Help with fogging for pt/pd printing (dichromate contrast control)
I am having problems with fogging (gray mottling) in my highlights of pt/pd prints. I am using potassium dichromate in my potassium oxalate developer for contrast control. In the past, I used NaPt for contrast control with no problems for straight Pd printing. This is my first foray into printing with both Pd and Pt. Do I need some type of restrainer in my metal solution? Currently, I am using the following for an 8x10 print:
1 ml FO (relatively fresh ~1 month)
0.5 ml Pt
0.5 ml Pd
developed in potassium oxalate (1L + 2ml of 10% potassium dichromate)
Exposures are ~400 units on a Nuarc and I am getting mottled highlights even when I cover the coated paper with foil. The degree of mottling seems to coincide with how long the coated paper sits out suggesting it may be sensitive to spurious UV in the house.
Any thoughts or ideas?