Copper can be produced from many different raw materials, the main being black tenorite (CuO), deep red cuprite (Cu2O), bright green malachite (CuCO3.Cu(OH)2), and bright blue azurite (2CuCO3.Cu(OH)2). -Under normal oxidizing conditions the CuO molecule remains unchanged and produces clear green colors in oxidation glazes. The shade of copper greens can vary with firing rate and soaking changes. The best colors are generally obtained with fast firing and little soaking. CaO is unlikely to affect the color of copper in a glaze. -Copper is well-known for its ability to produce blood-red and fire-red colors in reduction atmosphere firings where it is altered to Cu2O (see Cu2O). Purple copper reduction glazes are the result of a mixture of copper in its green oxidized and red reduced forms. This effect appears most frequently in high lime glazes or where early stages of firing are oxidizing or latter stages are light or neutral. -Copper is a strong flux and even 2% can considerably increase the melt fluidity of a glaze. -Generally additions of copper to a glaze will reduce its thermal expansion. However there is some doubt about the truth of this, it needs to be confirmed. -Crystalline glazes can be attractive when done with copper. -Copper and titanium can produce beautiful blotching and specking effects. -Pure copper metal filings can make an extremely potent specking material (and contaminant, depending on your viewpoint) in reduction firing for both bodies and glazes. -Leaching: When added to low lead solubility glazes copper can cause the solubility of the lead to be greatly increased. Copper is well known for this effect in glazes at other temperatures also. Do a leaching test to be sure. -In the enameling industry, copper is used in combination with small quantities of cobalt, manganese, or nickel in making black where the black is produced in the smelter.Copper Oxide (Black cupric oxide - CuO) COPPER CARBONATE. Black cupric oxide can be soluble in fruit juices & should not be used on ware intended for food or beverages. CAS#7440-50-8
