[pure-silver] Re: RC to FB
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 01 Jan 2005 17:27:27 -0500 (EST)
From: "Dave Valvo" <dvalvo@xxxxxxxxxxxxxxxx>
Subject: [pure-silver] Re: RC to FB
Date: Sat, 1 Jan 2005 11:26:36 -0800
> In some circumstances plastic glazing is recommended in place of glass. In
> fact, before I knew better, I used to recommend the use of Cyro OP-3 acrylic
> sheet since it was so white and clear, is light weight and has excellent UV
> absorbing properties. It did reduce brightener degradation in the tests.
> But now I know that it is also very porous to atmospheric gases and any
> pollutant will go right through it. I changed that recommendation. So if
> you have an old Kodak print storage document with OP-3 in it ..toss it.
> Glass is better.
Poly(alkyl methacrylate) is very strong and has optical clarity far
superior to glass in visible spectrum and many remove parts of UV
irradiation. An example is Plexiglass from Rhom and Haas. Very thick
walls of huge aquarium tanks are made from this type of polymers
because glass of the same thickness would be so dense.
Glass is impermeable to practically everything of concern in this
discussion. But I think this difference matters only if you make
perfectly sealed framing. I am not sure if there is a significant
difference in total barrier properties of an ordinary framing, between
glass and plexi-type material.
Also, once the print is toned in a sulfiding toner, the print is
practically immune to sulfiding pollutants and all but most potent
environmental oxidants. I wonder if plexi is significantly inferior in
framing sulfide treated prints in ordinary framing techniques (i.e.,
without perfect sealing on the back).
> The boards are made of alpha cellulose not cotton rag. ( although
> they may have extended "artcare" into their cotton rag products by
> now.)
Can you explain the significance of this distinction in this context?
I use paper made from pure cotton to make my printing paper, because
cotton is 98.5+% alpha cellulose. I avoid wood pulps because they use
lignine removing agents, possible residue of which is known to cause
emulsion fog. Alpha cellulose content is very important for printing
paper because lower quality papers contain greater fractions of beta
and gamma cellulose, which is soluble in alkaline solutions
(insufficient wet strength). Commercial fiber based papers generally
use fibers of lower quality than the stock I use but with more
specialized sizing techniques to make them durable during wet
processing. However, I don't know much about their difference in dry
condition such as when they are used as a framing material, especially
as the backing board.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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