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CERAMIC CHEMISTRY. The most difficult colours to obtain in pottery are the pinks and reds. No metallic oxides by themselves will give either colour ; ferric oxide, which comes nearest to red, has always a shade of brown or yellow in its effects. At Sevres they obtain a coral red by firing 28 parts of lead chromate with 75 of a flux made of 85 of minium and 15 of flint. Otsuki gives the following analysis of a blood- red Chinese glaze : SiO 2 59.6, SnO 0.32, CuO 1.2, PbO 8.2, Fe 2 O, 1.4, Al a O 3 8.4, CaO 11.1, MgO 1.7, K 2 O 2.74, Na.O 5.27, MnO trace. To produce purple, carmine, and pink, gold is used at low temperatures. Stannic ammonium chloride (pink salt) is added to dilute gold chloride solution to obtain a purple, and this may be rendered deeper in colour by adding stannous chloride. Gold-purple was formerly supposed to have the formula Sn0 2 , 2 Au, but modern thought regards it as a mixture of colloidal gold and colloidal stannic acid in different proportions. For these colours Heubach suggested a flux composed of : PbO . 65-0 . 8, Na 2 0.2-0.25, K 2 0-0.12, Si0 2 0.5-1.0, B 2 O 3 0.4-0.5. To prevent the colours turning violet a small percentage of silver carbonate or chloride is added. The ware is fired in an oxidising atmosphere at 800 C. For higher fire chromium-tin stains are used either in glaze or underglaze. Heubach gives the following formulae for the stains them- selves :