Dai Scott on wed 5 aug 98
Well-said, Earl Brunner. Your comments make a great summing up of what has
been a very long discussion of a simple question---that being, simply, "how
much to charge?"
(snip)
Regarding the barium question: a couple of years ago, when I first came
across recipes using barium and heard of its toxicity, I made a number of
phone calls to various levels of government agencies to find out what I
could about the finished product being a danger to my customers. On every
level, I was warned about the dangers to myself, using it in the raw state,
but was told that once it is fired in a glaze, that it changes from a
carbonate to an oxide, which is not toxic. Also, as long as the glaze was
fired to maturity, and not underfired, there should be no danger of anything
toxic leaching out. I have since used a few barium glazes, all of which
have small percentages of barium, but not usually for dinnerware, mainly
because of their mattness, which makes for unpleasant sound effects when
cutlery is used on their surfaces.
So, not that I would doubt anything the government told me , but was this
proper information or not?
(snip)
Dai Scott - Pottery by Dai - Kelowna, B.C.
Craig Martell on thu 6 aug 98
>Regarding the barium question: I made a number of
>phone calls to various levels of government agencies to find out what I
>could about the finished product being a danger to my customers. On every
>level, I was warned about the dangers to myself, using it in the raw state,
>but was told that once it is fired in a glaze, that it changes from a
>carbonate to an oxide, which is not toxic. Also, as long as the glaze was
>fired to maturity, and not underfired, there should be no danger of anything
>toxic leaching out.
>So, not that I would doubt anything the government told me , but was this
>proper information or not?
Hi:
The info you got from "various" government agencies was kinda incomplete
according to what I know about glaze composition. Of course you can always
question my capabilities in this area as well!
The carbonate to oxide statement is pretty meaningless as fired glazes with
barium can leach Ba. The TOTAL composition of the glaze is the key factor
to suitability in functional ware. You can fire a glaze to maturity but if
it is short of silica and or alumina leaching could happen. I'm not in
favor of deleting barium from glazes altogether but I am in favor of
knowlegeable glaze composition and testing to insure safety to customers.
Ron Roy has stated many times that there are no simple answers to these
questions and I stand behind him on that. Sometimes, we want someone in
higher authority to tell us everything will be fine IF..... But the
responsibility is with the maker I believe. We need to have an
understanding of the materials and how to use them and when not to use them
etc. etc. and it is up to us to find answers to questions about specific
formulas and receipes that we are using.
regards, Craig Martell-Oregon
Ron Roy on thu 6 aug 98
I am trying to resist the temptation but cannot - if you want accurate
information don't ask the government - well not in this case anyway. Toxic
release from a glass or glaze has to do with it's resistance to chemical
attack - you cannot tell by looking at a glass or glaze whether it is
durable. Neither can you tell by the temperature it was fired to. In the
end you can only tell if you test the glaze to determine what comes out and
how much. If fact all glazes leach - given the right circumstances and
enough time - the question is how much.
There are guidelines for helping to determine durability of glazes - called
limit formulas. They are used in conjunction with the Seger unity molecular
formula to determine if the fluxes, silica and alumina are present in the
proper amounts for the fired temperature.
There is a case for small amounts (1 or 2 %) of Barium in a mid range glaze
to help with the melt but Strontium will do the same thing - from what I
have been reading perhaps even better. I am not talking about matte glazes
here - which I agree are not suitable for food - for many reasons. If you
do want to use a matte glaze for food - the best strategy would be to have
no toxins present in glaze or decoration.
I know there are conflicting opinions about the use of the many toxic
materials which are available to us. I also know there are great gaps in
our knowledge about these materials - especially when they are combined in
us. The chemical soup we live in is getting thicker - certainly not
thinner. It seems to make sense to me to add as little to the soup as
possible - especially when I am making ware that can be used for serving
and storing food.
I know this sounds like a sermon - it's not. This is how I feel about it -
it has become part of my craftsmanship - what I care about. I find it
reassuring that many others have "taken the Barium off the shelf" at least
until there is the necessary knowledge to use it in a safe way.
>----------------------------Original message----------------------------
>Regarding the barium question: a couple of years ago, when I first came
>across recipes using barium and heard of its toxicity, I made a number of
>phone calls to various levels of government agencies to find out what I
>could about the finished product being a danger to my customers. On every
>level, I was warned about the dangers to myself, using it in the raw state,
>but was told that once it is fired in a glaze, that it changes from a
>carbonate to an oxide, which is not toxic. Also, as long as the glaze was
>fired to maturity, and not under fired, there should be no danger of anything
>toxic leaching out. I have since used a few barium glazes, all of which
>have small percentages of barium, but not usually for dinnerware, mainly
>because of their mattness, which makes for unpleasant sound effects when
>cutlery is used on their surfaces.
>So, not that I would doubt anything the government told me , but was this
>proper information or not?
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
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