When you should measure with a polarising filter
Polarization is ISO 13655 M3. It knocks down gloss on wet ink so a wet reading sits closer to dry density. That is useful for watching ink film in process. If acceptance is written as M1 or M2, an M3 number cannot close the job. On or off, the whole job stays consistent.
Polarization is ISO 13655 M3. It knocks down gloss on wet ink so a wet reading sits closer to dry density. That is useful for watching ink film in process. If acceptance is written as M1 or M2, an M3 number cannot close the job. On or off, the whole job stays consistent.
It solves gloss, not hue
Wet ink is brighter than dry. Density reads low, it looks like not enough ink, you add ink, and after dry it is too heavy. Polarization blocks the specular part, so wet density sits closer to dry density and the operator can hold film. It does not read a reddish ink as not reddish. Hue still comes from the spectrophotometer, and from the non-polarized condition the contract names.
So polarization is a process tool. If the OK sheet and customer acceptance are M1, that last reading is M1. You cannot convert press M3 density into the customer’s colour difference.
When to add it
| Purpose | Polarizer? | Against what |
|---|---|---|
| Hold density while wet | Yes, M3 | Only an M3 density target |
| Colour difference to an M1 OK sheet | No | M1 Lab* |
| Compare wet and dry | Both on or both off | Not one on and one off |
When you record, write
- Write M3 or “polarized.”
- Do not put an M3 number in colour-difference acceptance.
- If you switch the polarizer off mid-run, break the density trend and start a new record.
