U of S | Mailing List Archive | alt-photo-process-l | mounting board, alkalinity, etc. (was Re: pt/pd mounting)

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

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

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.