Tonight I am experimenting with different type paints for backing ambrotypes. Many acrylics, a tempera and a washable paint.
Thinking
the best options at present will be to use a high end more expensive
archival artist level black acrylic paint with a double varnish applied
first. I am also eager to see how washable black paint works.
Theoretically you could wash the paint off with the double layer of
varnish protecting the collodion, at some later date. The goal is to
find a working method for the larger clear glass ambros of the future,
up to 35x35 inches.
Will also give asphaltum another try in the coming weeks. My initial work with that material was so so.