View Full Version : Leaded glaze
05-09-2007, 08:02 AM
I've been trying to track down good information on leaded glaze and safety. I've found a few opinions on a few sites. But they aren't well supported. My basic question is - Is there a legitimate concern over leaded glaze in older pottery? If so, when is the cut off date? 1980s? This shouldn't be a concern for reproductions.
05-09-2007, 08:46 AM
While I can not speak towards how much lead will leach from the glaze in older pottery (it would be an interesting research project however), I can speak about the relative dangers to adults versus children. Lead is a toxin that retards the development of the networking of nerves that is part of the learning process of children. Therefore, I would be much more careful about using items with lead glaze around young children than around adults. The levels at which lead affects children is considerably lower than the levels that affect adults.
05-09-2007, 09:30 AM
Yes, the concern is valid.
Here's one path to go down in looking at the various points of concern, even with modern safety techniques. http://www.frogpondpottery.com/pottalk/lead.htm
Some concerns even with modern glazes:
Often we a faced with the lack of available reproductions for period items. A bit of poking around an arts fair, or a university department should produce a competent wheel potter willing to copy a period wheel-thrown piece from illustrations and measurements, and a reasonable modern substitute glaze in an appropriate finish.
05-09-2007, 10:40 AM
Thank you both for your replies. This helps me understand lead and lead glaze much better.
This tells me I should review which items I am using during events. Some of them may be better left on a shelf at home. I feel safe about the pottery pieces that come from the local museum's potters. I am not sure about a few of the stoneware pieces I picked up elsewhere. Also of possible concern are the other dishes I use including some ironstone and silverplate. Then there are the pewter pieces that up to this point are for looks only.
05-09-2007, 10:45 AM
Along those same lines, you might find a local high school art teacher willing to throw what you need. Art teachers have to do demonstrations for students on a frequent basis. Your piece could be one of those demos. If you approach an art teacher about the time they are doing ceramics you might get your piece fired and glazed as well.
05-09-2007, 02:10 PM
Some concerns even with modern glazes:
I would like to re-iterate and empahsize a point brought up in the above link. If in doubt about whether or not the glaze contains lead, do not, I repeat do not, use it to hold foods containing acidic ingredients such as citric fruits, vinegar, tomatoes, etc. The acid in these foods can significantly affect the rate at which lead can leach out of the glaze into the foods. This increase in leaching of toxic metals is a well established occurrence in Environmental Chemistry. In fact, the EPA actually uses the active ingredient of vinegar to perform "worst-case" tests for the leaching capabilities of materials to determine whether or not they qualify as hazardous wastes.
05-09-2007, 05:58 PM
Anna, contact John-Owens Kline on the AC. He is a member of a well connected six generation family of potters. He is strictly interested in traditional potters, not the trendy modern potters that produce modern goods loosely based on traditional styles.
05-12-2007, 07:05 AM
To test your stoneware for a lead glaze…
You will need:
- Household vinegar or 5% acetic acid
- A saturated solution of potassium iodide (check with your local hobby store or druggist)
- A diluted solution of hydrofluoric acid (aka Whisk-Away a rust remover for clothing)
Mix equal parts of acetic acid and potassium iodide solution (1 cc. each) Apply one large drop this this mixture to the glaze to be tested. On top of this place one drop of they hydrofluoric acid. Within 5 minutes, often within 1 minute, a yellow-orange precipitate will appear within the drop if lead is present in the glaze.
05-12-2007, 08:29 AM
Almost any hardware store will carry a inexpensive kit to test for lead. Very simple to use. In our business we work around lead a good bit and by law we have to educate our clients about the potential risk. I personally would test ANY piece new or old unless I was absolutely sure it was lead free. I once bought some new pottery made in China that tested positive for lead. Also be aware that sometimes the sealed surface may be lead free but underneath may not be. If there is a chip, test the chip. I have been surprised more then once.
05-15-2007, 07:51 PM
High fired ceramics won't have lead in their glaze. It would burn out and be useless as a glaze component. High fired ceramics are vitreous, that is they are not porous even where there is no glaze. Porcelain (actual porcelain not just white clay), reduction ware and true stoneware are all high fired. (Cone 10 and above, 2500 degrees or higher.)
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