The whole-room fog audit

Purpose

To measure what a printing session actually exposes paper to. The safelight is one emitter in the room and rarely the worst; this audit puts every one of them through the same test on the same paper, ranks them, and gives the working figure your practice is held to.

When to use it

Once a year, and whenever the room changes what it emits: a new timer, a charger on the bench, a replacement enlarger, a security light outside, a faster paper.

Run it after the two tests it depends on, never instead of them. The room’s leak test measures the room with everything off; testing a safelight measures one lamp. This measures all of them, singly and together, at one sitting.

Every sheet gets its printing exposure first and the safelight exposure second — the “after” end alone, which ILFORD call the more critical. The paired strip belongs to the lamp’s own test.

Before you start

You should already have the room certificate with its leak verdict, material class and date; a tested figure for the lamp; and the reason the after end governs, from the fog limit.

On the bench: paper from one box — one sheet per emitter, one for the whole room, one control and two spare; an opaque masking card; the enlarger; a clock readable without lighting the room, and no phone; developer, stop, fixer and wash at their published dilutions and 20 °C; the record sheet; the labelled waste containers, silver-bearing among them.

Level A on the classification rubric: tray-strength print chemistry, nothing weighed, heated or wired. The hazards are the dark and powered equipment in a room with water in it.

Procedure

Inventory and geometry

1. In white light, write a numbered list of everything that emits light or admits it: each safelight; the enlarger lamphouse; the timer display; every indicator LED — supply, charger, router, extractor, smoke alarm; a glowing clock face; the door edge, threshold, keyhole and vent; the ceiling. Kodak name the lamphouse, lighted dials and pinholes as the three usually missed. Each is one test sheet.
2. Mark the point where paper sits longest, usually over the developer tray. Every sheet is exposed there, and nothing moves again until the audit is finished.
3. Time your real handling during an ordinary session, box to fixer. Step 16 compares against it.

One exposure for every sheet

4. Range-find the grey-tone exposure: a doubling series on one sheet, processed fully, taking the step nearest a light grey — Kodak’s target is a reflection density of 0.25 to 0.50, ILFORD’s about 0.2 to 0.3. Use one and record which.
5. In the dark, cut and notch one sheet per numbered source, one for the whole room and one control, all from the same box.
6. Give every sheet that identical exposure at one end, in one sitting, and label the end “after”. Sheets exposed differently cannot be ranked against one another.
7. Return the control to its packet now, and leave it there until step 13.

Every emitter, the same way

8. With the room dark and every source off, switch on source 1 alone. Lay its sheet emulsion-up at the point from step 2 and, masking with the card, give successive areas 0, 1, 2 and 4 minutes, or Kodak’s 0, 1, 3 and 7. Choose one series for the whole audit and never mix them.
9. Repeat step 8 for each numbered source: one sheet each, one source on at a time.
10. Test the enlarger with its lamp on and the lens capped: that measures what leaks from the head, bellows and carrier, not what comes through the lens.
11. Test the door edge and vent with the corridor light on and, where the blackout depends on the sun, at the hour it is weakest.
12. Last, switch everything on at once for the whole-room sheet. That one describes a session.

Process and read

13. Process every sheet together, control included, in total darkness: full development to the maker’s time and temperature, then stop, fix and wash. Pulling one early makes development a second variable.
14. Dry everything, then read each sheet against its own 0-minute band — dry, edges touching, under an even white light with the safelight off. Record what that light was.
15. On each sheet, note the shortest step at which a difference shows, and halve it. Rank sources by that time, shortest first: that is the order to fix them in.
16. Take the whole-room sheet’s halved time as your working figure and compare it with step 3’s handling time. If it is shorter, the room fails at the practice you actually have.
17. Route the spent baths — developer and stop by the general waste procedure, fixer and first wash to silver-bearing waste — and read the disposal caveat before any leaves the house.

How you know it worked

• Every test sheet carries one grey patch and four bands; the control, a grey patch and nothing else.
• The control matches the 0-minute band of every sheet. Where it does not, nothing here is a room result.
• Each source has a time beside its number; ties usually mean two were on together.
• The whole-room figure is no longer than the shortest single-source one, because exposures add. A whole-room sheet that beats its worst source means something was off that should have been on.
• The certificate carries today’s date, the working figure, and the inventory it belongs to.

If a step fails

Step 1, a source that cannot be switched off. A smoke alarm’s indicator stays lit. Test it anyway; if it fogs, tape matt black card over it rather than removing the alarm.

Step 4, no step shows a tone. Contaminated developer, or the sheet went in emulsion side down: a trace of stop or fixer gives blank prints. Mix fresh developer and repeat.

Step 8, you cannot time four minutes in the dark. Use a clock that does not light the room. A phone face-up beside the tray is another emitter, inside the test.

Step 12, a fluorescent tube was on. Wait five minutes after switching it off before exposing anything else; the tube keeps glowing.

Step 14, the control is grey. Not a room result. Suspect the paper’s age or storage — base fog separates the causes.

Step 15, a difference appears at one minute. A density change of the order of 0.04 after one minute is ILFORD’s criterion for inadequate conditions. Derive no time from it; fix that source first.

Step 16, the figure is shorter than your handling time. Work down the ranking, not around it: move a lamp back, cover or turn a display, seal a leak — black tape for a small one, heavy cloth for a large one, Kodak’s instruction — then re-run the audit, not the arithmetic.

Every sheet passed and prints still veil. The audit tested one position. Repeat at the easel and the paper store, and read the room that fogs.

What to record

One block on the record sheet: the date; the paper, its grade and batch and the date the box was opened; the step series and grey-tone target; the light you read under; the numbered inventory as it stood that day; the first-change and halved times against each number; the whole-room working figure; your handling time; the verdict; what you changed. Copy the working figure onto the room certificate, and onto the lamp beside the lamp’s own — different numbers, and the shorter governs.