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Re: Paper deacidification



Jack

Thank you for taking the time to write such a clear, detailed and user
friendly analysis of the how and whys of the deacidification process.  I
love reading about the various individual experiments in this area, but
truly appreciate concise chemical parameters such as those you have
provided.

Jim Ann Howard




--- Original Message -----
From: Jack C Thompson <tcl@TELEPORT.COM>
To: <BOOK_ARTS-L@LISTSERV.SYR.EDU>
Sent: Sunday, October 01, 2000 4:43 AM
Subject: 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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      For subscription information, the Archive, and other related
            resources and links go to the Book_Arts-L FAQ at:
                      <http://www.philobiblon.com>
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