Re: Carbon Printing UV/Cool White
s carl king (sanking@hubcap.clemson.edu)
Thu, 4 Jan 1996 19:41:27 -0500 (EST)
>
> I wonder about the volume of sensitizer and the surface area sensitized.
> When I was doing tricolor carbon I found I had to use a one-shot sensitizer
> for constant results as the third sheet had significantly more contrast and
> less speed than the first, especially with a weak concentration of
> dichromate sensitizer as the dichromate ion was absorbed gradually as the
> sheets went through it. This was a serious problem with low concentrations
> of dichromate, e.g., 1% although I never went below that.
>
Nine (9) 1X5" strips of carbon tissue were sensitized in two sessions, using
five separate 5X7 trays. Easy was sensitized separately, using 3 ounces
of fresh sensitizer, for 3 minutes. The nine strips were dried
together. Each was labeled before sensitizing according to intended use.
>
> > b) The same batch of carbon tissue was used for
> > all tests. This was a warm brown tissue made=20
> > from 3 parts Carmine Crimson, 4 parts Brown, 3
> > parts Primary Yellow, and 2 parts Sumi Ink=20
> > concentrate.
>
> This is a fairly low contrast color to start with.
>
My experience with this tissue is that it is fairly high in contrast. After
all, that is 12 grams of pigment per 1000 ml of coating solution, including
two grams of very strong Sumi Ink concentrate. Still, the color does
introduce a variable that could have been eliminated by the use of a
nuetral black tissue.
>
> How "fresh" were the tubes? New, old?
>
The UV tubes are about 3 years old. How many hours they have been
used is hard to say, but I only use them for carbon printing and
I have done more carbro in the last 3 years than carbon. I would
estimate they have some 300-400 hours of use. The GE Cool White
tubes were new. >
> > d) Exposure was 20 minutes, in all cases enough =09
> > to produce two steps of maximum density.
> ..
>
>
> How much time (hours?) did it take you to go from the first test to the
> last one?
>
>
This is what I did. After the 9 strips were dry I put three each in
a ziplock bag and froze, in anticipation of running essentially three
exposures. What I failed to mention was that each set of exposures
involved three strip simultaneously on three separate Kodak #2 step
tablets. This introudes one variable I failed to mention, however
before exposure I measured steps 1, 10 and 20 of each step tablet and
there was no difference greater than .04 which I believe to be of
no consequence. Thus, the first set was exposed soon after the tissue
was dry, and the other two sets were done at intervals of about
one hour, but with tissue frozen during the interval.
>
> ..
> >2) When the tissue is sensitized with dichromate solutions of 1% or more =
> >there is a strong suggestion that a combination of UV and Cool White tube=
> >s is more effective than either along. I have conducted some further test=
> ^^^^^^^^^^^
> effective in what way?
>
What I mean by effective is that the combination allows the use of
reasonably strong dichromate solutions, a beter guarantee of even
results than the weak solutions necessary with the UV light alone, yet
is slightly more efficient in terms of speed than the Cool White tubes
used by themselves. I am now very interested in repeating parts of this
experiment with the daylight tubes used by Davis.
>
> Most definitely, which is why I seldom used less than 2%. The sensitizing
> time is also very important; perhaps more when dealing with weak
> concentrations. This said, I don't see how the latter part of your
> statement affects the previous part.
>
>
Understood, the latter part is an observation based on past experience, which
is not demonstrated in these tests.
BTW, I have long been curious why my sensitizing solutions with 350na tubes
seem to be so different (requiring such low percentages to achieve
good contrast) from what is described in the literature. Do you have
any knowledge of others actually working in carbon with these or similar
tubes? I would be very interested in knowing what kind of strength
sensitizer they find effective.
>
>
Sandy King
Sanking@hubcap.clemson.edu