big ugly rings cause PIA

Bob Carnie · Mar 1, 2017

Hi Folks this is gum over palladium and I am getting these rings, not the first time , had them a year ago
only thing different from workflow is the use of Citric Acid as first clearing bath and Cot320 these marks do not show up in the palladium , just when I add the second layer of gum.

Same Problem showing itself... Cot 320 palladium - PVA sizing on top - blue gum layer- If I am fast I can hit these with the brush first two minutes and they mostly go away, I have seen this problem before, and its driving me nuts.... only new thing is the Paper itself, trying no palladium on Revere and Cot320 tommorow with only gum to see if I can Isolate.

Any thoughts would be helpful,,, did I say it was driving me nuts??

ced · Mar 10, 2017

I would give a good inspection to the glass on the contact frame and then at the film from the digineg it could be something that is not easy to see but influences the passage of light during exposure.
Really only guessing here.

Bob Carnie · Mar 11, 2017

Richard.L said:
looks like 'fisheye' -- in coating the over layer is rejected by the lower coat. cause is contamination. the deposits probably (if you could see them closely) would have a depression in the center down to the lower layer.. the ring is the coating that was supposed to flow over that open area.. yep. they can be brushed in to even out...
what is the contaminant? ... small particles of "bad" chemical" or even just ambients as cigar ash etc...
old pipes may put small rust onto surface..
gum itself has particle possibles... etc
more filtering of the stages may eliminate..

if the paper were the defect you could see changes in surface with enough ?15x magnification.. i'd expect it to be visible with the 'metal' layer too.

Hi Richard

I have improved my shaking of the gum before coating and found that I am getting much smoother coats and no fisheyes with straight gums. I think you have a good description, I am going to do some prints next week where I print over Palladium and really concentrate on the filtering aspect you mention.
You are right if you catch them fast enough as soon as they form you can brush them out but I would rather find the culprit.

The water here can fluctuate in PH level and I am thinking this mineral content may be my problem, I am thinking a last two minute soak for the palladium after clearing in distilled water
and mix the first gum bath with distilled.

thanks

big ugly rings cause PIA

Bob Carnie

ced

Bob Carnie

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