A brown colored glaze, high-fired rust brown speckled glaze.
It appears as if the iron rust effect results from an iron rich glaze being allowed to cool down slowly, which leads to iron - 'oil' - spots poling on the surface.
A similar glaze is the tea dust glaze that seems to be created in a similar way, but is maybe just fired up to a slightly lower temperature, before it is allowed to cool down slowly.
See also: Tea dust
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