Magic slate

Erin Thompson <erine_thompson [at] yahoo__com> writes

>At our museum, we recently acquired a "magic" or "fun" slate from
>1961. This object consists of a dark, waxy layer underneath a
>plastic layer. You would write with a plastic stylus on the top
>layer and then lift it to erase the writing.
>
>On our piece, the bottom layer is dried and cracking, and the
>plastic layer has become warped.  Has anyone worked with a material
>like this before?  Can anyone offer any suggestions to stabilize
>this piece so that it does not become more damaged?  Any housing
>recommendations? I can also provide images of the item in question
>if needed.

Based on the description of the warping, it is possible that the
translucent layer is a deteriorating opacified cellulose acetate
film. The shrinkage of the bottom drawing layer if actually made up
of beeswax and/or paraffin as proposed in the current patent that
you linked to, might be weighed in on by other experts in that
material. If indeed you can characterize it as wax, you might
address the cracking and fills as one would approach consolidating a
wax seal (see: Lapkin et al, Waxing Scientific: Exploring New
Options for Wax Seal Consolidation. The Book and Paper Group Annual
21 (2002)).

As for housing, if it does contain cellulose acetate, you don't want
to concentrate offgassing fumes in a tight enclosure such as a
plastic sleeve. You may wish to create a sink mat or a box of mat or
corrugated board to protect the edges and provide handling
apparatus, and protect it from dust with a cover, so that it can
release acetic acid vapors instead of concentrating them. These
vapors can affect objects nearby, so use caution when storing with
other items, organic or inorganic. Low-temperature storage is
another option, to reduce rate of degradation.

You may be interested, philosophically, in a blog I wrote on
preservation of objects meant for ephemeral writing:

    <URL:http://siarchives.si.edu/blog/take-picture-it-will-last-longer>

Do look at the comments in which an interesting discussion follows.
Due to my interest in related items (plastics, including acetate
overlays, in books and archives), I'm curious to know what our
collections over at the National Museum of American History may hold
for comparison. You are welcome to send images to my attention at my
work address lockshinn<-at->si<.>edu further discussion.


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                  Conservation DistList Instance 26:50
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