Really interesting.

From the article: "Total Lead content in the glaze or coating of modern mugs (as detectable with an XRF) is not regulated. As long as mugs are not leaching Lead at the time of manufacture (when they are brand-new), they are considered to be safe to use — even if the Lead content of the glaze is very high. However, for context, the amount of Lead considered unsafe (and illegal) in the paint, glaze or coating of a newly-manufactured item manufactured and sold as “intended for use by children” is 90 ppm or higher. The good news is that, since children’s items are regulated for total Lead content (as of 2008), newly-purchased children’s mugs legally must have coatings below 90 ppm Lead [and my findings have confirmed that manufacturers are generally complying with this law — although I recommend sticking with children’s items manufactured in 2011 or later, as it took a while for the companies (and their supply chains) to get up to speed in their compliance with the new regulations]."

FWIW, every "recommended" mug in her current list is a glass mug, not a ceramic glaze mug. Which is no problem for me but this doesn't answer the original question.

As a matter of fact, I ordered a new glass mug set from Amazon using a link in her article (which I assume is an affiliate link) out of gratitude for her work.