This is the course’s first exposure log, and it is graded. Camera fields do not apply and are left out.

Table 1. Exposure series. One row per band.

Band	Cumulative exposure	Sky and time of day	UV index (if known)	Tone after washing and drying, 0 to 5	Fine detail still readable?
1	16 min
2	8 min
3	4 min
4	2 min
5	1 min
6	30 s

Chosen working exposure, and why: one sentence, naming the band and the trade-off you made.

Table 2. The three prints.

Print	Date	Start time	Sky	Exposure	Wash time and changes	Specimens	Notes
1
2
3

Table 3. The comparison. Fill this in on the same day you complete day 7 of the silver photogram.

Property	Unfixed silver photogram	Cyanotype photogram
Image substance
What was still light-sensitive when you finished
What the processing step removed
Condition after seven days in room light

📓Lab notebook

Record the sky in words you will still understand in a year — “clear, no cloud”, “thin high cloud, sun visible”, “broken cloud, sun in and out”, “overcast, sun not visible” — and record the ultraviolet index if your weather service gives one. Both are cruder than a light meter and both are repeatable, which is the property that matters. A photogram made at 13:00 in June and one made at 13:00 in October are not the same experiment, and the log is the only thing that will tell you so afterwards.

The critique

Write it before you show anyone. Six sentences, one per heading, on each of the three prints.

1. Intent. What is this picture of, and what did you want a viewer to notice first?
2. Placement. Where does the specimen sit in the frame, and what did that decision cost or buy?
3. Edge. Is the outline crisp, and where it is not, is that a contact failure or the specimen’s own translucency? These look similar and are not.
4. Tonal range. Do you have both paper white and full blue in the same sheet? If the whites are pale blue you under-washed or over-exposed; if there is no deep blue you under-exposed.
5. The accident. Name one thing you did not intend. Keep or reject it, and say which.
6. Next time. One change, stated as an action, not as an aspiration. “Press the fern for a week” is a change; “compose better” is not.

Then answer the assignment’s chemistry question in two sentences: why is this print permanent when the silver photogram is not? The answer is on the Herschel page and you should be able to give it without looking.

Troubleshooting

What you see	Most likely cause	What to do
The whole print is pale and washed-out	Under-exposure, or over-washing	These are distinguishable. Under-exposure leaves both the ground and the highlights weak; over-washing leaves a good deep ground and empty, chalky high tones, because the extended wash leaches the light blues first. Compare against your test strip, then change one thing.
The blue is there but the shapes are soft and doubled	The specimen was not in contact	Weight the glass, or use a clip frame. A thick stem lifts everything around it; press harder or press flatter.
Blotches and comet-shaped marks	Moisture: damp hands, a damp specimen, a splash before immersion	The maker’s instructions name all three. Dry hands, dry specimens, and slide the print in swiftly and without splashing.
The paper was already blue-grey in the packet	Fogged in storage: light, damp or age	Test a strip with a coin on it for five minutes. The maker notes that darkened paper is not necessarily spoiled and may just need a longer, warmer rinse.
Uneven blue in broad flat areas	Uneven pressure, or uneven coating	Rotate the board halfway through a long exposure and see whether the pattern moves. If it does, it is your light; if it does not, it is the sheet.
The print faded after a few weeks on a wall	Light-fading of Prussian blue	Put it in the dark for a fortnight and look again. Ware records that the light-fading is reductive and reverses in air; a print that recovers in a drawer has told you it is fading rather than degrading. Then hang it somewhere else.
The print yellowed or the blue went patchy after mounting	Alkali	Prussian blue is destroyed by alkali; the manufacturer warns against phosphates and high pH, and Ware reports that a pH 9.4 buffer decolourises it in one to ten minutes. Boards sold as archival are buffered with calcium carbonate, whose saturated solution sits at that very pH. Use unbuffered mounts and folders for cyanotypes.
A fabric print faded in the wash	Detergent	Cold water and a non-phosphate detergent, as the manufacturer specifies, and keep washing to a minimum.

Clean-up

Empty the tray, rinse it and put it away with the rest of your dedicated equipment. Untape the glass and store it flat. Sweep up offcuts and keep them dry. Wash your hands — this time because of what you were handling, not only because of what the paper needs.

Storage

Prints dry flat under a clean weight overnight, then live in an unbuffered folder or interleaved with plain paper, out of daylight. Handle by the edges. Write the date and the exposure on the back in pencil, because in six months you will not remember which was which and the log entry is useless without the print it names.

Unused pre-coated paper goes back into its sealed, opaque bag, in a cool, dry, dark place, and is used within the manufacturer’s six months.

Disposal considerations

The rinse water. Ware’s assessment of cyanotype effluent is that the processing solutions are very dilute and that, dichromates aside — and no dichromate appears anywhere on this page — there is nothing in a cyanotype sensitiser or its processing baths that needs treating as chemical waste at these concentrations. He notes that ferric ammonium citrate is used medicinally as an iron tonic and as a food additive; that ferricyanide reduces in the environment to the more stable ferrocyanide, which is a permitted anti-caking agent in table salt; and that Prussian blue is very insoluble and is itself used medically as an antidote to thallium and caesium poisoning.

That is a chemist’s assessment of the substances, not a permission. Local regulation governs, and it differs between countries, regions and water companies — check your local regulations. In the United Kingdom, the government’s household hazardous waste service is a starting point, and it is worth noticing that the page itself covers England and Wales only, which is exactly why this course refuses to give a universal instruction. Where a household chemical collection exists, use it. Where your water goes to a septic tank, a reed bed or a soakaway rather than to a treatment works, treat that as a reason to ask before you pour anything, because the dilution argument assumes a sewer.

The one absolute. The rinse water never goes into a sink or a drain that has bleach or an acidic cleaner standing in it, and is never itself acidified. Run the tap first if you are unsure.

The solids. Dry offcuts and spoiled sheets are paper carrying a small quantity of iron salts. Keep them dry, keep them out of the compost, and put them into the same route your local authority gives for the rinse water rather than assuming they belong in the recycling.

What to submit

• Three finished prints, dried flat, dated and labelled in pencil on the back.
• The washed and dried test strip, with its six bands identifiable.
• The completed exposure log: Tables 1, 2 and 3, with the chosen working exposure and its one-sentence justification.
• The critique: six sentences on each print, plus the two-sentence chemistry answer.

Keep all of it. Part XXI asks you to make the same picture with a sensitiser you have mixed yourself, and this is the “before”.

Further work

• One extra sheet of glass. Two identical strips, same specimens, same start, one with a second sheet of window glass laid over the frame. Predict the ratio first from the ICNIRP transmission figure, then measure it.
• A hand-drawn transparency. Draw with a black marker on tracing paper or drafting film and print it as you would a negative. It is the cheapest way to understand what a negative has to do: wherever your ink is opaque to ultraviolet you get white, and wherever it is not, you do not. Test your pen on a strip before you commit a drawing to it.
• Fabric. The same process on pre-sensitised cotton. The manufacturer’s rules are cold water, a non-phosphate detergent and as little laundering as possible, and its own comparison sheet concedes that cyanotype on fabric is less wash-fast than its dye-based alternative. Worth knowing before you make a cushion.
• The seasonal series. Repeat the test strip on the first clear day of each month for a year, in the same place at the same hour, and keep the strips together. By next summer you will own a calibration nobody could have given you.
• The one to leave for Part XXI. Do not try to intensify a pale print with hydrogen peroxide, citric acid or lemon juice on the strength of an internet recipe. Peroxide reoxidation and acid clearing are both real published practices, both change the hazard assessment this page was written under, and Part XXI will rule on them with its own.