How to make a faster unwashed emulsion?
I made an interesting emulsion following instructions for an unwashed bromide emulsion found on "Silver gelatin" book.
20 g gelatin
16 g potassium bromide
125 ml water
mix sol. at 50°C
20 g silver nitrate
raise temp. at 40°C
mix B into A at slow rate
the emulsion is supposed to be ready right after digestion is complete; no washing or additives are strictly required
This emulsion works fine for me. Requires two coatings for a contrasty image. ISO rating has been a little problematic. Under the enlarger it needs at least 120" F4 to print its deepest black. Average exposure required is 160-240" at F4. In one word: SLOW.
I was attempting to use the same emulsion for glass negatives. The emulsion sticks very well to glass without subbing. A little sanding of the edge of the glass helped.
The problem is its really poor sensitivity to light... Which is probably ISO 3. But since it is especially sensitive to Blue and UV, the ISO drops when shooting in artificial lighting. Is there a way to make it faster? Say ISO >10? Should I modify a little the above formula? Another solution I've considered is to dip the plate into developer right before exposure, pretending it is a wet plate. Kalotypes work in a similar way... but then the obvious advantages of a dry plate are gone.
Any suggestions or recipes for other unwashed emulsions? I'd prefer to stick on unwashed emulsions. Handling a more complicated emulsion-making process would be too much for me now.