With a LOT of help from friends, I have sorted out my fogging problem. I had planned to do a long post to explain the troubleshooting process, but the process has faded into the mists of time (or my mind).
My first and biggest problem was that my darkbox was NOT light tight. Once I gaffer taped all the gaps, voila! 90% of my fogging issues disappeared. Things were still not perfect, though, and so I tried Mark Osterman‘s developer formula. This works much better for me than the formula I have been using. Same ingredients, just different ratios. I also finally caved and bought some proper full-strength Everclear — no more 151 proof or denatured alcohol for me.
I still have some edge contamination problems, but I think that’s just a product of my holder, which appears to be almost unique. I can’t find a book plate-style holder that fits my camera back anywhere, and will probably see if I can get one made to replicate it. It is actually a genius design, holding tintypes on one side and glass on the other.
This is one of my successful plates after making all the changes. The spots are from a bad developer pour (I am still working on my technique).
I bought some sandarac varnish from Bostick and Sullivan, and I much prefer this over the polyurethane spray I was using before. It’s worth the extra money, and–bonus!–it makes the house smell like lavender. It’s terribly messy, though.
Yesterday I shot two great ambrotypes (upcoming as soon as they’re varnished), as John Coffer advised that perhaps my trophy aluminum was contaminated. It has happened to him before that a student couldn’t figure out why he couldn’t get a clear plate, and it turned out to be the aluminum. It may have indeed contributed to my problems but there were several variables.
I can’t wait to show you the ambrotypes.