GLAZING OF UNDERFIRED COLORS
Even though every precaution known to the art has been observed, the artist will be puzzled in taking from the kiln pieces that have been fired in a way anything but satisfactory or as he expected. It is frequently the case that his best pieces are underfired. Knowing the danger of over firing, he is liable to make this mistake. Should this happen, it is not well to refire china without going over the work with a thin coat of color. This should be fired at the same heat as would be used in the ordinary glaze. In case you do not need to go over the whole decoration, the fired colors could be covered lightly with a coat of enamel oil, or mixing oil and turpentine. Let this coat dry, padding it well, after which dust it with white flux or ivory glaze. The desired glaze will be produced by the powder adhering to the oil. Fire again with ordinary heat.
A glaze cannot be produced on underfired china by using a coat of lustre, but instead it will be found that this china will absorb the glazy substance of the lustre. This has a tendency to change the colors and produces a frosted effect.
Sometimes white lustre will retain its glaze over a lightly fired tint, but we suggest that the decoration be retouched after the colors are very dry, and powder it with ivory glaze. Pure glazes or fluxes mixed with oil should never be applied over the unglazed decoration—as it will invariably destroy the colors. A rough surface can be improved by rubbing it gently with very fine emery paper.
You will find that a good oil for glazing is made by the turpentine in the cup, that you use for washing brushes. The glazy qualities are produced by the fluxes of the colors. Great care should be taken to see that this oil is clean. After giving the underfired decoration a light wash, pat well. Fire in the usual way after it is thoroughly dry, and a very satisfactory glaze will be obtained.