Hi there,
I recently started experimenting with carbon transfer printing. I like brush sensitizing my tissue, for a number of reasons including the fact that I can keep a set of pre-mixed dichromate solutions of different strengths around.
So I mixed a 10% stock solution of potassium dichromate, and from that I made a 6% solution, a 4%, a 2% and a 1% one. I mixed them with distilled water and 90% rubbing alcohol, and kept them in amber glass bottles inside a cabinet at room temperature.
After 3 weeks, the dilute solutions are not orange as they started, but brown.
I pulled a few prints with the brown dichromate solutions, and they look pretty good (for as good a carbon printer I can be), but I don't have a real term of comparison from when the solutions were fresh.
I have read somewhere on APUG that dichromates have a long shelf life, so I was wondering whether the color change is related to a change in sensitivity, curves etc. Does anyone have experience with this?