Laser burn mark archival test
The darker paper is a thin, emulsion coated paper made by Kodak which is now discontinued. But the CLF have a lot of it left over and it is very useful to make these tests.
I’ve treated some with photographic chemicals to try and preserve the marks. In this photo they’re on my windowsill where they will get direct sunlight for half the day. This should give them a good test for durability.
The two brighter bits of paper are photographic resin coated black and white paper. These went through a stop and fix bath so should be stable now.
All these burn marks are a combination of actual burns (with carbon marks which will obviously be quite permanent) and a purple/brown colour. The colouration is purely from light hitting the photosensitive paper. Black and white photographic paper will gradually develop slightly if left in light, these marks were made on the raw paper in the light so all the paper was exposed, but the huge intensity of the laser turns the paper darker without any developing solution being needed.