Lusterware or Lustreware (American and English spelling) is a metallic pottery glaze of beautiful iridescence achieved by the metallic oxides applied over another finished glaze, usually during a third firing (overglazed).
Origin of lusterware pottery
First examples of lusterware come from the Islamic Mesopotamia, technique that was extended all over the Caliphate territories. The mass production begins during the Abbasid Caliphate, IX century, possibly due to the Islamic prohibition of the opulent luxury. Historians think that precious metal tableware was naturally substituted by beautiful lusterware pottery.
Interesting facts about Islamic lusterware
One of the greatest remaining examples of Islamic lusterware tiles is the Great Mosque of Kairouan.
Interestingly enough, Maghreb and Al-Andalus potters were famous for their perfected technique and the knowledge of a "secret" process. The only secret of high quality lusterware, just like many other pottery endeavors, is the trial and error approach and learning from experience. The third firing, being the most critical and harsh to execute needs long hours of care and can very easily go wrong. An experience of 20 years is needed to get the mastery of this artisan craft.