Halo effect
A phenomena seen on the clear porcelain glaze surface surrounding in particular the early blue enamels of the Kangxi period. The halo (iridescence) is visible especially when Kangxi porcelain is held at certain angles to the light, and is regarded as a mark of authenticity in wares from the Kangxi period.
This halo is likely to have been caused by the use of salpeter as a flux (melting substance) in particularly the blue enamel to lower its melting point and to make it possible to fire the blue together with the other enamels in one firing.
See also: Iridescence
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