The Baryta layer acts as a barrier both comming and going, keeping the emulsion from sinking into the fiber and offering some measure of protection from contaminants which MAY be present in or on the paper fibers.
Since we are discussing paper which can be coated directly without this measure of protection, perhaps this form of protection is not really central here.
The original idea, I belive was not protection but enhancement of the image appearence, specfically, reduction of the dry down effect.
I found this initall post:
[Thomas] is ... most likely to try... a suggestion given at APIS to size the paper with albumen or collodion prior to coating to keep the "wet" look pt/pd prints have [initally] and minimize dry down.
Which is what Photo Engineer referrs or aludes to in the second line of his post.
Originally Posted by Photo Engineer
I should add that the concepts of "barrier" and "contaminants" come form silver halide gelatin systems and I personally do not know in fact their effcy (sp?) in the Pt/Pd process. I imagine they would be very similar.
Doesn't albumen yellow with age?
Or are there exceptions, and if so, what conditions are necessary to prevent it?
Thanks Ole, could not recall which paper it was. And yes the Art Classic Silver Supreme is a nice paper, and why not COT320 is also very nice for alt. process coating.
Originally Posted by Ole
Uh well, as Sandy said I always thought it was the job of the gelatin to prevent the emulsion from seeping into the paper, that is how we use it in alt printing. A perfect example is salt printing. You cannot make a good salt print unless you size the paper with gelatin or the silver emulsion will seep so much into the paper that it looks like a ghost print.
Originally Posted by Ray Rogers
Albumen wont yellow out if you treat with acetic acid and denaturate it, but depending on the the feed it might have a small yellowish color, not enough to change the color of the print tho.
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For those curious about this, many papers contain oxidants or traces of oxidants added during the manufacturing process and that are used to bleach the pulp or rag. In addition, clays are added along with other metal salts to act as binders.
Baryta is about 10 g/meter sqare along with gelatin binder, and this offers a thick barrier to prevent transfer of chemistry as Ray says above.
This is why you will find that RC papers (raw stock) tend to keep better than Baryta, and in most cases Baryta would keep better than sized, and sized better than non-sized. The barrier effect is greatest with RC, and least with plain paper.
The whiteness also is improved, as is sharpness. A print on a baryta coat is sharper than one on sized paper which is sharper than on non-sized.
Now, I'm speaking strictly from the standpoint of traditional silver halide emulsion coated papers. The generalizations are too general for all types of alternate printing, I'm sure, but IDK for a fact. I just know how silver halide emulsions tend to behave under these conditions.
Oh, and it has been shown that addenda in baryta coated print materials diffuse slowly out of the emulsion layer into the paper support beneath the baryta. That is why keeping is worse, the less the barrier effect. Chemical exchange begins to become quite significant as path length decreases.
This would probably also be seen in processing these materials. There would be fluctuations introduced by changes in the thickness of the path length and the materials present. I know of no concrete studies on this though, just some vague theories and hypotheses. However, RC and FB do behave differently during processing. This much is known and that is where some of the vague hypotheses and theories have originated regarding unsized papers.
Wanted to bring this post back to life and ask what results, if any, Jorge had in sizing with alubmen.
Let's see what I've got in the magic trash can for Mateo!
It did not work for me. Socorro is a very smooth paper and the albumen made it less smooth, so coating was a problem (uneven patches). Printing times were too long also, in the end I figure is best to just get a good negative...
Originally Posted by Jeremy Moore