[pure-silver] Re: curled fiber edges
----- Original Message ----- From: "Bogdan Karasek" <bkarasek@xxxxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, April 23, 2008 7:05 AM
Subject: [pure-silver] Re: curled fiber edges



Hi Nicolas,
Pakasol? More details on this; looks interesting; solution to a persistent problem? 

Cheers,
Bogdan
Pakosol is a print flattening solution. Most of these are solutions of glycerin with perhaps other substances. They are humectants intended to keep the moisture content of the emulsion high. There have been questions about the effects on the longevity of images when such flatteners are used. I don't know if Pakosol is still made. Pa-Ko made processing equipment for photofinishers including large drum dryers. A treatment like Pakosol is used with heated dryers to avoid over drying and consequent brittleness of the emulsion and substrate. Any flattening process is ultimately aimed at balancing the moisture content of the emulsion versus the support. Curling of paper (or film) is due to the different rate of shrinkage of the emulsion and support at various amounts of moisture content. The emulsion side tends to shrink more than the paper so the usual curl is toward the emulsion side. Cockling or rippling near the edges is related to curl but is due to some non-uniformity in the coating. I used to have this problem especially with older Agfa papers. If its not too severe the dry mount press flattening process will cure it but, if severe, there may be damage at the edges of the print requiring trimming. I used the word frilling in my post because I couldn't think of "cockling", frilling is really something else but is similar to a very fine cockling at the edges but usually with loosening of the emulsion. This must be trimmed off. What has been missed in most of the posts is that the paper backing must be dried more than the emulsion in order to equalize the shrinkage. When using heat and mild pressure, as in a dry mount press or hand iron, the emulsion side must be protected by a moisture impermiable covering such as dry mounting releas tissue. Otherwise it will be dried out and the print will probably curl again. Also, because there is to some extent a sort of molding of the emulsion, its important to cool the ironed or pressed print under a flat weight leaving the release tissue in content with the emulsion to keep moisture from being lost. Drying on screens is one way to reduce the difference in shrinkage because, when the emulsion is in contact with the screen it can not dry out as fast as the paper support, which is in direct contact with the air. Old style screens, made of cheesecloth, are probably better than modern ones made of plastic screening, because they tend to absorb moisture from the print and hold it in the emulsion. Old time photofinishers used to treat prints in a mechanical straightener. These ran the paper across a knife-edge with the support against the knife edge to stretch the emulsion and substrate. I don't recommend these although they work. One can achieve the same thing by running a print across a sharp table edge. If the substrate is too dry it will crack and flake off. That used to happen with drum dryers when the heat was turned way up to shorten drying time. Again, I've posted a complete dry mouting procedure to this list and to a couple of usenet groups in the past, the correct flattening procedure is part of this. Its easy to do on a press and will work with a hand iron. I will repeat the thing here if requested. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx


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