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PORCELAIN consists mainly of a mixture of kaolin, quartz, and felspar, in proportions variable to a high extent in accordance with the purpose it is intended for. For electrical applications hard porcelain, consisting of a kaolin core immersed in felspar and quartz paste, is used exclusively. This composition, which is burnt at a very high temperature, gives a very high mechanical and elec trical resistance, as required in electrical insulators. After being crushed and ground, the quartz anddoi:10.1038/scientificamerican08031912-72supp fatcat:kzzmtcwpbjbe7j4gpuq2mwxox4