Re: Re: Carbon Printing UV/Cool White
s carl king (sanking@hubcap.clemson.edu)
Mon, 8 Jan 1996 16:29:00 -0500 (EST)
>
> At the moment, though working with a bad emulsion, I'm getting a
> reasonable blue and a few steps under the 21-step with the BL bulbs
> (though requiring about twice my usual exposure time -- 6 minutes vs.
> normal 3 minutes), but have not been able to get a SINGLE step in
> cyanotype with the cool white bulbs-- which jibes with my long-ago tests
> showing the cool white bulbs much MUCH slower on cyanotype than the black
> lights. I'll post details of the system I've devised (not as "cyantific"
> as Sandy's, but OK I think) and actual results shortly.
>
When the results are as conclusively different as you describe between
the two bulbs your *eye-balling, cyantific test* is as useful as any
results from densitometer reading. BTW, I have another informal report
from someone on the list which suggests that even the daylight tubes
are much slower than BL tubes with cyanotype. So, as I suggested, maybe
a crow snack rather than a full meal will be sufficient atonement.
> Meanwhile, two other points. The spectral-power distribution chart
> of the *daylight* bulbs arrived from GE. It's not easy to read, as it's a
> black and white photo copy made from a color original. Nevertheless, it's
> quite apparent that about HALF the energy in this bulb is in the 400
> to 500 nm range, the rest from 500 to about 650. The biggest "spike" is
> at about 440 nm, with another at 400 and one at 550.
>
You sure have more pull than me. I have been trying to get this all week,
or even find someone to talk to on the subject. The news that over half
the energy of the daylight bulbs is in the 400-500 range, with the biggest
spike at 440 nm, together with Klaus Pollmeier's mention than an older
(1926) German version of Eder found that the maximum sensivity of
dichromate sensitized colloids was 450 nm (for daylight) and 420 (carbon
arc), makes me very optimistic that the daylight tube will
work very well in my conditions in carbon printing.
That said, I am not jumping to conclusions. Apparently Klaus is working
with bulbs fairly similar to mine (Phillips TL 20W 05* UV tubes and
is getting good contrast with 1%-2.5% potassium dichromate and
1%-3% ammonium dichromate in water and alcohol 1:1, using
Hanfstaengl carbon tissue.
Meanwhile, my main obsession at the moment is balancing a 3-color
carbro tissue set with some recently acquired pigment samples. I
am now in the 6th formulation and the transfered step tablet still
looks very contrasty and green!!!!!
Sandy King
Sanking@hubcap.clemson.edu