Iron spots

Iron spots on and in the porcelain

Iron spots and dots are brownish deposits anchored deep in the body, which bleed outwards. They are often confused with the burn marks, but they occur in a different way. Obviously, iron spots can lie under the glaze as well as have an open-pored connection with the glaze.

This is caused by microscopic impurities in the porcelain mass caused by metallic solids (iron or iron oxide), which are normally removed from the powdered raw material by electromagnetic means before the porcelain mass can be prepared from the various earthen materials (kaolin, feldspar, quartz and water). Iron spots appear only after hard firing and cannot be removed.

Clearly visible iron spots on the upper side of the porcelain are classified as "b-grade" (second choice).