How's this for "no apparent reason": I've been unable to print formulas
that were great last year. Racked my brains. Same everything -- what was
different? THE GLASS! That infernal *expensive* Starphire glass on the
vacuum frame, replacing the one I broke. I did some tests with 21 steps,
which showed the strip under the Starphire much flakier, which was the
problem. Couldn't be POSITIVE from such small sample. Today cut a large
sheet of paper in half, coated each half from same batch of emulsion,
exposed for 100 units, the first one under the Starphire, the second one
under a piece of green glass the same thickness. True, the one under the
green glass didn't have vacuum, but I've printed these formulas for years
with vacuum so ruled out that variable.
Now do not ask me why -- TELL me why. I did not mix up the labels. The
one under the Starphire glass was LESS exposed and the emulsion was far
far flakier..... flaked off within the hour. The one under the green
glass was exposed more, took significantly longer to develop, and then was
much less flaky.
The only surmise I can make is that for gum printing there are other
factors at work beyond straight UV, or lack of same. Some differential
between the glasses is having this effect. Starphire's fancy charts
showing how much more UV comes through do not address this "X" factor.
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...
> are many very beautiful gum prints in this world. I will take a gum print
> over a silver any day of the week so if I offended any gum printers
> consider the statement retracted.
That "X" factor must be why gum is so beautiful..... And of course, as we
see, it's soooo sensitive. Far above klutzy old cyanotype and platinum...
Judy