How to compare a wet reading with a dry reading
A wet reading and a dry reading can be subtracted only on the same instrument, the same M condition, the same backing, and the same patch. Polarizer on while wet and off after dry is not dryback. Align the conditions first, then talk about how much drying changed the color.
A wet reading and a dry reading can be subtracted only on the same instrument, the same M condition, the same backing, and the same patch. Polarizer on while wet and off after dry is not dryback. Align the conditions first, then talk about how much drying changed the color.
What wet ink adds is gloss
Fresh ink is shiny. The instrument treats part of that gloss as color. That is why some people add polarization for a wet reading — M3 — to knock down specular reflection. If you switch to M1 after it dries, the change you see mixes drying with a filter change. Split those: either both readings use M3, or neither does.
The OK sheet is usually dry. A wet M1 against a dry OK sheet can fail only because it is still wet. A wet M3 against a dry M1 OK sheet does not hold either. Process control can use wet readings. Acceptance follows the contract: dry or wet, and which condition.
Which two numbers can be subtracted
| Wet | Dry | Subtract? |
|---|---|---|
| M1, white backing | M1, white backing, same instrument | Yes, that is dryback |
| M3 | M1 | No |
| This instrument | Another instrument | No, compare instruments first |
| Black backing | White backing | No |
When you record, write
- Both times: clock, M condition, backing, and instrument.
- Different conditions: do not subtract.
- Against an OK sheet, write whether that sheet is dry or wet.
