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Glass Making a. First, sand, soda, limestone, dolomite, and feldspar, are mixed in the mixer. b. Then, they are transfered to the tank furnace. c. There they are heated to a temperature of about 1500 degree celcius. d. When the glass is liquid, the temperature is reduced to about 900 degree celcius. e. Arsenic and manganese dioxide are added. f. Discoloration is removed. g. Then, the liquid is moulded in the required shape. h. It is cooled slowly. i. Cracking is stopped.