mounting board, alkalinity, etc. (was Re: pt/pd mounting)
From: Gawain Weaver <gawain.weaver@gmail.com> Subject: RE: pt/pd mounting Date: Sat, 09 Sep 2006 14:13:14 -0400 > There is no definitive list of which photographic processes are most > suited to unbuffered enclosure materials because there is no > evidence that buffered enclosures are harmful. [...] I agree with your analysis and discussion here. > There is some concern that in a disaster involving water, the alkali > reserve from the enclosure could raise the pH of the water in which > a print is immersed. Based on such considerations, some have chosen > to "play it safe" and use unbuffered enclosure materials for > cyanotypes, and less frequently, for other processes as well. One question is that, whether the water damage to the materials freshly mounted on acid-free and alkaline buffered boards are significantly different. Such a question could be answered by testing. Did anyone run such a test? Another question is that, will the above conclusion change as the mounting board is aged. Of course, the paper adsorbs acid gasses from the environment and it also generates acid by itself, and these factors will eat up the alkaline reserve over time. From: Liam Lawless <lawless@bulldoghome.com> Subject: RE: pt/pd mounting Date: Sun, 10 Sep 2006 03:36:00 +0100 > But platinum is a catalyst and turns atmospheric sulphur dioxide > into sulphuric acid which causes yellowing and embrittlement of the > paper the print is on. If the catalyst action is the issue, the right way to deal with it is to apply a catalyst poison to the freshly made image before storage, so that Pt no longer acts as an active catalyst. If water is leaking, you better fix the leak rather than getting more buckets. However, it is *not* that sulfur dioxide is harmless and only sulfur trioxide is harmful. Sulfur dioxide gas IS harmful to paper and you want to minimize exposure to this gas to begin with. Also, the interaction of gasses in environment with paper (and silver image, though via different mechanisms) is greatly enhanced by humidity. Low humidity is a very important consideration for storage condition. From: Liam Lawless <lawless@bulldoghome.com> Subject: RE: pt/pd mounting > gum framing Date: Tue, 12 Sep 2006 02:39:26 +0100 > I'm certain buffered board has been shown to slow down image and paper > degradation due to acidity when print and mount are in a sealed or almost > sealed environment such as a frame (it is said that a small gap should be > left in the sealing tape to allow the frame to "breathe" and so avoid > condensation). Unless, of course, a high pH is antagonistic to the print! > > Anyway, this might be slightly off topic, but an article by Michael A. Smith > has a little bearing on this subject and will possibly be of interest to > those who are interested in these things: > > http://www.superiorarchivalmats.com/sam/Article.html The barrier property of the backing board has more to do with its material and its gas permeability than alkaline buffering. If the backing board is made from the same material, the barrier property will increase with the density and thickness. Anyone who use Artcare board knows that it is very much heavier and harder than boards from other manufacturers. This is significant. Due to this hard, dense board, it's a great PITA to cut a window if used as a matte window. (I use Alpharag Artcare 8-ply board and I absolutely hate this board when cutting it.) As you see in the above web site, dry mounting tissue is an effective barrier. If you used corrugated polyester board, or other board made from archival polymer plastic with good gas barrier property, you could get similar benefit while avoiding the price of the premium board and buffering dilemma. I don't know if they claim Artcare board acts as a molecular sieve (something that mops up the pollutants in the same enclosed system---just like a desiccant mopping up moisture), but looking at test results, I think it's not very significant nor very important for framing. (It's more important for storage of acetate films, for example, where the material generates corrosive acid fume.) From: Camden Hardy <camden@hardyphotography.net> Subject: Re: pt/pd mounting > not gum related Date: Tue, 12 Sep 2006 08:16:01 -0600 (MDT) > Actually, Katherine, it is. That was my question. If you refer to the > original post, I was looking to either bust or confirm the myth that acid > board is good for pt/pd prints. The real question is whether the catalyst action of Pt significantly changes with the paper pH. One thing you should notice is that, the terms "acid" and "acid-free" in paper world don't just mean whether "pH less than 7" or not. It's more than that. "Acid paper" refers to paper that is sized with alum-rosin or other strongly acidic sizing material. The term "acid-free" means that the paper is not sized with these acidic material. That's that. In any case, it makes no sense to use "acid paper." It is a simple matter to make an acid paper other than above. I can easily take an acid-free paper and incorporate suitable weak organic acid to it, to make a paper that is acidic but not as damaging as "acid paper." I'll call this low-pH paper to distinguish from customary definition of "acid paper." Acid in paper limits the life of the material. There are some sources of acids in paper: sizing material (acid paper), spontaneously generated acid, and acid from environment. The first factor is far larger than the others and therefore acid paper is not used for anything important. In the case of Pt image, the picture changes a bit. The sources of acid are: (1) sulfuric acid from sulfur dioxide gas and platinum's catalyst action; (2) spontaneously generated acid; and (3) acid from environment, other than that generated by said catalyst action. The only story that would make sense to me to justify low-pH paper is when: the (1) is the largest source of acid in Pt prints, and the amont of acid generated by the mechanism (1) can be reduced by bringing the paper acidic. However, if this is the case, the paper substrate for the image would have greater impact than mounting board. Again, the right approach to this problem is to investigate a chemical means to poison platinum's catalyst action and incorporate this poison in freshly made prints. Another important factor is to ensure good storage condition, free of acid gases, oxidative gases, high humidity and other harmful factors. Finally, acid-free is only one of many considerations for paper materials to be used for archival purposes. The paper must be mostly made from alpha-cellulose, free of lignin, reducible sulfur compounds, sources peroxide, etc. that can damage the paper itself or images. Another consideration is adhesives and other pieces that are used for framing or in the same stored container. Non-archival masking tape, for example, is a VERY bad choice. Incidentally, high quality cotton rag paper that has very good wet strength is usually very high in alpha-cellulose and practically free of lignin. From: Loris Medici <mail@loris.medici.name> Subject: RE: pt/pd mounting Date: Tue, 12 Sep 2006 00:11:59 +0300 > AFAIK, polyurethane wood finish (like Hydrocote) is impermeable to air and > water. If one coats both the front and the back of the print with > polyurethane that should protect the print very successfully (at least in > theory). I remember Ryuji had offered me his time by doing a peroxide > fading(?) test if I send him a couple of samples (polyurethane coated > Vandyke). Well if he's still interested I'm willing to send him few samples > (one coated on the front only, the other both sides and an uncoated control > strip)... Peroxide fuming test (which I can do if interest remains) can only tell you if the treatment gives greater resistance to oxidative attacks from peroxide gas in the environment. The results may be reasonably stretched to other moderately (but not very) strong oxidizing gas. However, the issues raised in this thread has more specific connection to sulfur dioxide and Pt as an oxidation catalyst, and my test won't offer any insight as to efficacy of polyurethane treatment. For silver images, several months ago, I developed a clear, weakly alkaline, nontoning antioxidant final rinse solution that gives protection to silver image. I made it for silver-gelatin (because that's what I do) but I'd be happy to test if the treatment is applicable to VDB or Kallitype.
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