Running a platinum or palladium session

Purpose

To coat, expose, develop and clear a platinum-group print without weighing a noble-metal salt, without wasting a drop of the course’s most expensive solution, and with a margin left that proves the clearing worked.

When to use it

A coating day and a printing day, which may be the same day. After exposure the sheet is never stock: it is developed immediately.

Weighing a platinum or palladium salt as a powder is excluded from this course’s sessions. The platinum salt carries a respiratory-sensitisation statement and the tightest exposure limit in the course, and preventing that exposure means a fume cupboard, controlled waste and health surveillance. This procedure uses bought solutions, palladium included.

Before you start

You should already know why the iron and metal volumes are equal and what an alkaline buffer in the paper does, from the coating lab.

Level B. Nitrile gloves from the first bottle to the last rinse, changed if solution gets inside one; sealed splash goggles, the metal salt’s eye statement being damage rather than irritation; an apron; tongs dedicated to this bench and never shared with a silver one, because oxalate and silver must not meet.

One raised step, declared here: warming the developer, to no more than 38 °C. Its controls belong before the step — the tray is warmed by standing it in a larger tray of hot water, never on a hotplate and never over a flame; the hot-water tray is filled first; the bath is carried at half depth at most, with gloves, goggles and an apron. Above that ceiling the course has no sourced scald control.

A ventilated room and a covered tray between prints. No source read gives an airborne figure for these baths; the corpus carries one printer’s report of headaches from a reused developer. Believe yourself over this paragraph if you develop one.

And the ferricyanide bottle from the sensitiser quality test stays out of the room, because today’s bench has acid on it. The acid exclusion rule governs it.

Procedure

Coating day

1. Write down both bottles’ actual strengths; where one is not published, write not published rather than a guess. A drop count for one supplier’s bottle is not a drop count for another’s.
2. Calibrate your dropper today: fifty drops of distilled water into a tared beaker, read, divide, repeat three times, report the mean with its spread.
3. Test the iron solution at the separate hexacyanoferrate station, with its own tube and waste: read both the darkness in the tube and the photoactivity beside a lamp.
4. Stand the noble-metal waste container out, labelled, before anything is opened.
5. Read the hygrometer at the bench and in the drying enclosure. Below the process’s stated humidity floor, put a tray of water in the box, wait an hour and read again rather than coating.
6. Rehearse with plain water or a cheap sensitiser until two consecutive sheets look even.
7. Tape, level and mark the sheet by the coating procedure; only then mix.
8. Draw equal volumes of iron and metal solution with their own syringes, expel both into the mixing glass, and mix by drawing the liquid gently in and out of the delivery syringe.
9. Coat one sheet’s worth and no more: a mixture you do not coat is metal thrown away.
10. Dry the sheet in still air, in the dark, and leave it there.

Printing day

11. Mix the developer ahead, to the published strength, neutral or only just acid.
12. Mix the three clearing baths with tap water at room temperature: acidic chelator first, sulphite made fresh today, alkaline chelator last.
13. Mask the borders with Rubylith or black polythene: that margin is the only visual test of complete clearing you will have.
14. Back the sheet with a gas-permeable felt blanket, not a plastic sheet, so the photolysis’s carbon dioxide can leave.
15. Run the ultraviolet unit up about five minutes, then expose a test strip in third-of-a-stop steps and take it through the whole sequence before judging.
16. Expose the print at the strip’s dose.
17. Have the developer in its tray at a measured temperature before the frame is opened.
18. Pour, do not lower. Cover the whole surface in one movement, fast enough to break any bubbles, then agitate a minute or two and drain.
19. Clear through bath 1, bath 2 and bath 3, with a half-minute rinse between each.
20. Inspect before you wash. Under a bluish light, compare the masked margin with the uncoated paper beside it. Any yellow is residual iron: prolong bath 3 and look again.
21. Wash thirty to sixty minutes in running water, or in at least three fresh static baths.
22. Drain face out on a near-vertical sheet for ten minutes, then dry flat at room temperature on a fibreglass or plastic screen.
23. Route the waste by the segregation sheet: developer, clearing baths 1 and 3 and any toner to the noble-metal container for recovery; the sulphite discarded; the wash collected. Check your local regulations, which govern the route and which the disposal caveat explains the course cannot give you.

How you know it worked

• No noble-metal salt was weighed, and every solution came from a bought bottle whose strength is recorded.
• The dropper was calibrated today and the volume mixed was for one sheet.
• The developer covered the whole sheet in one movement and the image arrived evenly.
• The masked margin is as white as the uncoated paper beside it, read before the wash.
• The sulphite bath was made today, and the acidic chelating bath came first.
• The hexacyanoferrate bottle never entered the room.

If a step fails

Step 2, the kit’s drop count and your own dropper disagree by a quarter. Yours governs; two suppliers of the same process publish drop volumes that far apart.

Step 3, the tube goes deep blue at once. The iron has partly reduced itself and will print weak and foggy. Replace it rather than compensate by exposure.

Step 5, the room is far below the humidity floor. Do not coat: tonal reversal appears in the tray after the metal has been spent.

Step 8, one syringe was used in both bottles. Both are suspect. Record the crossing and expect fog or a patchy image rather than blaming the exposure afterwards.

Step 17, the sheet was not completely dry before exposure. That is the published cause of a splotchy appearance in the developer. Dry the next one fully rather than developing longer.

Step 18, the image comes up a second late along one edge. A lap mark from the pour rather than a chemistry fault. Practise the pour on a rehearsal sheet.

Step 20, the margin is still yellow after a prolonged bath 3. Record it and finish the print: a note that clearing was incomplete beats a fourth bath invented at the bench.

What to record

Both bottles’ strengths and lots; your drop volume with its spread; the iron test result; the paper and its lot; temperature and humidity at coating and drying; the volume coated and the area, as cubic centimetres per square metre; the strip’s exposure and the dose given; the developer’s strength and temperature and whether the raised step was taken; each clearing bath’s strength, time and print count; the margin reading before the wash; and where each stream went.