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Thanks for this Marek. It is always heartening to
see someone else testing things for the heck of it and you are the test King!
Bleaching, pinhole, yupo, solarization...
I love how Picasa has that magnifying glass option so we
can really get close in to the test strips. Almost like being in your
dimroom.
I like also how you can see on your wedges where the
numbers are dull with too little exposure.
So do you think you will use the flash technique in your
practice in general or only with dense film negs?
One question: did you clear your step wedges in
potassium metabisulfite or whatnot? It can be hard to determine
how long gum's tonal range is at times because of the fact that the dichromate
gets darker and darker and darker with exposure and gives a bit of a false read
to the step wedge when, in fact, gum has reached "max black" before the
dichromate has reached "max brown". I don't ever clear unless I am doing
step wedges. I find that gum has a 4-6 stop range, with 6
stretching it. This is certainly longer than some books that say it has a
2 stop range, though, and it looks like from your step wedges you are getting
more like the 4 stops. Do you find this to be the case in general? I'm including
max black and paper white in the range as steps (wanted to clarify because some
don't include paper white).
Off to work, though I'd love to have this convo
instead...
Chris
__________________
----- Original Message -----
Sent: Monday, December 08, 2008 10:55
PM
Subject: Extending gum range and the tone
reversal.
All
A few weeks ago I was printing gum from a negative
that was way too dense. It was not my nagative, so I really could not do
anything with it. When I printed a thalo blue layer I noticed a tone reversal
and a heavy stain in the highlights. I typically do not encounter either as my
gum negatives are not that dense. This was an opportunity to learn so I
printed some step tablet tests and determined that indeed a little exposure
was needed or else a "tone reversal" or heavy stain resulted in the test
prints.
That prompted me to add some 'flash' exposure, no negative in my
UV box. I am posting a test printed with thalo green, one of the most staining
pigments. I had a test strip with thalo blue and indanthrone blue, but can't
find them now.
On the test strip there are 1, 1:30 and 2 min exposures.
You can easily see the tone reversal on the 1 min exposure where the number 21
is much lighter then say 8. I also posted RGB readings to illustrate the
stain. I wish I had done a 4 minute exposure as well, next time I
suppose.
The center 3 strips are 1:30 second exposure with 2, 5 and 10
second post flash with no negative. Steps 1-7 are visible on the print, maybe
not quite on the scan. There is also very little stain and no tone reversal.
this is a remarkable density range for gum. This was all printed and developed
on one piece of paper to have the development constant.
I have been
printing with a flash for a while now. This really opens up the
highlights, but requires somewhat denser negatives than typical gum.
For
those ready to experiment I would suggest using step tablet and not existing
negatives to test this idea.
Always something new and exciting
with gum.
Marek
just one picture
http://picasaweb.google.com/marekmatusz1/ExtendedGumRange?authkey=AKZxcCQlqts#5277658299253953138
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