How to stop glare on a UV varnish
Specular reflection from UV varnish spreads as white and covers the defects. Use crossed polarizers, or move the lamp so the reflection misses the lens. Do not add exposure to see inside the white. The surround saturates first. Hold the glare down before you set the threshold.
Specular reflection from UV varnish spreads as a white sheet in the frame and covers the defects. Use crossed polarizers, or move the lamp so the reflection misses the lens. Do not add exposure to see inside the white. The surround saturates first. Hold the glare down, then talk about the threshold.
There is no grey inside the white
Varnish acts like a mirror. When the reflection points into the lens, those pixels sit at the top, and pinholes and reticulation become the same white. A tighter threshold has no difference left to read. Move the lamp. The reflection goes outside the lens, the varnish becomes a darker surface, and the texture comes back. If the lamp cannot move, put a polarizer in front of the lamp and one in front of the lens, axes crossed. Specular light is blocked, scatter remains.
Adding exposure makes the white larger. If cutting exposure turns the rest of the frame black, the dynamic range is not enough. Change the angle first. Do not split the difference between all black and all white.
Order of work
| Frame | Do first | Do not do first |
|---|---|---|
| A large saturated white | Change the lamp angle | Add exposure |
| Only a local hot spot left | Crossed polarizers | Loosen the threshold |
| Glare is gone and the defect is still invisible | Check resolution and threshold | Swing the lamp back to the front |
Check at a job change
- Use a varnished sample with orange peel or a pinhole. See whether the defect that was hidden in the white is now visible.
- Confirm there is no large area of pixels at the top.
- On a job with no varnish, remove the polarizers or restore the angle so the frame is not too dark.
