Mixing a developer from raw chemicals

Purpose

To make one litre of a named developer, at a version number, from solids you weighed yourself — and to leave behind a record from which somebody else could rebuild the same bottle.

When to use it

Whenever a developer is made up from raw chemicals rather than from a packet. Diluting a stock or a concentrate is a different procedure and starts at a bottle.

Before you start

You should already be able to read a formula and say which hydrate each mass belongs to, and to assign a version code, both from reading a developer formula; and to mix to a final volume, from the commissioning lab.

The weighing step is not at the level of the rest of this procedure, and this is where that is said. The session is Level A once everything is in solution, because what is on the bench is then dilute liquid handled with gloves and eye protection. Four open jars of fine powder are not: the classification rubric assigns a level to an operation, and its Level B criterion of fine powders that must not be inhaled is exactly what step 5 is. So step 5 is worked at Level B controls inside an otherwise Level A session — a tray, still air, one jar open at a time, gloves, eye protection, a particulate mask, and no film or paper open in the room. Read the encyclopaedia entry for every agent you are weighing first; some carry classifications that decide whether you should be weighing them at all.

On the bench: the arithmetic done and checked; a balance reading to 0.01 g, verified today by the bench check; a spatula; a shallow tray; jugs and cylinders; a thermometer; a pH meter calibrated today; two bottles, opaque if you have them, labelled before they are filled; the notebook and the version record.

Procedure

1. Assign the version code before anything is weighed, and open a record against it. Anything that changes — a hydrate, a water, a mixing temperature — is a new version, not a note in the margin.
2. Label the bottles and the waste containers.
3. Draw the water and let it stand a few minutes. Mains water is highly aerated, and dissolved oxygen is consumed by the developing agent before you have used any of it.
4. Set the bench out: tray, balance, spatula, the jars closed, jugs, cylinder, thermometer, with the waste containers beside the tray rather than in it.
5. Weigh every mass before dissolving anything, into labelled containers, in still air with the window shut and the mask on, one jar open at a time, recording each reading to the balance’s resolution as you take it. This is the step described above.
6. Close every jar, then open the window and put the mask away. A draught over an open pan scatters powder around a room, so the order of those two is not interchangeable.
7. Warm the water to the temperature the formula states and check it with the thermometer.
8. Where a historical formula calls for water above the 50 °C Level A ceiling, do not silently modernise it and do not ignore it. Work out from the encyclopaedia’s solubilities whether every dissolution in the procedure is possible below 50 °C; if it is, work at 45 to 50 °C and record it as a stated deviation with its reason, leaving the source’s own figure printed as the source wrote it.
9. Dissolve in the order the formula gives, and for the reason it gives: the developing agent first, in warm water with no alkali present, because it is only slightly soluble in a sulfite solution that has no alkali in it and because bare alkali oxidises it while it dissolves.
10. Then the preservative, then any second agent into that preserved solution, then the alkali last. No agent stands in unpreserved alkali at any point.
11. Wait each addition out completely — no crystals, no haze held up against the light — before the next. Give it the stirring it needs rather than the stirring you planned.
12. Make up to the final volume with cold water, stir, and note the temperature and the time.
13. Bring the batch to 20 °C, or as close as the room allows, and measure the pH by its own procedure. Record the temperature beside the reading.
14. Fill each bottle as full as it will go, leaving only a small air space — enough for the solution to expand, not enough to store air against the developer.
15. Cap tightly, and not with a glass stopper: the alkali tends to make them stick.
16. Write the label — formula, version, date and time, volume, who mixed it, the measured pH with its temperature, and the words that keep it out of the kitchen. Store cool and dark.
17. Route the rinsings and any surplus to the developer waste stream by the general waste procedure, never into a container holding acid or fixer, and under the disposal caveat.

How you know it worked

• Every mass in the record is a reading you took, not a target you aimed at.
• Nothing was dissolved out of order, and each addition was fully in before the next.
• The finished developer is clear and near-colourless. Straw or brown is oxidation, and it happened during mixing.
• The bottle is full, capped, dated, versioned and carries a measured pH.
• The version record would let a stranger rebuild this bottle.

If a step fails

Step 1, you are mixing a variant of something you already have. Give it a new code now. Two bottles sharing one code is the failure this whole record exists to prevent.

Step 5, a mass is out by more than the formula’s tolerance. Tip it back, clean the pan and reweigh rather than correcting by addition. If the balance is drifting, stop and run the bench check.

Step 9, the agent will not dissolve. The water is too cool, or the sulfite went in first. If the sulfite is already in, the batch cannot be rescued by warming: start again, and record why.

Step 11, the solution goes yellow or brown while you mix. Aerial oxidation. Finish the batch, measure its pH, label it with what you saw, and use it for work you can afford to lose. The next batch gets warmer water, faster stirring and the alkali later.

Step 12, you overshoot the volume. Record the actual volume, recalculate the strength from the masses you weighed, and label that. An overshoot you recorded is a developer of known strength.

Step 13, the meter will not settle. Record the range you could resolve honestly rather than a spurious figure. A reading of “between 8.5 and 9” is worth more than a fabricated 8.63.

What to record

The version record, filled in: the code; the formula and the publication it came from; every weighed mass; the water and its source; the mixing temperature, with any deviation and the reason for it; the order actually followed; the final volume; the measured pH with its temperature; the date, the time and the mixer. The formula version record worksheet carries the fields, and the label repeats the short version of them.