Am experimenting with applying asphaltum to the back of clear glass ambrotypes. I used a roller to apply a 50/50 asphaltum/mineral spirits mix. Needed to do about 5 coats to get it this dark, but it seems to be working. Did two trial types with these so so practise plates. Type one I applied the asphaltum directly to the collodion, type 2 I varnished the plate then applied the asphaltum.
