I'm contact printing some 6 x 10 negs from my Kodak VP 3 on expired azo. The paper is really nice and doesn't have any fog, edge yellowing etc. Great contrast btw. I'm using super fix 1:9, Foma stop and Foma paper developer. Anyway, some of the prints have faint pink cloud stains on the back? Nothing on the front? Any ideas on what is causing this?