Richard Mahaffey on mon 29 may 06
David Beumee wrote:
Carbon monoxide is a very tiny molecule, and has no trouble stealing oxygen from the glaze or clay and replacing it with carbon
So David, you say that Carbon Monoxide takes an oxygen atom and leaves a carbon atom resulting in O2 and oxygen molecule? I am not sure that you are correct.
Please forgive me if I am using the incorrect terminology and BE NICE as my last chemistry class was in 1968! and it is Memorial day - school is closed so I can not ask the resident chemist in the faculty building where we both have offices - I will try to remember to check with him tomorrow. (I don't want to open the chem text books that I have because it induces flashbacks - and headaches;) )
I think the carbon has a higher affinity for oxygen than do the metallic oxides and when enough energy is present (read heat) the carbon monoxide molecule takes an oxygen and turns to carbon dioxide molecule.
Metals like copper and silver have lots of oxygen states (as I recall these are ions with varying numbers of oxygen atoms missing so the resulting molecule has protons that have no matching electrons which went away with the oxygen atoms) that they can exist at in a glass matrix the higher the atomic number of the metal the more oxygen states are available for use in coloring glazes.
As an aside Iron has a stronger affinity for Oxygen than does copper, tin is the same as well so it is fairly common to find both Iron and Tin in a copper red glaze. The function of the tin and the iron is to grab up any stray oxygens floating around and keep them away from the copper, thereby adding some insurance of a red glaze result.
Seems to me that perhaps Parmalee's _Ceramic Glazes_ had a chart showing the relative affinity for Oxygen of various glaze constituents.
YRCMV - Your Reduction Chemistry May Vary,