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I understand that Eric found platinum significantly faster with Starphire.
I found cyanotype slightly faster. Gum is absolutely not faster, and
often worser. Some formulas still print OK, but some don't. The ones
giving me most trouble have an opaque black in them (Rowney jet black
gouache). Earth colors supposedly screen UV. But the reasoning (if any) is
out of my league. Tomorrow I buy green glass... >>
Many years ago, before I found out that it wouldn't work, I used a 650 watt
Smith Victor movie light to expose my gums. I remember reading at the time
(please don't ask where) that bichromate was sensitive to UV light and heat
(Infrared?). I remember having to be very carefull sometime breaking up
long exposures to let the glass cool. And even then dealing with something I
thought of at the time as "heat fog" which would give me a flatter and
overall exposure needing longer washes or brushing out the hightlights. What
brought this to mind was your description of flakiness. A very common
problem when I had long exposures, although at the time I thought it was the
thickness of the emulsion. In one of my condensor enlargers is a sheet of
greenish tinted glass i.e. "heat absorbing glass".
Just a thought.
Bernie
Bernard Boudreau