I recently produced this tintype of my friend Nicole Haagensen. It takes about an hour to produce each plate and I'm still struggling with this process. Immediately after I develop, fix and rinse I shoot these with my dslr to preserve the image. Sometimes as soon as 30 minutes later the my plates are developing black spots. I know I'll need to mix fresh chemistry soon to get my plates archival again. The trick is finding out which chemistry is causing the problem.