Consolidating chalkboard

Susan Russick <susan-russick<-a t->northwestern< . >edu> writes

>We are anticipating the accession of a green colored chalkboard
>(about 4 feet x 6 feet) featuring a multitude of economics equations
>in chalk by a Nobel laureate professor.  We would like to
>consolidate the chalk to retain the writing.  ...

I would like to suggest that you try an atomized spray application
of funori as a fixative to consolidate the chalk powder on the chalk
board you are about to accession.  Funori is one of the traditional
restoration materials of Japan.  It is used as an adhesive,
consolidant and fixative.  Funori is the generic name that includes
several kinds of red seaweed from which a unique polysaccharide
starch is extracted.  The extract, as a clear liquid applied with an
airbrush, has the characteristics of drying to a reasonably durable
matte finish, leaving no tide lines on absorbent materials (this may
not be relevant here as the surface of a chalk board may not absorb
the water carrier and therefore will not mobilize the salts, the
coastal drying of which results in tide lines) and appears to retard
fungal growth in material to which it is applied.  The starch makes
a protective layer where applied. It can be renewed by subsequent
applications.  There is a very slight saturation of colors.  It is
utterly non-toxic.  If possible, I would suggest the chalk board be
laid out horizontally to minimize the possibility of runs or drips.
I doubt if this application or any other direct conservation
treatment of the chalk on this substrate would be reversible.

We have used funori successfully in a historic house museum setting
to consolidate extremely friable tempera paint that had lost its gum
Arabic binders.  The tempera had been applied by a decorative
painter over oil-painted ceiling and upper wall plaster in the late
19C and had deteriorated to the point of being little more than a
colorful powder residue on the surface.  The thought of chalk on a
chalkboard reminded me of our situation.

Funori misted across the surface in several light coats dried matte,
made the surface strong enough so that feather dusters could be used
in house-keeping, and has been stable in the ordinary fluctuating RH
of a historic house museum for three years now.  The areas treated
cannot be distinguished in sheen or saturation from adjacent areas
of background painting that did not get the funori application.

Obviously, it would be important to try a few locations
experimentally.  In a school setting, green chalkboard and white
chalk for trials will be easy to find.  It can all be washed off
with water.  Chalk for classroom use hasn't changed over the years
and the green boards will have been standard issue.

Historic Plaster Conservation Services produces a very pure form of
funori from raw, never -chemically bleached, seaweed, which we
import directly from harvesters in Japan.  Our TRI-Funori is
described on various pages and a video at

    <URL:http://www.historicplaster.com>

Samples for testing are available to conservators on written
request.  For those wishing to make their own, funori in a hydrogen
peroxide bleached mat format is available from various conservation
supply houses.  Lascaux, the art supply manufacturer produces a
dehydrated--add water and stir--product called Jun-Funori.

Rod Stewart
Historic Plaster Conservation Services Limited
26 Barrett Street
Port Hope
Ontario L1A1M7
905-885-8764


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                  Conservation DistList Instance 28:2
                   Distributed: Monday, June 16, 2014
                        Message Id: cdl-28-2-007
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