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Re: [BKARTS] Bleaching Paper


Here's one of the earliest publications about this technique.
There are some later papers in the Book & Paper/AIC proceedings,
but this was the first.  I think.


>Please excuse any cross postings.
>Does anyone have any experience using an UV-light to bleach paper?
>Frank Lehmann
>Lehmann Bindery

Papers Delivered to the Book & Paper Group Session
at the 9th Annual Meeting of the AIC
Philadelphia, PA
May 27 - 31, 1981



This is a general conclusion of the experimental results obtained by the
joint Project of Keiko M. Keyes and Thomas J Branchick (Cooperstown Intern,
Williamstown Regional Art Conservation Lab., Inc.) with the supervision of
Dr F. Christopher Tahk. The entire body of data and statistical analysis
will be published at a later date.

The method of natural sunlight or fluorescent tube illumination used in the
bleaching of paper is the subject under investigation. The colored
components of oxidized cellulose in the presence of water become
electronically excited when struck by photons of light. In this higher
energy state, the stain molecule absorbs a photon of light and gives up its
excess energy as heat. This breaks the molecule up into smaller fragments
along with their oxidation to polar (hence water soluble) molecules. The
cellulose itself either does not absorb visible or ultraviolet light and so
is not directly attacked by it, or if it does absorb, it is more stable in
the electronically excited state than are the stain molecules.

Two paper groups, an 18th c. Dutch rag laid ledger paper and a 20th c. high
alpha cellulose wove paper were used for the experiments. Sheets were
randomly divided into controls and bleaching strips. Sheets were washed in
deionized water and then further washed in alkaline deionized water
(ammonium hydroxide final pH of 8). Both washings were 30 minutes. Two
bleach baths were under investigation, both 1" in depth over the immersed
paper samples; one bath deionized water, the other magnesium bicarbonate
solution and deionized water 1:5. The bleaching took place in white plastic
trays. The sun bleaching time, in mid-day sun, was 4 hours of exposure,
three hours recto and one hour verso. The fluorescent light bank bleaching
was carried out with two constructed banks of lights. One bank consisting
of eight ultraviolet fluorescent tubes (300-400 nm of light) the other
eight, approx. 110w power groove tubes.

A third bleach bath was employed using the power groove light bank with a
sheet of UF-3, UV filtering, plexiglas placed on top of the plastic tray.
The trays were 12" from the fluorescent tubes. Bleaching time for the light
banks was 16 hours exposure, 12 hours recto and 4 hours

Visible reflectance spectra, measured over white and black reflecting
backgrounds,were recorded from 375 to 750 nm for each control, after
washing and bleached paper samples. Fold endurance testing was performed on
the same span of samples at the Institute of Paper Chemistry, Appleton,

Both sunlight and fluorescent light bank illumination satisfactorily bleach
paper. Preferred illumination is natural sunlight or power groove light
bank in deionized water or magnesium bicarbonate solutions. Visually, the
UV tube bleached samples all had a slight bluish or cooler paper tone. The
fold endurance testing determined that the paper strength increased in the
20th c. paper after bleach baths but decreased in the 18th c. paper after
bleach baths. Full interpretation of these results are still under
consideration and will be included in the forthcoming detailed publication.

Thompson Conservation Lab.
7549 N. Fenwick
Portland, Oregon  97217

503/735-3942  (ph/fax)


"The lyfe so short; the craft so long to lerne."
Chaucer  _Parlement of Foules_ 1386

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