• Soda, Lime and Sand


    Glass, the initial components of the mixture of which are quartz sand, soda, and lime, is called sodium-calcium. This glass is about 90% of the glass produced in the world. When founding, sodium carbonate, and calcium carbonate decompose in accordance with the equations:
    Na2CO3 → Na2O + CO2
    CaCO3 → Cađ× + CO2
    As a result, the glass contains oxides SiO2, Na2O, and CaO. They form complex compounds - silicates, which are the sodium and calcium salts of silicic acid.

    Glass Founding
    Glass Founding
    Soda is a raw material, which is relatively expensive and has a huge demand from various sectors of the economy. Therefore, the natural mineral Na2SO4 is also used as a source of Na2O during glass founding. However, in this case, glass founding requires higher temperatures. In addition, coal must be injected into the charge for sulfur reduction.


    Glass from Mesopotamia and Asia Minor
    Glass from Mesopotamia and Asia Minor
     When glass is melted, the alkali metal oxide is first melted, after which grains of quartz and limestone begin to dissolve in this melt, entering into chemical interaction. Therefore, the more alkali metal oxides are in glass, the lower is the temperature of its melting. In ancient Egypt, when the technique of obtaining high temperatures was imperfect, recipes with a high content of oxides of alkali metals (up to 30%) and low content of lime (about 3–5%) prevailed in glassmaking. In the Hellenistic era, with the improvement of technology for producing high temperatures, the content of alkali metal oxides is reduced to 16 - 17%, and lime increases to 10%. Naturally, such glasses have become more resistant to water. Currently, glass founding is realized at a temperature of 1400 -1500°C for several hours.

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