From: Judy Seigel (email@example.com)
Date: 10/18/01-12:21:50 AM Z
On Wed, 17 Oct 2001, Sandy King wrote:
> It is known that many gummists, past and present, engage in such
> practices as mechanical development, forced development with water
> sprays, rubbing the image with sponges, brillo pads and other
> abrasive tools, etc. etc. Some have even been know to illustrate the
> borders of their prints with hand drawings, painting, and various
> other kinds of decorative information!!! Such practice (excluding
> the latter) *distort* the basic sensitometric principles of colloid
> processes so it is hardly surprising that some of the photochemical
> laws described by Kosar for photosensitive systems do not apply in
> your case.
Unh unh, you can't pin that on me... When I cite "curve" of a gum print,
I mean an absolutely unmanipulated 21-step -- emulsion applied, smoothed,
dried a standard time, exposed under 21-step for standard time (mine
usually 3 minutes) and developed face down untouched by human hands in
still room-temperature water for one timed hour.
In my experience, although it is POSSIBLE to get a straight line in a 21
step, it has to be a very pale tone. Otherwise bottom steps will be very
close, top step have a BIG jump.
> Virtually all light systems emit spikes outside of the area of major
> radiation of the light source, and virtually all photographic systems
> have some sensitivity outside the area of greatest sensitivity. That
> is why we can print carbons and gums with light sources which emit
> little or not UV light, i.e. daylight tubes. The bottom line,
Which as I recall worked with carbon, not gum. I think lumping the two
together is mistaken in many of these respects.
> however, is that as the wavelength of the exposing light falls into
> the UVB range, and lower, the contrast of the image decreases. This
> is a basic photochemical law of dichromate colloid processes.
Ah, law... these laws are entirely manmade (probably in this case, tho
maybe "human made" is nicer). So did you test that with gum? UVB is "ultra
violet blue"? Did I mention, by the way, that different gums produce
different contrasts? Did I mention that different proportions make
different contrasts? Did I cite andsoforth?
> >> Speed of the printing source, within a certain range of wavelength
> >> (say 300-450 nm) appears to be more dependent on wattage than the
> >> exact wavelength of the light source, or so my tests show.
> >Oh yum, yum... Did you put those tests on the list?
> Not yet, but coming soon to a theatre near you!!
> BTW, I must correct a previous observation. As you might recall, in
> comparing the basic pros/cons of my bank of BL tubes with a new metal
> halide light system recently acquired, I stated that contrast was the
> same with the two systems. In fact those earlier observations were
> incorrect. Further, more definitive tests have shown that the ES of
> carbon prints made with the metal halide unit is about log 0.30 less
> than that of prints with the BL unit. That is, the MH unit is in fact
> a more contrasty light by more than the equivalent of one full
I found that exposure with the halide bulb of the NuArc was, ALL THINGS
BEING EQUAL, somewhat contrastier than with the fluorescents. The thing is
that in gum, all things are so RARELY equal....even entirely unmanipulated
there are infinite variables. Then if we're talking about multi-coat gum,
which we usually are, the variables increase exponentially. However, I can
see that in other (more finite) media, bulb contrast may be defining.
I think I mentioned that I found the daylight bulbs made MUCH contrastier
cyanotypes, but took about 2 hours. I contemplated alternating bulbs, but
never got around to it.
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