Steven D. Lee on fri 13 sep 02
Do you think that a container would be food safe if I used these
oxides and a commercial food safe cone 5 glossy white glaze in the
200g distilled water
1.7g cobalt oxide
3g copper carbonate
Application: sprayed on cone 03 bisque, covered with cone 5 glossy
white glaze also sprayed x3 over the wash.
Firing: Oxidation to Cone 5 soak for 30 minutes
karen gringhuis on sun 15 sep 02
Regarding food safety in general, particularly
"commercial"!!? safety - whatever you do & whatever
anyone says, have multiple fired pieces PROFESSIONALLY
tested. And consider buying product liability insurance.
Box 607 Alfred NY 14802
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John Hesselberth on sun 15 sep 02
On Friday, September 13, 2002, at 11:05 AM, Steven D. Lee wrote:
> Do you think that a container would be food safe if I used these
> oxides and a commercial food safe cone 5 glossy white glaze in the
> following way:
> 200g distilled water
> 1.7g cobalt oxide
> 2.4g rutile
> 3g copper carbonate
> Application: sprayed on cone 03 bisque, covered with cone 5 glossy
> white glaze also sprayed x3 over the wash.
> Firing: Oxidation to Cone 5 soak for 30 minutes
The only answer I can give is a definite maybe. First, just because your
commercial glaze is "food safe" says nothing about its durability.
Different manufacturers of glazes use that term in different ways. For
example one may say it is food safe just because it has no lead or
cadmium or because it does have lead or cadmium and meets the government
standards for leaching. Another may say it is food safe because it
contains nothing but clay, feldpar, a boron frit and some opacifier.
Others seem to use other definitions (or no definition at all). There
are a least one or two who test their glazes rigorously and submit the
results to an industrial toxicologist for an opinion. Unfortunately, I
think they are in a tiny minority.
Then there is the question of durability. I have found some commercial
glazes labeled food safe that are of extremely poor durability, i.e. I
can take the color right out of them by exposure to lemon juice or
vinegar for a couple hours.
I will say this. If your commercial "food safe" glaze is durable to the
standards we set for ourselves in "Mastering Cone 6 Glazes" then the
odds are pretty good that what you are doing is OK.
But Karen is right. The only way to know is to have your particular
combination professionally tested. For instructions on how to do this
you can go to my web site at www.frogpondpottery.com or find detailed
instructions in the book referenced above.
All this makes a stong point in favor of mixing your own glazes--at
least you know what is in them and can make an educated judgement
regarding their stability with the help of glaze calculation software.
Frog Pond Pottery
PO Box 88
Pocopson, PA 19366
Fax or phone: 610-388-1254