Re: possible answer to archivalness comparison between carbon gum andpt/pd
From: Gawain Weaver <gawain.weaver@gmail.com> Subject: Re: possible answer to archivalness comparison between carbon gum and pt/pd Date: Sat, 01 Mar 2008 08:04:31 -0500 > however, as was pointed out in the last archival go-around, > archivalness is not a useful measure when speaking of the > permanence qualities of various processes, and I don't think > there can be any one correct answer to the question I agree. I think the way I said is that "archivalness" is not a single variable measure that you can compare among different processes or materials. This is because each process or material has its own archival weakness that may be different from those of other processes. It is a lot more constructive to know the weakness of your process, and then how best to protect the work from it. I have no experience with carbon prints, but I can say something about gelatin. Gelatin becomes very brittle and easy to crack when kept in extremely dry condition, and particularly dry and warm condition. If the gelatin is loaded with pigment or other matters, the gelatin may be even easier to crack. Gelatin is not a single substance. It is a processed animal product that comes in a hugely wide range of grades and qualities, and only some of them are characterized (such as average molecular weight, bloom strength, hide/bone gelatin, acid/lime extraction, extraction number, etc.) It is easily conceivable that some of these variables are highly correlated with the tendency of the gelatin to crack. Another thing about gelatin is that you can use a small amount of gelatin plasticizer, such as dextran, sorbitol, poly(vinyl pyrrolidone) and its copolymers, cellulose derivatives, starch derivatives, glycols, glycerols, etc. to prevent gelatin from becoming brittle in dry conditions. Some of these are used for silver gelatin material in the past and/or present, that is, there is no other harm if used correctly. In silver gelatin materials, selection of suitable plasticizer is a rather tricky business, since many of these things make gelatin film swell excessively in processing chemicals, and also because some of these plasticizers are removed by wet processing thereby losing the needed effect when prints are stored. However, selecting a plasticizer for processes where gelatin layer is never subjected to wet processing is much easier. Residual iron in paper can be very harmful. Iron is a very effective catalyst to generate hydroxyl radical, which is a very strong oxidizing agent and it is known to attack cellulose. If I used iron-based processes, I would definitely test for complete removal of iron, and think about ways to ensure complete removal of it from the paper, or at least ways to inactivate iron if complete removal is difficult. -- Ryuji Suzuki "Make something religious and people don't have to deal with it, they can say it's irrelevant." (Bob Dylan, Biograph booklet, 1985)
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