The blackout leak test

Purpose

To re-establish in tone on paper, rather than by eye, that the room still puts no density on the material it is cleared for — and to date that verdict on the room certificate.

When to use it

After anything that changes what light can get in, or what the material can see: a re-hung window panel, a new door seal or vent, a moved bench, a faster paper, a hand-coated emulsion, the first orthochromatic or panchromatic film the room has handled, a security light opposite, a new season. Yearly otherwise.

Everything is off here, the safelight included: this measures the light that gets in. Testing a safelight measures one lamp; the whole-room fog audit measures every emitter switched on. Run this one first; both are meaningless in a room that leaks.

Before you start

You should already have the room certificate with its material class and date, a timed handling figure, and the reason a room is dark only relative to a material — spectral sensitivity and the room build.

On the bench: two sheets from one box of your printing paper, plus a film strip and its batch-mate where film is handled here; an opaque card; a clock readable without lighting the room, and no phone; black tape and heavy cloth; a torch and somebody outside to walk it; the print baths at their published dilutions and 20 °C; the certificate; the labelled waste containers, silver-bearing among them.

Level A on the classification rubric: tray-strength print chemistry, nothing weighed, heated or wired. Nitrile gloves and eye protection at the trays, closed shoes for a wet floor. The other hazard is the dark: know the door handle by touch before the lights go off.

Procedure

Set the standard

1. Read the certificate. Write today’s date on a fresh block, and what changed, the reason the test is run.
2. Name the fastest material the room will handle, and test with that. ILFORD put their RC papers at roughly ISO 3 to 6; ORTHO Plus asks for total darkness or a deep-red 906 lamp; Kodak’s total-darkness list begins with panchromatic film. The room is cleared for what you test and nothing faster.
3. Time the real handling during an ordinary session, watch in hand: box open to sheet in the fixer. Call it t.

The leak hunt

4. Switch everything off, safelight included, and mask or unplug what cannot be switched. Where a lamp is fluorescent, wait five minutes: the tube keeps glowing.
5. Shut the door, sit down and stay still for twenty minutes. No phone: a screen returns you to the start of the dark-adaptation curve. Kodak give at least ten minutes to full adjustment, ILFORD about fifteen.
6. Sweep in this order: the door frame’s four edges from 300 mm; under the door; keyhole and letterplate; the window sill, then its top corners; the vent; every indicator LED; a glowing dial or clock; the ceiling.
7. Hold a sheet of white A4 against a dark background at arm’s length. If you can see it, the room is not dark, whatever the sweep found.
8. Have somebody walk a bright torch round the outside of the door and window while you watch from inside. It finds a pinhole in a panel.
9. Close what you found: small leaks with black tape, large ones with heavy cloth. Then repeat steps 4 to 8 — a fix that has not been re-hunted is not yet a fix.

The measurement

10. In the dark, take two sheets from one box and notch both. One goes back into its light-tight packet marked CONTROL until step 14.
11. Lay the test sheet emulsion-up where paper sits longest in a session; cover half with the card.
12. Leave the room dark, shut and undisturbed for twice t. Kodak define a safe time as no longer than half the time at which a detectable change appears, so a session of t sits inside it only if nothing shows at 2t. The often-repeated ten-times rule is unsourced and not used.
13. Process both sheets together in total darkness, at the times, temperature and agitation you print at.
14. Dry both, then read them in even light: covered half against uncovered half, and the test sheet against the control.
15. Where film is handled here, repeat steps 10 to 14 with a strip of it, for twice the film’s own handling time, against a batch-mate that never left the box.
16. Write the verdict on the certificate: today’s date, the duration used, the material class passed, and the hour where the blackout depends on the sun.
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

• The line between the covered and uncovered halves of the dry sheet is invisible under even light.
• The test sheet matches the control; if not, nothing above is a room result.
• The verdict names a material — “cleared for RC paper at 30 minutes” — not the word “dark”.
• Where you have a reflection densitometer, read the halves and keep the difference as your own baseline: the course has no sourced density threshold for this test, and ILFORD’s 0.04 belongs to the safelight criterion.

If a step fails

Step 7, the sheet shows and the sweep found nothing. Go to step 8 with the torch, then look for the path you did not build: a keyhole, a letterplate, a loft hatch. Kodak name plywood as looking opaque while still admitting infrared.

Step 9, the leak is overhead. Working at height is the Level B step of the room build under the mixed-level rule; do it there, with a second person.

Step 14, the control is grey too. Not a room result but a fogged box: suspect the paper’s age or storage, and separate the causes with base fog.

Step 14, the sheet is grey and the control clean. A real leak, or the safelight was left on. Check the switch, repeat steps 4 to 9, then repeat with the sheet elsewhere: the difference between two positions gives the direction.

Step 14, one edge or corner is darker. A directional leak, the easiest to find: replace the sheet in the same orientation and the darker edge is the side it came from.

Step 14, it passes at midnight and fails at noon. The blackout depends on the sun. Improve the window, or write the working hours on the certificate and keep to them.

Step 15, the film fails where the paper passed. Expected: the certificate carries both verdicts and the room is cleared for the slower material only.

It passed and prints still show a band. A lighter band is not fog but the enlarger, the easel or the carrier. Read the room that fogs.

What to record

One block on the room certificate: the date; what changed; the material class tested; the paper or film, its batch and the date the box was opened; your handling time and the duration used; where the sheet sat; what the hunt found and how each leak was closed; the verdict for each material; any densitometer difference, marked as your own baseline; the hour where the blackout depends on the sun; and the date the next test falls due. Date it: the verdict belongs to a configuration, and every configuration eventually changes.