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pH, paper, paste, postal inks, etc.



With apologies in advance for batching replies, but I've
just returned from a few days at my cabin in Idaho, checking
on the hole in the ground which has become a one-arce pond,
holding water!  Over 8 ft. at the deepest.  This water will
power the new medieval-style papermill I plan to build about
300 ft. west of the pond.

This is my personal solution to understanding more about
why centuries old paper has survived in better condition
than so much decades old paper.  And it gets me out of the house.

Peter was correct in stating that surface pH measurements are
only indicative, not as conclusive as macerating the paper
and testing the pulp slurry.

It is also important to calibrate the instrument if you are
using a pH meter, and compensate for temperature, if you are
using a TAPPI method.

TAPPI (Technical Association of the Pulp & Paper Industry) has
published a number of standard methods for measuring pH of
paper, including the pH of fillers and pigments, which can
(and do) mask the true pH you are trying to measure.

TAPPI method T 529 pm-74 is a provisional method for surface
measurement of paper.

T 667 su-68 is the TAPPI suggested method for determining the
pH of filler and pigment slurries.

TAPPI's use of terms such as 'provisional' and 'suggested'
only indicates that these questions are complex enough that
trained paper chemists haven't resolved some fundamental
questions.

Look for a copy of B.L. Browning's book, _Analysis of Paper_

Dorothy Africa suggests adding calcium hydroxide (lime) to
paste if there is a concern about pH.  I would only add that
the lime should be stirred up in some distilled water and allowed
to settle overnight.  Then use the clear water sitting on top
of the settled lime.  Water will carry approx. 1.5% to 2% of
calcium hydroxide in a 'clear' solution; the rest is filler.

Carol Pratt asked me about fading autograph album/postal inks.

That's too large a question to answer definitively in an email,
but in general, fading inks were manufactured from coal tar dyes
in a solvent (water, alcohols, etc.) with a little glycerin and
other chemicals to help them flow from the pen, or stay wet on
a stamp pad long enough to be stamped on an envelope where they
would dry, more or less, on the paper.

Cheers,

Jack

Jack C. Thompson
Thompson Conservation Lab.
Portland, Oregon

(503)735-3942 (voice/fax)

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

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