Weighing and handling developing agents

Purpose

To get a stated mass of a developing agent from a jar into a mixing vessel without breathing it, wearing it, or leaving any of it on a bench.

When to use it

Whenever a developing agent is weighed as a powder — metol, hydroquinone, phenidone, an ascorbate, p-aminophenol, pyrogallol or catechol. It is a Level B extension of the weighing procedure, which still governs the balance, the tare, the weighing by difference and the reading you write down. What this sheet adds is the controls for these substances.

It stops at the mixing vessel. The dissolving order and the make-up belong to mixing a developer and to the formula’s own page.

Before you start

You should already have read the safety data sheet for the substance in your hand and recorded its version and date, by the sheet procedure. These agents differ from each other more than their common name suggests: metol is signal word Warning with a skin-sensitisation statement, hydroquinone is Danger with serious eye damage and a suspected-mutagenicity statement, and pyrogallol carries harmful in contact with skin, harmful if inhaled and suspected of causing genetic defects at every reporting notifier.

Level B, and the criterion is fine powders that must not be inhaled, with skin sensitisation beside it. The controls, in full:

• Weigh in a tray, in still air, with the window shut for the minute you are weighing and open again afterwards. A draught at the balance lifts powder.
• One jar open at a time, and capped before the next is opened.
• Nitrile gloves, single-use, at the thickness the safety data sheet asks for or 0.2 mm where it gives no specific advice.
• Eye protection, and splash goggles rather than spectacles where the sheet carries an eye-damage statement rather than an irritation one.
• A particulate mask to the specification the sheet gives.
• No photographic paper or film open in the room, and nothing eaten or drunk at the bench.

The staining agents have an alternative route and it is named here rather than in the procedure. Pyrogallol and catechol are readily absorbed through skin and are handled to the standard their own pages set. Take the substitution — a non-staining developer of a different family — as a matter of course if you are pregnant, if you have any skin condition, or if you are working in a shared kitchen, and say in the record which route you took.

On the bench: the balance in its own tray, on a level, still surface; a dedicated spatula per jar; the weighing vessel; the mixing vessel; a damp cloth; the notebook, open.

Procedure

1. Decide the route first: bought liquid chemistry where it exists, a non-staining substitute where the staining agent’s controls cannot be met, or the weighing below.
2. Write the target mass and the substance’s full name and form in the notebook before the balance is switched on.
3. Put the gloves, the eye protection and the mask on, and put the balance in a tray.
4. Shut the window and let the air settle.
5. Open one jar. Check its label against what you wrote: same substance, same form, same hydrate.
6. Work at bench level rather than eye level, so any plume stays below your breathing zone.
7. Add the solid slowly with that jar’s own spatula, and stop where you stop. Scraping some back out puts it into the air.
8. Weigh by difference for anything hygroscopic, static-prone or expensive: weigh the jar, tip some out, weigh it again. The substance never sits exposed on a pan.
9. Record the actual reading before anything else happens.
10. Cap the jar and return it to its group before the next one is opened.
11. Transfer to the mixing vessel and rinse the weighing vessel into it with part of the water the formula already calls for.
12. Dissolve in the order the formula gives — a developing agent that is only slightly soluble in a sulphite solution with no alkali in it may simply refuse to dissolve if the sulphite goes first.
13. Clean every trace wet, with the damp cloth, and wipe the balance, the tray and the bench before the mask comes off.
14. Wash your hands before you touch anything else, and open the window again.
15. Label the result immediately by the labelling procedure, with the version identifier the batch will be known by, and bottle the spilled or surplus solid separately. Check your local regulations, which govern its route.

How you know it worked

• One jar was open at a time and each was capped before the next was opened.
• The mask stayed on until the bench had been wiped wet.
• The notebook carries the reading you got, not the target, with the form of the substance beside it.
• No paper, film or food was in the room, and no powder is visible anywhere on the bench.
• The route you took — bought liquid, substitution, or weighing — is written down.

If a step fails

Step 1, the safety data sheet asks for controls you do not have. Then the step is not classified for you today. Buy the substance as a solution if it is sold as one, or defer the batch. That is the same conclusion the published guidance reaches from the other direction.

Step 5, the jar’s label does not match what you wrote. Stop. A jar whose identity you cannot confirm is an unknown, and it does not go into a developer on the strength of what the shelf says.

Step 7, you overshoot. Do not scoop any back. Either scale the whole formula to the mass you have, which is arithmetic rather than judgement, or start again with a clean vessel and route what you weighed out by general chemical waste.

Step 7, the powder creeps or leaps off the spatula. Static. Go to step 8; that is why the step is there.

Step 8, the solid is caked, damp or has lost its shape. It has taken up or given up water and it is no longer weighable to a stated strength. Take it to the stock check and decide whether it is retired.

Step 13, more than a smear has been spilled. Stop and use the solid spill procedure, which is written for a quantity this one is not. Never brush a dry spill: it re-suspends the whole of it.

A glove tears, or powder reaches skin. Change the glove and wash immediately. Sensitisation is cumulative and individual, and once acquired it does not go away — so the event is recorded even when the quantity is trivial.

What to record

Per substance and per batch: the date; the substance, its form, its supplier and lot; the safety data sheet’s version and date; the target mass and the mass actually read; whether it was weighed directly or by difference; the balance used; and the route taken at step 1. Then the batch’s version identifier, written on the label before the bottle is filled, so that a curve or a print made from it can be argued with later.