Transactions of the INDIAN CERAMIC SOCIETY Vol. 18 1959
PLASTER OF PARIS*
ATMA RAM AND SUDHIR SEN**
Pages : 35-54
DOI :10.1080/0371750X.1959.11011909
Abstract
Plaster of Paris is a very common material
used in the ceramic industry for making
moulds for shaping the articles. It is
obtained by heating the naturally occuring
mineral, gypsum (CaSO" 2H20) at a
suitable temperature, so that theoretically
three fourth<: of the chemically combined
water is driven out and the product approximately
becomes a hemihydrate of calcium
sulphate\ The property of plaster of Paris
to set to a hard mass, on mixing with water,
has led to its wide application in industry
and trade. During the dehydration of
gypsum for producing plaster of Paris,
several products varying from one which
just begins to show some setting tendency
to the one which has lost all setting property
(insoluble anhydrite) may be formed2
·".
The properties· of the plaster determining
its usefulness are dependent not only on tl1e
quality of the gypsum used in its preparation
but even more so on the extent and uniformity
of calcination. The amount of water
to be added to the plaster to bring the paste
to a workable consistency is determined by
the temperature of calcination and is a
factor which greatly influences its behaviour
in service4
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