amy parker on fri 2 apr 99
Tony - You said:
>Yikes! It's there to make the black, if it's black it didn't burn out.
>I had a similar experience at NCECA where a well known author told me:
>"Every ceramic engineer will tell you that lead is completely harmless
>as long as it is fritted"!
You know - I just had someone tell me this very "fact" about lead frits
yesterday!!! Am I nuts, or is the lead in the frit going to get into the
kiln (electric) walls & the atmosphere & any wet foods put into the pots?
Several of us can't see how you can "lock up" the lead molecules - after
all, they are obviously interacting with the rest of the mix to give the
melt and colors, so it CAN't be like the lead is really "locked up" -
can it??? I didn't want to argue the point when under-informed...
amy parker Lithonia, GA
amyp@sd-software.com
Craig Martell on sat 3 apr 99
>Yikes! It's there to make the black, if it's black it didn't burn out.
>I had a similar experience at NCECA where a well known author told me:
>"Every ceramic engineer will tell you that lead is completely harmless
>as long as it is fritted"!
Hi:
This lead stuff comes up and hangs out almost as much as the Handmade posts
or Barium toxicity!
The above statement about lead frits needs some qualification I would think.
Harmless in what way? In the raw state this would certainly apply but as
far as fired glazes are concerned, the above is meaningless. Unless a glaze
is properly compounded and has enough silica and alumina to be durable and
hard, lead is going to leach regardless of it's state when intoduced into
the glaze batch. Lead doesn't know if it's fritted or raw, once it has
entered into a melt with other glaze ingredients in the kiln. Frits don't
make everything hunky dory and that is not their primary purpose.
My feeling is: Don't use any kind of lead in glazes that will contact food.
There are many other glaze types for all temps that don't need the kind of
concern and constant testing and observation that lead glazes need.
regards, Craig Martell in Oregon
Tom Buck on sat 3 apr 99
Amy:
A small number of companies make the special glasses called frits
to help industrial ceramic producers maintain uniform production
standards. We potters are along for the ride.
In simplest terms, a frit is a type of glass (metal+silica, or
metal+alumina+silica, or metal+boria+alumina+silica) that melts along with
other components in a glaze recipe. This happens with a leaded frit. The
new liquid intermingles all components so the PbO (lead oxide) molecules
are freed to wander about and find a new position in the new glassy matrix
(network) which forms the fired glaze.
The question then becomes: Is the new glass (ie, the glaze on a
pot) durable and stable so that it withstands corrosive attack from things
like vinegar and orange juice (acidic foods)? If the glaze releases lead
to the food, then it poses a danger to people especially children.
The use of a frit in a glaze recipe has merit because it will
supply certain components to the fired glaze in high purity and be
consistent bag-to-bag, year-to-year. But a frit does NOT guarantee that
toxic metals will be permanently locked away from future chemical
activity.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East 43rd
St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of Ontario,
Canada).
Eric Suchman on fri 18 may 07
I was wondering ..... If I use a lead frit in a gas updraft and fire
it to ^04, then later do a ^6 glaze fire of totally different ware,
is that sufficient to burn out whatever lead residue might be lying
around in the bricks from the previous firing?
Like wise in an electric?
Thanks,
Eric Suchman
Kathy Stecker on sat 19 may 07
Eric asks:
"I was wondering ..... If I use a lead frit in a gas updraft and fire
it to ^04, then later do a ^6 glaze fire of totally different ware,
is that sufficient to burn out whatever lead residue might be lying
around in the bricks from the previous firing?
Like wise in an electric?"
Eric I've been curious about something similar. Someone here has been using
low fire reds and other colors
to decorate pots for the cone 10 gas kiln. I'm not sure if fritted lead is
being used or cadmium in the reds-but if they are, how much do I need the worry
about my food safe ware? So something volatilizes but how much traps again
elsewhere?
Thanks,
Kathy Stecker
Winter Springs, FL
************************************** See what's free at http://www.aol.com.
Ron Roy on sun 20 may 07
Hi Eric,
I don't think you ever get all the lead out - the question is rather - how
much is deposited on the ware in subsequent firings and is it significant?
If reduced the problem gets worse because lead oxide is easily reduced to
lead which means it's even more volatile.
If you have the functional pots tested you will find out if they pass.
California has the most stringent laws for lead anywhere - and fines to
match.
RR
>I was wondering ..... If I use a lead frit in a gas updraft and fire
>it to ^04, then later do a ^6 glaze fire of totally different ware,
>is that sufficient to burn out whatever lead residue might be lying
>around in the bricks from the previous firing?
>Like wise in an electric?
>Thanks,
>Eric Suchman
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ron Roy on sun 20 may 07
Hi Kathy,
Just have some mugs tested for lead and cadmium - there are lots of labs
around that will do this for about $35.
I would not fire either it in my kilns.
RR
>Eric asks:
>"I was wondering ..... If I use a lead frit in a gas updraft and fire
>it to ^04, then later do a ^6 glaze fire of totally different ware,
>is that sufficient to burn out whatever lead residue might be lying
>around in the bricks from the previous firing?
>Like wise in an electric?"
>
>Eric I've been curious about something similar. Someone here has been using
>low fire reds and other colors
>to decorate pots for the cone 10 gas kiln. I'm not sure if fritted lead is
>being used or cadmium in the reds-but if they are, how much do I need the worry
> about my food safe ware? So something volatilizes but how much traps again
>elsewhere?
>
>Thanks,
>Kathy Stecker
>Winter Springs, FL
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
| |
|
