In 1823, Berzelius prepared amorphous silicon by reducing potassium fluorosilicate with molten potassium metal. Burning or molten magnesium reacts violently with water. Sadoway, uses molten alloys of magnesium and antimony separated by an electrically insulating molten salt. Spherical particles, like those produced by atomizing molten metal, are undesirable. Aluminium is produced by electrolytic reduction of aluminium oxide dissolved in molten cryolite. Calcium nitrate can be used as a part of molten salt mixtures. The oxidation state +5 can be produced by dissolving manganese dioxide in molten sodium nitrite. Lead-coated mirrors were very thin to prevent cracking by the heat of the molten metal. It is also produced by the combination of molten bismuth and sulfur. Solar energy can also be stored at high temperatures using molten salts. This aluminium oxide is dissolved at a temperature of about in molten cryolite. One process involves electrolysis of a molten salt. Rapid cooling of molten ZnCl gives a glass. A large cauldron was filled with water, oil, tar, tallow or molten lead. It is not affected by molten alkali.