katie rose on sat 13 apr 96
hi ron,
thanks for your reply re: toxic?
>Depends on how durable the glaze is. Some glazes are easily attacted by
>acids and sometime alkalies.
do you know where i could find out more about this?
>
>I wrote an article once titled "All Glazes Leach" - question is how much
is your article available?.
thanks!
katie rose
***********************
katie rose
raven@sedona.net
"Love is the reflection of God's unity in the world of duality. It
constitutes the entire significance of creation." (Meher Baba)
Ron Roy on tue 16 apr 96
katie rose wrote
>----------------------------Original message----------------------------
>hi ron,
>thanks for your reply re: toxic?
>>Depends on how durable the glaze is. Some glazes are easily attacted by
>>acids and sometime alkalies.
>do you know where i could find out more about this?
>>I wrote an article once titled "All Glazes Leach" - question is how much
>is your article available?.
>thanks!
>
>katie rose
Hi Katie,
You already know how to get a copy.
In my work with glaze calculation software I use "limit formulas." Limit
formulas are: A set of upper and lower oxide limits for glazes within
certain cones. When I am working on, lets say a cone 6 glaze and using the
Seger molecular formula, I then have some idea of how much silica it takes
to make a good glass - in this case 2.5 to 3.5 mols of SiO2. I used to
wonder if these guide lines were reliable but now have evidence I can trust
them. I am sure there will be some examples of good glass outside of the
limits and some glazes within won't be durable but they will be the
exceptions.
One test for durability. Glaze two pieces of clay - leave one piece in the
dishwasher forever and keep the other out. Compare the two every once in a
while (with a magnifying glass) - the one in the dishwasher will dull over
time - or not. The rate at which the glaze dulls will indicate durability
in relationship to attack by alkali. This is not exactly a scientific test
but is a pratical indicator.
There are many descriptions in texts on pottery about measuring durability.
I would cauction against the use of short term tests and recommended "in
sevice" testing using common foods like tea, coffee, vinegar. Always have
an untested (unused) sample to compare with. Remember, heat helps the
reaction so putting tests in the refrigerator will slow things down.
I am sure this kind of testing will be of great interest to the community.
I just don't have time to do it. If there is someone or group out there who
wants to get into this we will all benefit.
How can I be sure my glazes are not a problem? I don't use poisons in my
glazes - If I did I would not use those glazes on food bearing surfaces. If
I did use poisons in glazes on food bearing surfaces I would have those
glazes tested for durability.
Yes, you guessed it, I've been an organic gardner for 30 years.
Ron Roy, Toronto, Canada
Paul Huel on fri 26 apr 96
In message "Re: for Ron--Re: toxic ?", Ron Roy said:
Hi Ron,
I don't know if you remember me, but I did ask you some
questions about glaze toxicity a while back, I meant to get back
to you about it, but was gone for a couple of weeks, then
unfortunately lost my message database.
>I am sure this kind of testing will be of great interest to the community.
>I just don't have time to do it. If there is someone or group out there who
>wants to get into this we will all benefit.
>How can I be sure my glazes are not a problem? I don't use poisons in my
>glazes - If I did I would not use those glazes on food bearing surfaces. If
>I did use poisons in glazes on food bearing surfaces I would have those
>glazes tested for durability.
Does this mean that you don't use cobalt, nickel, manganese etc
in any of your glazes?
>Yes, you guessed it, I've been an organic gardner for 30 years.
We can't be more than a couple of years behind you in organic
gardening.
thanks
Paul
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<> Kispiox Valley, B.C. Canada <>
<> email: bella@netshop.net <>
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