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Re: Paper deacidification



Deacidification is one of those tricky areas in the business
of restoring paper/books.

Generally speaking, the paper will benefit if the acids from
manufacture and those absorbed from the environment are
neutralized (brought to a pH of 7, more or less).

Alkalization is another animal altogether (did Don Etherington
create or popularize that term?).  This means introducing an
alkaline buffer into the paper.

Sometimes, it is not a good idea to introduce a buffer (thus
bringing the pH above 7) because some inks are most stable
in a slightly acid environment, and some colored inks are
pH indicators; that is, they will change color to reflect a
change in pH.  Canary yellow can change to a very nice pink
if it is made alkaline....

Over the past few years picture framers have brought me modern
prints which have been permanently 'stained' where they placed
alkaline, buffered hinges.  The alkali migrated through the paper
and changed the color of the ink on the image side.

Some people are very enthusiastic about deacidifying/buffering
paper when they wash it and I have felt treated paper which felt
like fine sandpaper because the excess calcium/magnesium
introduced into the paper migrated to the top surface as the
solvent (water or non-aqueous) evaporated, carrying some buffering
agent along for the ride.

A sheet of paper, newly introduced to the world, is exposed to
acidic and alkaline vapors - both of which are absorbed by paper,
because it is such a good filter.

Over time, these acid & alkaline particles meet on their strolls
along cellulose fibers and they wage war.  Both are destroyed, and
from their ashes salts are created.  Salts react to changes in relative
humidity (%RH). When the humidity is high, they go water skiing; when
it is dry, they hunker down in front of the stove, praying for rain.

Meanwhile, acid and alkaline vapors continue to be absorbed and the
wars continue.

Some of these 'dry' salts hunker down (crystalize) in neighborhoods
where cellulose fibers cross and that can create mechanical problems not
unlike throwing sand into a finely oiled machine.

Acids are absorbed by cellulose fibers and, through osmosis, they suck
moisture from the lumens (centers) of the fibers, thus making them
brittle; alkalies are absorbed and they soften the fiber walls, swelling
them up until they burst.

The end result of all this chemical activity is that the cellulose fibers
lose strength.

When we wash paper part of what comes out is broken cellulose and salts
created when acids and alkalies combined and canceled each other out.

If we wash in a slightly acid solution, many alkalies are neutralized
and are tossed out with the wash water; if in an alkaline solution, then
many acids go away; both in the form of salts.

If the paper is deacidified & alkalized (buffered) with a non-aqueous
system (and there are times when that is appropriate) then no salts
are washed away and a very large reservoir for the creation of additional
salts is created, with the attendant potential for salt (mechanical) damage.

The rambling explanation above is by way of getting to what I prefer to do
in the lab with paper which can be washed.

First, I soak it in slightly acid cold water (approx. 5.5 - 6.5 pH); then
I lay the paper on a drying rack (on a support) while changing the water;
the next bath is warmer (about body temperature) and contains a little
ammonium hydroxide (ammonia; I use reagent grade ammonia from a chemical
supply house, but non-sudsing - non-perfumed household ammonia may work
as well) and raise the pH to between 7.5 - 8.0 (above that and I begin
worrying about color change; if the ink is all black I don't worry so
much; but modern black ink may be based on soybean oil and solvents, not
carbon black and linseed oil - so, I don't worry 'much' but I do test).

Depending on how much the water discolors during this bath I may do
a third or fourth bath.

In the end, the paper is set out to dry. Without buffering, unless the
client demands this additional treatment.  The ammonia will evaporate
in a short time.

My reason is this: the paper is now as strong (without additional sizing)
as it is ever likely to be and as close to neutral as this treatment
will allow.  To size, or re-size is a separate issue.

It will continue absorbing acids and alkalies from the atmoshpere, but
I have not created a mechanical reservoir to hasten the degradation which
will happen in due course and with any luck, my treatment has put that
day off a good while.

Jack

Jack C. Thompson
Thompson Conservation Lab.
7549 N. Fenwick
Portland, Oregon  97217
USA

(503)735-3942 (voice/fax)

http://www.teleport.com/~tcl

"The lyf so short; the craft so long to lerne"
Chaucer, <The Parlement of Foules> 1386 A.D.

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