<< Another interseting observation he has made concerns print times and
contrast. He says he got a Palladio light bank and his time went to 1/4 of
what they were before but the contrast went way down. We suspect that the
contrast may in fact be related to the print times and that the blue gel
just increases the print times which in effect, increase the contrast.
>>
>From the description it seems likely that the blue gel is indeed affecting the
contrast. I think the emulsion has different sensitivity to different
wavelengths. Since I cannot verify it, this is just a guess, but I think it is
a reasonable guess. This is the "ups and downs" along the spectral sensitivity
curve that Dick mentioned when we talked about the pyro development. With the
blue gel you cut down some the light of some wavelength, so the response could
well be different. It is the same principle in variable-contrast paper and
magenta contact screens.
In general I do believe that most emulsions has different sensitivities to
different wavelengths, that is why when we use different light sources (bl,
uv, plant grow, etc.) we not only get different exposure time, but also
different contrasts.
Maybe this is a good connection to the pyro thread for me to explain myself
because I was misinterpreted as saying that the yellow stain did not give any
difference in contrast. I did not say that. I said that *IF* contrast were the
thing that we were after, we could probably achieve the same result with
silver alone, especially if we were to do some special development tests for
our negatives.
But this blue gel thing is significantly different. I personally think it is
much more worthwhile to pursue because if it really works, it means that you
can alter the contrast of an *existing* negative. You can even use gels of
different "blueness" to change the contrast differently.
Just my 2 cents.
Dave