Mexican pottery bowl purchased new c. 2007. Marked “Lead Free.” Tested positive for more than 300,000 ppm lead in the glaze when tested with an XRF instrument.
Most of the Mexican pottery that I have tested that has been labeled “Lead Free” has tested positive for at least 1,000 ppm lead. This piece was unique, coming in at more than 30% lead in the glaze!
While there is no regulation limiting the total XRF-detectable amount of lead in the glaze of decorative or functional pottery pieces, the amount of lead that is considered toxic in an item intended for children (for context) is 90 ppm lead in the coating (glaze/paint) or 100 ppm lead in the substrate (clay base, in this case.)
Conclusion: You really can’t (yet) trust the “Lead Free” label on Mexican Pottery.
As always, please let me know if you have any questions!