Re: haunted GUM (i surrender)
I'm sorry, it's not fair to laugh when someone's frutrated, but your
comment at the end, "gum is the devil" made me laugh out loud. I was
laughing with you, not at you, if that helps.
I had meant to look this all over again and get back to you hopefully
with more ideas, but what with one thing and another I haven't done
it. The main problem is that tonal inversion with gum is one of
those very little-understood things that I was hoping this thread
would shed some new light on, both for you and for all of us.
What makes it hardest to understand, of course, is that you weren't
getting the inversion with the same materials before (and same
pigment concentration, right?) If that's so, that leaves
environmental conditions. How about ambient humidity, has it changed
drastically in the interim?
I don't think the drying with fan or without, or the mixing, should
have any influence on this.
On Oct 8, 2009, at 5:44 PM, phritz phantom wrote:
thanks for all the answers and tips. but still no success.
chris,
the thing with acidity sounds interesting. i will keep my eyes
peeled for anything that could influence the ph-value.
i do have some glutaraldehyde. i bought a bottle of rollei hardener
for photo emulsions a while ago. then i did some reading on -
aldehydes... i only have one work room and a bathroom for anything
photographic, no lab or studio. no balcony or garden. it made me
way too nervous with all the outgassing, so i ordered the chrom
alum. probably not healthy either, but at least it stays put.
but i will keep it in mind as a last resort.
did someone say mackie lines? got 'em.
http://i31.photobucket.com/albums/c367/phritz/mackie.jpg
i'm pretty much at my wits end (not that this was a long way....) i
will give it a break now until next week or so, otherwise i'd start
accusing people of putting something in my tap water ... wait! i
used distilled. not even that i can do.
so far i've checked the dichromate, used different pigments, fresh
gum, different papers (sized, unsized and gesso). checked for
contaminated brushes, was extra carefully about unwanted exposure
to light....all either show the same results as i've shown before
or don't clear at all. only one was a little better, a strip with
pot-di, fresh gum and lamp black: the did clear and showed minimal
tonal inversion, but still had significant stain (about a zone 5)
in the unexposed areas.
i know this must sound unbelievable, but the same material printed
fine for me one or two months ago. i don't say it was perfect or
absolutely stain free (i'm pretty impatient and quickly start with
the brush and flowing water while developing). the test sheet i
posted earlier, was the same paper, the same size, lamp black and
it was absolutley not tampered with. it shows no tonal inversion
(even at 20 seconds) and no stain (except a slight yellowing from
the dichromate). most times the emulsion was off rather too quickly
than too late.
the only two possibilities left that i can think of are
a) i now dry direclty in front of a (cold) fan. before that i've
hung the papers with no fan.
b) i mix the emulsion a little differently. before i'd put the
pigment powder, the gum and the dichromate into the mixing bowl and
mix it with a little milk frothing propeller for a few seconds. now
i put the pigment and the gum into the bowl, mix with a brush until
it looks fine, then add dichromate, little more stirring, then coat.
but i can't really see those making a difference.
i will now size some paper, which will take one or two days to
harden. i will then make some more tries with sized paper.
gum is the devil
regards
phritz
Christina Z. Anderson schrieb:
Phritz,
I am so out of the loop on this one, having gotten to read all of
the posts yet except Marek's, Tom Sobota's, and your recent one.
So I really apologize if I have stuck my neck out where it doesn't
belong this late in the ballgame. I am just hoping someone will
come up with a reason for your quandary so I'll share what my
experience was with tonal inversion.
I have gotten tonal inversion when I was doing experiments with
lemon juice, making the mix more acid. I would suggest mixing up
completely fresh gum from powder, using it right away, and in
place of water use pure lemon juice in your mix, either with dry
dichromate or dry gum, and see if you notice the acidity affecting
it in any way in comparison with one that is made with water.
Marek explained that the lemon juice actually is a reducer in the
equation, and perhaps there is some sort of reducer happening in
the layers that are less exposed.
I never use sun exposure, only UVBL and consistent at that.
Another thing--is your sizing. If at all possible, if you could
get your hands on glutaraldehyde (here come the list criticisms)
and use that as a hardener for your gelatin, that would be a good
test control to see if it is the hardener that is the issue--if I
remember you are using chrome alum? I wonder if the alum is
hardening post-sizing.
That's all my (probably unhelpful) advice for today but I do hope
you get somewhere with all the advice you have been given to date
on this issue....
Chris
PS in one workshop this summer a student got severe staining with
black, and finally we realized she was printing on the unsized
side of the paper :)
__________________
Christina Z. Anderson
http://christinaZanderson.com/
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