Early phenol-formaldehyde and urea-formaldehyde plastics

James Tapley <jthandbook [at] aol__com> writes

>I have acquired a badly damaged (cracks, losses) art deco Reliure
>Jotau industrial molded "Bakelite" bookbinding. While these bindings
>are always referred to as made of Bakelite I believe, based on the
>unpainted but rather colorful plastic, that they are perhaps made of
>a urea-formaldehyde  plastic. Can anyone suggest a relatively simple
>and non-destructive test for distinguishing between urea- and
>phenol-formaldehyde plastics? ...

In response to James Tapley's request for a simple test for
distinguishing between a urea and phenolic plastic bookbinding:
Scrape a ground glass slide across an inconspicuous area of the book
cover e.g. a corner or edge. This will give a line of sample on the
slide suitable for two or three spot tests  but causes minimal
damage to the artefact. (Thanks to France Remillard for this
technique). Apply a tiny drop of 5% diphenylamine solution in 90%
aqueous sulphuric acid to the sample on the slide.  (Note:  Very
concentrated acid! Refer CCI notes 17/2 Williams, "The Diphenylamine
test for cellulose nitrate" for a slightly different version of this
spot test.)

Cast phenolic resin will give a magenta pink stain, the depth of
colour will depend on the amount of sample on the slide. The test
works only on the colourful, cast phenolics, not on the heavily
filled, dark, industrial phenolics which were manufactured by a
different process. The same test will  give an instant very dark
blue stain on cellulose nitrate samples and a blue-green colour on
many other plastics including most urea and melamine formaldehydes.
However the blue-green is not diagnostic for those plastics because
it appears to be a  response to additives rather than the polymers.

Julia Fenn
Royal Ontario Museum


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                  Conservation DistList Instance 18:36
                 Distributed: Sunday, January 30, 2005
                       Message Id: cdl-18-36-019
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