Does this mean there's lead in it?

Use it for a violet. Don’t take a chance.

“On page 47 of John & Ron’s Cone 6 book under the heading of Testing for
Suitability for Use in a Microwave Oven, we read: “If the clay is not well
vitrified it will, more than likely, overheat and perhaps cause scalding or
burning of the person removing it from the microwave oven. It could even
crack or explode.”

Source

@marinelife I think they’re referring to the fact that unvitrified ceramic is still highly porous and so will soak up liquid, which would vaporize in the microwave and cause these problems. But that wouldn’t happen with glazed ware like a mug, and especially not on the handle.

All colored glazes get their colors from metallic oxides, and some of these get quite hot in a microwave (dark colored glazes are especially prone to this because it takes a lot of oxide to get those deep colors). The oxides used are rarely lead these days.

@Harp ; but the cup and handle was white. It was probably cheap and made in China.

White is from titanium dioxide or tin oxide, but I can’t find any good information on how these respond to microwaves. None of my cheap white mugs at home have this problem, though, so @marinelife may be on the right track. If there are flaws in the glaze that allow water to seep through to a porous clay underneath, then maybe the handle could soak up enough water in the dishwasher to get hot.

Whenever I microwave a mug and its hot, I just get a tissue so I don’t burn myself… to be honest I have never thought about lead.

If it was lead then I imagine that you would also get some sparking from the mug when its in being microwaved.

There are pens available from hardware stores which you can use on ceramics to check for lead.

There is a color change in the presence of lead.

It could just mean that it conducts heat very well.