This is a piece of traditional Mexican terra cotta with a lead bisilicate glaze. It is fired at at least 1850F. We did a leaching test on the inside, using vinegar. The entire inside surface was altered to the point it appeared the glaze had dissolved away! Then that vinegar migrated outward through the porous walls, came through the craze lines in the outer glaze (which were not visible before), and on evaporation left the lead behind in the crazing pattern! So, while low expansion lead glazes might fit out of the kiln, after water-logging a piece and it will expand and craze the glaze anyway.
Lead in Ceramic Glazes
Lead is a melter in ceramic glazes and performs exceptionally well. However recent findings show it to be even more environmentally pervasive and toxic at low levels than originally thought
Is Your Fired Ware Safe?
Glazed ware can be a safety hazard to end users because it may leach metals into food and drink, it could harbor bacteria and it could flake of in knife-edged pieces.