Julie,

        Yes bricks will vitrify given high enough temperature. The temperature
at which this occurs depends entirely on their composition. Bricks made of
fireclay will withstand very high temperature, in excess of 1500 C, whereas
bricks made of clays with high alkali and iron content vitrify relatively
easily perhaps as low as 800 C.

        Another factor that controls the vitrification temperature, is the
type of heat involved. If bricks were in contact with the fuel then the
vitrification temperature can be reduced by the fluxing action of the chemical
components of the fuel, particularly the alkali elements.

        Mortars are another problem, a pure lime mortar would not vitrify but
revert to quick lime. However, the lime would have been mixed with some form of
filler so that again the composition will be the controling factor.

        Knowing the composition, one can look at the equilibrium phase diagram
that nearest approximates to the composition to get an idea of whether the
material is likely to be highly refractory or not. There are also various
formulae which give estimates of the initial melting points of material of
these sorts of compositions, unfortunately I do not have any of the references
to hand.

Chris Salter
---------------------------------------------
Materials Science-Based Archaeology Group,
Department of Materials,
Begbroke Business and Science Park,
Sandy Lane,
Yarnton,
Oxford OX5 1PF,

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