Oxidizing flame - mixture of gases contains more oxygen than fuel
gas ( whatever that may be ), the flame tip is bright blue and sharp.
Since excess of oxygen insures complete combustion of fuel gas, the
temperature is very high.
Neutral flame - mixture contains equal amounts of oxygen and fuel
gas. the flame still sharp but instead of needlepoint it is somewhat
roundish. Color is pale-blue.
there is no excess of either components. The most useful
configuration, especially for the beginner. Reducing flame - excess
of fuel gas in the mixture. Flame is very soft, with yellow tip.
Almost a must for working with silver due to the high thermal
conductivity of silver.
the name comes from the class of chemical reactions known as
"reductions". To understand this consider the following: Gold is
alloyed with silver and copper to produce commercial alloy. when we
heat the gold, the copper oxidizes and created copper oxide on the
surface, the black discoloration. Formula CuO. If there is excess of
fuel gas in the mixture, the product of burning such a mixture is
pure carbon, black soot. When carbon, chemical symbol C. combines
with copper oxide, CuO, at the presence of high temperature the
result of the reaction is carbon dioxide with some carbon monoxide,
depending on how much free oxygen is available and pure copper.
2CuO + C = CO2 + 2Cu
In words, the copper oxide was reduced to metallic copper, therefore
is the name "reducing".