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Subject: Deacidifying charcoal drawings

Deacidifying charcoal drawings

From: Siew Wah Lee <lee_siew_wah<-a>
Date: Monday, November 3, 2008
Justyna Szpila Verdavaine <justyna_szpila [at] yahoo__fr> writes

>I wonder if a contact washing with a blotter paper moistened with a
>buffer solution would be an option, or spraying? I have heard about
>the Wei T'o method but has anyone used this for art drawings? What
>were your results? Is the method commercialised in Europe?

The treatments depend a lot on the what type paper the drawing is
on, the condition of the paper support and how loose are the
charcoal particles. It is hard to say what type of treatment is
suitable without assessing the object.

If the paper is made of cotton rag, there is not a need to deacidify
after all there is not much acid content from the paper. The
charcoal drawings I come across are contemporary ones, some are on
woodpulp papers. Most people might thought that woodpulp papers need
to be deacidified, actually not always. Most of the modern woodpulp
papers sold as art materials are highly purified, neutrally sized
and alkaline. The usual acid and discoloration I have seen on them
are from bad mounting/framing or storage practices like poor quality
mounts or wooden backings in frames rather than from the woodpulp
materials. A common slight discoloration on new modern papers after
a few years is due to the degradation of the optical brighteners,
not related to whether the paper is buffered or not. Proper mounting
on alkaline ragboards and good storage environment of the drawings
will retain the alkaline buffer inside.

The only papers I deacidify are newspapers, documents and papers of
daily use. These papers are usually made of poor quality woodpulp
papers with no alkaline buffer and many contain lignin. Older ones
with alum rosin sizings. Many of such papers are acidic and
deacidification is needed for their preservation. Sprays like Wei
T'o, Bookkeeper, etc. are meant for libraries and archives to do
mass deacidification of books and documents. I do use Bookkeeper
occasionally for documents and newsprint magazines with sensitive
written media that cannot be washed, after testing beforehand that
media do not react with the alkaline. A white cast of magnesium salt
deposits was usually found on the paper support after I did the
spraying, especially when too much was applied, but it can be easily
removed with dry cleaning method.

I never use Bookkeeper on artworks as some painted media are
alkaline sensitive, the pH of the alkaline spray is on the high side
which I feel a bit too high for the works of art here. I will
caution against using such sprays on charcoal drawings, any white
deposits will be obvious and it is very difficult to do surface
clean for charcoal.

Siew Wah, Lee
Paper Conservator
Heritage Conservation Centre
National Heritage Board

                  Conservation DistList Instance 22:27
                 Distributed: Sunday, November 9, 2008
                       Message Id: cdl-22-27-004
Received on Monday, 3 November, 2008

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