Brenda Phillips on wed 21 dec 05
How do you test a glaze to be sure that it is food safe?
John Hesselberth on thu 22 dec 05
On Dec 22, 2005, at 12:07 AM, Brenda Phillips wrote:
> How do you test a glaze to be sure that it is food safe?
Hi Brenda,
Legally a glaze is "food safe" in the U.S. if it doesn't contain lead
or cadmium or passes the leaching test for those materials. Other
countries may have other requirements. That, in my opinion, does not
mean it is suitable for use on functional work. I no longer use the
term "food safe" except in notes like this because it has no
meaningful definition. I prefer to ask how durable or stable a glaze
is. I have seen some glazes that leach nearly all of their colorant
(e.g. copper or cobalt or others) into food when exposed to acidic
foods, e.g. citrus, tomatoes, etc. Whether or not that is safe I
won't debate--I don't like it and get pretty disgusted when I find a
pot that behaves that way. I own a couple mugs at the moment that I
use as demonstrations of this happening on exposure to coffee.
So what is a potter to do? For a starter, you might visit my web site at
http://www.frogpondpottery.com/glazestability/stableglazes.html
and read that page on glaze stability. Click on the highlighted word
'instructions' to learn how to have your glazes leach tested at
moderate cost. If you want to learn even more about the subject a
good part of chapters 1, 3 and 4 of Mastering Cone 6 Glazes is
devoted to this subject of glaze stability and suitability for use on
functional pottery.
I hope this helps. The bottom line, though, is you will have to set
your own standards for what you are willing to put out into the world
(with the exception of lead and cadmium which are regulated in the
U.S. and most other countries). Good luck.
Regards,
John
Sarina Grey on fri 23 dec 05
Brenda,
Individual states have different regulations about what metal content is
legal and how a piece must be labeled if lead/cadmium levels are above the
maximum allowable for food ware. You should look into specific laws
applicable to where you sell your work - arguably, even an item you and I
might consider to be "safe" may not be okay. On the other hand, you don't
always need to go overboard, since there are certain allowances such as
where the lead-containing glaze might be located on a cup (i.e. not around
the lip part or in contact with the contents).
I looked into this for a friend when he was concerned about little trinkets
he decorates (it turns out they were no problem, but better to be safe than
sorry). I use the site http://www.unleadeddecal.com as a jumping point for
reference whenever a new question comes up - it has a lot of links that
aren't specific to just decals and information about the testing and
labeling requirements. I'm going to check out John's site now, too.
Good luck - I can't get over how complicated all these laws can be.
-Sarina
On Thu, 22 Dec 2005 09:08:37 -0500, John Hesselberth
wrote:
>On Dec 22, 2005, at 12:07 AM, Brenda Phillips wrote:
>
>> How do you test a glaze to be sure that it is food safe?
>
>Hi Brenda,
>
>Legally a glaze is "food safe" in the U.S. if it doesn't contain lead
>or cadmium or passes the leaching test for those materials. Other
>countries may have other requirements. That, in my opinion, does not
>mean it is suitable for use on functional work. I no longer use the
>term "food safe" except in notes like this because it has no
>meaningful definition. I prefer to ask how durable or stable a glaze
>is. I have seen some glazes that leach nearly all of their colorant
>(e.g. copper or cobalt or others) into food when exposed to acidic
>foods, e.g. citrus, tomatoes, etc. Whether or not that is safe I
>won't debate--I don't like it and get pretty disgusted when I find a
>pot that behaves that way. I own a couple mugs at the moment that I
>use as demonstrations of this happening on exposure to coffee.
>
>So what is a potter to do? For a starter, you might visit my web site at
>
>http://www.frogpondpottery.com/glazestability/stableglazes.html
>
>and read that page on glaze stability. Click on the highlighted word
>'instructions' to learn how to have your glazes leach tested at
>moderate cost. If you want to learn even more about the subject a
>good part of chapters 1, 3 and 4 of Mastering Cone 6 Glazes is
>devoted to this subject of glaze stability and suitability for use on
>functional pottery.
>
>I hope this helps. The bottom line, though, is you will have to set
>your own standards for what you are willing to put out into the world
>(with the exception of lead and cadmium which are regulated in the
>U.S. and most other countries). Good luck.
>
>Regards,
>
>John
>
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