Re: haunted GUM (i surrender)

[phritz phantom <phritz-phantom@web.de>]

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/