The thermal sensitivity of glasses

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In the production of f i r s t -g rade chinaware and decorat ive objects use is made of so-ca l led sulphide-zinc glass (developed by E.A. Ivanova and A.A. KivTyanen) which is c lassed as a hea t -sens i t ive glass. Heat sensi t ivi ty shows up on the glass ' react ion to rapid c o o l i n g i n the crysta l l iza t ion of the cooled areas or,, conversely', in the absence of any crystal l izat ion. Depending on the manufactur ing method, we can produce different patterns onthe par ts during the p rocess of hot molding. The rate of formation of the pat terns and their degree of c lar i ty a re determined by the ability of the glass to c rys ta l l i ze as a function of the change of temperature. If cer ta in a reas of hot glass cooled to a considerable degree (for example by cold metal), after reheating they exhibit crystal l izat ion, whereas the remaining areas remain translucent. The opposite effect may also occur. Thus we can produce the imprint of a metal stencil on the glass, and then make a par t with a c rys ta l l ized pattern after corresponding shaping. The essence of the effect underlying the p rocess in question is that the tempera ture at which crys ta l l iza t ion begins and the rate of it depend on the thermal p reh i s to ry of the specimen. The t emper ature range over which there is crys ta l l iza t ion and the nature of the crysta l l iza t ion depend on whether the glass is cooled down or heated up to the tempera ture range that is to be studied. At the r e s e a r c h labora tory of the Decorat ive Glass Plant a study is being made of the thermal sensi t ivi ty of different glasses. It has been found that this sensit ivity is not a proper ty inherent in any par t i cu la r group of composit ions alone. Any group with cer tain components may prove thermal ly sensit ive to different degrees.