Silver nitrate at the coating bench

Purpose

To sensitise paper with silver nitrate and finish with your eyes, your bench and your drain in the state they started in.

When to use it

Any session in which paper is coated, floated or brushed with a silver nitrate solution — salted paper, albumen, an iron-silver sensitiser, a printing-out kit. It is written as an extension of the Part II handling procedure, which still governs the jar, the store and the spill; what this sheet adds is the coating bench, where wet sheets are lifted dripping at chest or face height with both hands occupied.

Before you start

You should already have read the salting and sensitising lab and the Part II lesson, and looked up the strength you are about to make.

Level B, carried by one statement. The substance is signal word Danger with H314 — severe skin burns and eye damage — and H272 as an oxidiser, with acute and chronic aquatic statements. The eye statement is the strongest thing it carries, and the specific warning for this bench is that dripping sheets are a special hazard to the eyes.

• Chemical splash goggles, sealed, not safety spectacles, from the moment the jar is opened until the bench is washed down.
• Nitrile gloves that fit tightly. A loose glove lets solution run inside the cuff while a sheet is held above the tray, which is worse than none. Change one the moment it is contaminated inside, and wash immediately after any contact.
• An apron and long sleeves. The stain appears the next day on the shirt you did not think you had splashed.
• The eyewash procedure is read before the session, not looked up during it.

No respiratory protection is specified, because no step here raises a dust or a vapour — the solutions are made at or a little above room temperature and the substance is not volatile. Crushing caked crystals rather than tipping them invents a dust hazard this sheet did not plan for.

Procedure

1. Cover the bench, stand a tray under everything, and put the labelled silver-bearing waste container within reach of the sink before the jar is opened.
2. Take every piece of metal off the bench: no steel tray, no metal-ferruled brush, no clips, tongs or spoons. A brush bound with thread is the published alternative, because silver nitrate reacts with a ferrule and prints the reaction as a stain.
3. Confirm that no ammonia, alcohol or sulphide is in the room. The course does not make an ammonio-nitrate sensitiser, and an ammoniacal silver bath boiled down can form an explosive solid.
4. Goggles, gloves, apron on. Then weigh or measure, by the weighing procedure, and make the solution up to a stated volume rather than adding water to a weight.
5. Label the bottle immediately — substance, strength as per cent w/v, make-up volume, date, lot — and keep it brown and in a cupboard.
6. Work below face height. Lift a floated or coated sheet by one corner, peel it slowly, and let it drain over the tray rather than over the bench or over you.
7. Hang sheets to dry over a covered floor and not over a walkway.
8. Keep the coating bench and the printing bench apart, and keep the paper box on the dry side.
9. Wipe every splash wet, at once. A dried film of silver nitrate on paper or blotter is an oxidiser in cellulose.
10. Put every rinse — the tray, the rod, the brush, the graduates, the gloves — into the silver-bearing container. Nothing containing silver goes to a drain at any dilution.
11. Bag the solids: blotting paper, spoiled sheets and trimmings. They were a recognised recoverable silver source in the nineteenth century and they are still silver.
12. Do not top a silver nitrate rinse into a container of spent thiosulfate fixer without reading the label: the two throw down a black sludge, which is the same reaction that stains an unwashed print.
13. Wash the bench down, then your gloves, then your hands, in that order, and check your forearms.
14. Cap, wipe, date and update the running volume on the waste container. What may lawfully be done with it is a local question that the disposal caveat sets out and this sheet does not answer. Check your local regulations.

How you know it worked

• Goggles were on before the jar was open and came off after the bench was washed.
• Nothing metal touched the solution at any point.
• Every sheet was drained over a tray, and the drying line ran over a covered floor away from a walkway.
• No splash was left to dry anywhere, on any surface.
• Every rinse went into the silver container, and the solids are in a sealed bag.
• The bottle carries substance, strength, make-up volume, date and lot.

If a step fails

Step 2, a metal item has been in the solution. Discard the bath rather than filtering it: the reaction has already started, and it will print. Retire the item from this bench.

Step 4, the crystals are caked. Tip and break them with the dedicated spatula rather than grinding them. Where the mass will not break, take it to the stock check and decide whether it is retired.

Step 6, solution has run inside a glove. Stop, strip the glove, wash the hand immediately with plenty of water, and record it. The stain will appear over hours; the reason to record it is that repeated absorption is what matters, not one event.

Any of it reaches an eye. Go straight to the eyewash and keep irrigating; this substance’s eye statement is the reason the goggles are not proportionate to the volume. Seek medical advice. The session waits.

Step 9, a spill dried on paper or blotter and went into an open bin. Retrieve it into a sealed bag. This is the domestic fire hazard the Part II lesson names, and it is the one that looks like nothing.

Step 10, a rinse went down the sink. Record it with your estimate of the volume, and move the container closer before the next session. More than nine tenths of the silver you coat leaves the sheet in the rinses and the fixer, so the rinses are not a trivial stream.

Step 12, an unlabelled container is the only one free. It is unknown, and its own procedure governs. Find another.

What to record

The solution: substance, strength, make-up volume, date, lot, and what it was used on. The session: how many sheets, what was coated, and where the drying line ran. The waste line: container, contents, running volume, route and the date the route was checked. And any contact event — a glove, a splash, a stain found the next day — because the record that matters for this substance is a count over years rather than a volume on one evening.