Expert: Sam Kelly - 3/24/2010

Question
QUESTION: I am an art teacher so I have a basic familiarity of lead based glazes.  However, I have two easy questions for someone like you....

If you are unsure if a piece of ceramic has a lead based glaze on it and it gets put into the microwave, would it cause it to spark or smoke due to lead frit or particles?

Secondly, I have a candle warmer that is made of ceramic and is glazed.  -IF- that warmer has lead based glaze on it, what are the implications of warming wax in the top of the warmer and will that filter lead based fumes/toxins into the air?  I know that lead can leach it's way into food, but I wasn't sure about it being released into the air when heated and it's implications to us breathing it.  The warmer is being heated to a temperature of approx. 125% by way of a 25 watt bulb.

Thanks so much for any info or insight into this!

ANSWER: Hi Stephanie,

If you are unsure if a piece of ceramic has a lead based glaze on it and it gets put into the microwave, would it cause it to spark or smoke due to lead frit or particles?

The answer is No, for a reaction in a micro wave to occur it needs to be metal. There are no metals in a frit.

-IF- that warmer has lead based glaze on it. The glaze would have been fired to 1000degC plus, it would have gone solid before 600degC on the cooling down in the kiln. Your 125% by way of a 25 watt bulb will have no effect on the glaze.

Sam





---------- FOLLOW-UP ----------

QUESTION: Thanks so much!  That does help.  So, if lead can be leached into food by food being put into a dish that had been fired with lead based glaze, what are the possibilities of it leaching into the wax of the warmer and released back into the air?  What would you guess could have caused the sparks and smoke?

Answer
Hi Stephanie, the concern with lead these days is null and void, that is what frits are these days. A compound fired to high temp and ground down to make a safe material to use.

The old addadge with lead is that the glaze its self was not fully vitrified, hense some leakage. The modern day glaze with a frit is totally safe, no leakage of any sort of lead will occur. The only glazes that are toxic these days are the dry glazes, these glazes once fired have no smooth sheen/glass like appearance, they are rough to touch and look like they are absorbant.

The only thing that will make a microwave sparkle and flutter is METAL. It has to be raw metal, I make pots with a high content of Red Iron Oxide, good old rust in other words, no problem in a microwave. What is in your clay BODY, is there metal in it. Fire the clay without any glaze and put it in the microwave, observe.

Nothing is going to leach out of your warmer unless its a DRY glaze.

Sam