Handling a selenium toner and its waste

Purpose

To open a selenium concentrate, work a dilute bath from it and put every millilitre of the result into a labelled container, without an acid ever entering the room.

When to use it

Any session in which a selenium toner concentrate is opened, diluted, used or bottled — including a session that only bottles a working bath at the end. It governs the substance rather than the picture; the sequence around the print belongs to the toning session.

It does not cover making a toner from elemental selenium. That route begins by boiling selenium powder in sulphite solution, and the chemistry lesson explains why this course buys the bottle instead.

Before you start

You should already have read the selenium chemistry and the safety data sheet for the bottle in your hand, because the two products in the corpus are not classified alike: one is acute toxicity category 4, the other category 2 at signal word Danger. Record the sheet’s version and date.

Level B. Impervious gloves to EN 374, single-use, from the moment the cap comes off until the last container is capped; eye protection with side protection to EN ISO 16321-1, and splash goggles for the decant; an apron. Run the ventilation check before the session — general ventilation with a through draught, running throughout, not switched on when the tray starts to smell.

No respiratory protection is specified, and the reason is on the lesson: no source read establishes what a working bath puts into the air, so the control is dilution of the room’s air rather than a filter chosen against an unnamed contaminant.

On the bench: the graduate standing inside a spare dish; the toner tray; a dedicated funnel; non-metal tongs; the labelled waste container, open, before the cap comes off. And no acid anywhere in the room — the stop bath from the printing session leaves before the bottle is opened.

Procedure

1. Take the acid stop bath, any acid or rapid fixer and any acid clearing bath out of the room, and check the waste corner for an acid container as well.
2. Put the gloves, the goggles and the apron on before the cap comes off, not after.
3. Stand the graduate in a spare dish and measure the concentrate into it there. This is the most hazardous half-minute of the session.
4. Add the concentrate to the water rather than the water to the concentrate, at the dilution the maker publishes, and record the dilution.
5. Bring the bath to the maker’s working temperature and record the reading you achieved.
6. Cap the concentrate and take it off the bench before the first print goes in.
7. Handle every piece in the bath with tongs, not fingers, and change any glove that gets solution inside it rather than wiping it.
8. Keep the tray’s own dedicated funnel with it, and never let it serve another bath.
9. At the end, decide between keeping and discarding. A full capped bottle keeps a working solution for months where an open tray gives it days, so bottling the bath is usually the smaller waste stream.
10. If you keep it, label it with the dilution, the date, and what it has toned, because an aged bath works more slowly and is a different bath.
11. If you discard it, pour it into its own labelled container through its own funnel.
12. Add every stop-bath change and every rinse that followed the toner to the same container. These are the largest volumes of the session and the easiest to lose.
13. Put the rewetting fixer baths into silver-bearing waste instead: they are a different stream.
14. Wash the tray, the graduate, the funnel and the tongs into the selenium container, not into the sink.
15. Cap, wipe the outside of the container, top up its running-volume line and add the date.
16. Take it by a route you have checked. The published guidance for a used selenium toner withholds every route but a household hazardous waste collection facility or a licensed hauler, and what is lawful where you are is settled by the disposal caveat and your own authority.

How you know it worked

• No acid was in the room at any point, and none is in the waste corner beside the selenium container.
• The concentrate was decanted once, over a tray, with goggles on, and capped before printing began.
• Nothing entered the bath that was not lifted out with tongs.
• The selenium container gained every stop change and every rinse, and nothing else did.
• The bottle you kept carries its dilution, its date and what it has toned.
• The ventilation ran from before the first pour until after the last cap.

If a step fails

Step 1, an acid bath is found in the room after the toner is open. Cap the toner, take the acid out, and only then carry on. Acidifying a selenium salt is the one route to hydrogen selenide this bench can create, and its exposure limit is far below anything a darkroom can detect.

Step 3, the concentrate is spilled. Leave the tray to contain it, put on new gloves, and absorb from the edge inwards into the selenium waste container by the spill procedure. Do not wash it towards a drain to dilute it.

Step 4, you added water to the concentrate. The bath’s strength is now unknown. Do not correct it by addition: route it to the container and mix again from a measured volume.

Step 7, a glove has solution inside it. Change it and wash the hand, and note it in the log. Skin sensitisation is cumulative and does not scale down with the volume that reached you.

Step 11, the only free container has held something else. Do not use it. A part-used bottle whose label you did not read is exactly how an acid meets a selenium waste — treat it as unknown by the unlabelled container procedure and find another.

Step 16, your authority does not accept it. The container stays capped, labelled and in its tray while you find one that does. Acceptance varies between neighbouring authorities, and a sealed labelled container is a solved problem for weeks.

What to record

The product, its safety data sheet version and date, the dilution, the working temperature achieved, the volume made and the volume bottled, what the bath has toned and on what date, the ventilation arrangement actually running, and the waste line: container, running volume, route, and the date you last checked that route. Where a glove was changed or a spill occurred, that goes in too — the number that matters afterwards is how often, not how much.