Bob, Most ceramic tile produced prior to 1978 contained large quantities of LBP. The lead is between the clay and the glaze or in the glaze itself (in some cases), and is often 30-40 times the quantity specified by the federal standard for lead in paint.
Since, 1978 the imported ceramic tiles from Spain, Italy, and Mexico contain huge amounts of lead. I haven't found any US tile manufactured since 1978 to contain lead.
The tile is safe, due to the hardness of the glaze, once it is installed and cleaned. However, installers and renovators often create huge amounts of lead dust cutting and removing the leaded ceramic tiles. Federal import laws only require country of origin, not lead content in the imported tiles. Consequently, we've got contractors putting these leaded tiles in new construction homes, often with disastrous results. The safety are often simple and very cheap, but most contractors don't realize that they are dealing with a legal time bomb.