If you study bricks in warm climates as much as I do; we have no where near
the failure on glaze as there is above zone 7 on the freeze thaw map,
we do have the biological growth however;  my take is  there is a porosity to
almost all thin glaze exposed to Ultra Violet..
.( you remember her she danced in Vaudeville...no it was with Warhol )
so might the technical answers lay within the make up of the glaze.....Michael

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