Chalk drawings

Robert Smith <member [at] basiliscoe__fsnet__co__uk> writes

>Does anyone have experience of the conservation of chalk drawings on
>blackboards? ...

Two conservation considerations spring to mind with framing as you
suggest. The first is that you would create a sealed environment.
Within this enclosure the wood of the blackboard (and the rebate of
the frame if made of wood and not sealed) will be off gassing
organic acids.  In a sealed (or almost sealed) environment the
concentration will build up and react with the chalk (calcium
carbonate).  The other consideration is that polishing the glazing
can create a charge of static electricity that could pull chalk
particles off the surface of the blackboard.  The danger is greatest
with acrylic glazing.

These can be mitigated by:

    a)  sealing the rebate of the frame with a premium grade
        aluminium tape

    b)  adding buffered acid-free board to the inside of the package
        to absorb and neutralise acidic vapour (for example around
        the rebate where it can also act as a spacer)

    c)  increasing the space between the chalk and glazing (the
        attraction is inversely proportional to the square of the
        distance)

Another subject to consider is that glazing a black surface
accentuates reflections.  Fortunately high quality, coated,
low-reflective glasses are available to combat this.

Nicholas Burnett
Director
Museum Conservation Services Ltd
+44 1223 830373


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                  Conservation DistList Instance 22:50
                  Distributed: Tuesday, March 3, 2009
                       Message Id: cdl-22-50-006
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