Dedicating tools to one process

Purpose

To make it physically impossible to carry one process’s chemistry into another’s sheet, by giving each process its own implements and marking them so a tired hand in dim light picks up the right one.

When to use it

Whenever two alternative processes share a room, a bench, a drying line or a cupboard — which is every home darkroom that reaches Part XXI and beyond. Set it up once, at the start of the cluster, and audit it whenever a new process joins.

The rule about acids at these benches is separate and stricter; it is on the acid exclusion sheet and this one does not restate it.

Before you start

You should already know why a brush that has carried ferricyanide into a platinum sensitiser has not made a variant but a defect that cannot be diagnosed from the print, from the negatives and papers lesson.

Level A as an organising procedure, sitting inside sessions whose own levels are higher. Nothing here is mixed or opened; what it does is lay a bench out. Where you are washing implements that carried a sensitiser, the session’s own gloves and eye protection stay on.

On the bench: waterproof labels or coloured tape in one colour per process; a rack or a hook per process rather than a jar of everything; and the labelling procedure for anything that holds liquid.

Procedure

Setting the scheme up

1. List the processes the room will run this season, and give each one a colour and a written name.
2. Buy or set aside one brush per process. A brush is the item that cannot be got genuinely clean, and it is the item every supplier warns about by name.
3. Reject any brush with a metal ferrule for silver work: silver nitrate reacts with the ferrule and prints the reaction as a stain. A brush bound with thread is the published alternative.
4. Give each process its own trays, and make them non-metal. No sheet iron, no exposed iron in a chipped enamel dish, no stainless steel at a silver bench.
5. Give each process its own tongs, its own funnel and its own waste container, and mark all four in that process’s colour.
6. Give each bottle its own syringe or pipette, and add one more for delivery. A syringe that has been in two bottles has mixed them.
7. Mark the glass rod as the one deliberate exception, and mark it as shared: it is rinsed under the tap the moment a coating is finished, before anything can crystallise on it, and it is the only implement that can be inspected and seen to be clean.
8. Hang or rack each set separately, and keep them off a common draining board.
9. Separate the room into a wet fabrication area and a dry printing area, and keep paper, boxes and negatives on the dry side.

Using it

10. Take out only the set for the process you are running, and put the others away before you start.
11. Rinse the rod immediately after each coating pass, and blot the residual bead at the foot of the coating with clean blotting paper before the sheet is moved: crystals formed there damage a negative.
12. Wash a brush thoroughly the moment it is finished with, in the process’s own water, and route that rinse to that process’s own labelled container. Check your local regulations, which govern where it goes next.
13. Change gloves between processes as well as between substances. A glove that has been in one sensitiser and goes into another bottle has done what a shared pipette would.
14. Dry each set completely before it goes back on its rack, and store it with its own colour together.

Auditing it

15. Once a season, lay every set out and look for an unmarked item, a shared item and an item whose colour has worn off. Re-mark or retire it.
16. Retire, rather than clean, any brush that has been used on two processes, and write the retirement in the log so the next person does not rescue it.
17. Check the trays for chips down to metal, and the tongs for corrosion, and replace rather than repair.

How you know it worked

• Every implement in the room carries one colour and one written process name.
• No brush, tray, tong, funnel or syringe serves two processes.
• The only shared implement is the rod, and it is rinsed at once and inspected before each use.
• No metal touches a silver or a sulphide bath anywhere.
• Only one process’s set is on the bench at a time.
• Paper and negatives live on the dry side and never cross to the wet side.

If a step fails

Step 2, there is only one brush and two processes. Then the room runs one process. A brush shared between two sensitisers is not a saving; it is a defect that appears in the wet processing of the next print and cannot be traced from the print alone.

Step 3, the only brush available has a metal ferrule. Do not use it for silver. Use the rod instead, which is the cheaper implement anyway and uses about a third less sensitiser.

Step 5, a funnel has served two streams. Retire it from the more sensitive of the two, rinse it into that stream’s container, and label the replacement. This matters most where the two streams are an acid and a hexacyanoferrate or a thiocyanate.

Step 6, one syringe was used in two bottles. Both bottles are now suspect. Test the cheaper one and discard the doubt rather than the stock if you can; where a noble-metal solution is involved, record the crossing and expect the fault to appear as fog or as a slow, patchy image.

Step 11, the bead was not blotted and the sheet has dried. Look at the negative before the next exposure, not after it. Crystals at the foot of a coating are what scratch a negative in a printing frame.

Step 13, gloves were carried between processes. Change them and note it. The evidence of the crossing will otherwise arrive as an unexplained defect several sheets later.

Step 15, an item has no mark and nobody remembers it. It is unattributable and it is retired. The scheme only works if an unmarked implement is treated as contaminated rather than as available.

What to record

The scheme itself, on one sheet in the room: process, colour, and the items in that set. Then the audit line each season, with anything retired and why; every crossing of an implement, glove or stream when it happens; and the date a brush entered service, because a brush’s history is the only thing that makes it trustworthy.