The most common method for dealing with cuprous oxide (Cu2O), once it is
found, is to try to grind past it. Abrasive grinding wheels and compounds are
used to remove enough metal in hopes that the firescale is not that deep. This
leads to removal of precious metal, loss of detail and wasted time. If the firescale
is on a detailed part, it may not be in an area that can be worked. In this case, a
decision would have to be made to live with the discoloration or scrap the part
and start over.
Electrostripping can be used to remove all the metal from the surface layers
quickly. This takes place when the sterling piece is used as an anode in an
electrolytic tank. Since silver is being lost as well as the copper and copper oxide,
this adds to the amount of metal lost in processing. Also, as the current density
is greatest at the sharper edges, detail can be quickly lost. An advanced form of
electro-polishing that does not lose the edge detail has been discussed by both
Robinson and Verdooren in recent Santa Fe Symposia. This system would require
removing all of the material from the total surface to remove the firescale.9, 10
If removal of the cuprous oxide (Cu2O) is not feasible, it can be hidden.
Electroplating with a fine silver layer after final polishing will give a bright clean
look to the piece. On items that are worn, this may not be feasible as the plating
will wear off after time. The extra cost of fine silver plating is also not a desired
solution.5
Reducing atmospheres were already discussed in the firescale prevention section
above. A true reducing atmosphere will not only remove any free oxygen from the
system, it will also break apart metal oxides into the pure metal and oxygen. The
reduction gases discussed here will be hydrogen and carbon monoxide.