[Natas Setiabudhi]

Hi everyone
As long as i know, the high fired glazes are safely used for food and beverage containers. But i read in some ceramic books, the glaze that contains barium oxide is harmful even have high fired. Also the glazes that contain chrome, zinc, and cooper. Is that true?
Is there any technique to determine that the containers are save as containers. I just to make sure that the plate, mug, cup that i have bought safely.
How about low fired glazes? I think the low fired glazes mostly dangerous as food and beverage containers. How about raku? i see raku wares used as container in Japan. Is that true?

[Marcia Selsor]

Natas,

There are simple leach tests using a slice of lemon. Leave it on the glaze surface for 24 hours. If you
notice any discoloration, the glaze is leaching. This is a simple test but there are more in depth tests
available. Colorants like copper,chrome, manganese, vanadium as well as barium and other heavy metals
in a not fully vitrified or mature glaze can leach. Or if there is an unbalanced quantity in a unconcerned
with safer limits recipe, the glaze can be unsafe.
I don't know what is an acceptable level of leaching if any are acceptable.

There are toxic chemicals and some are toxic in various stages other than after the firing.
Many places are making more rigid rules for disposal of water with heavy metals. My friends with
studios in Florence, Italy say it is very difficult even without using anything dangerous.
The law makers don't alwas know which chemicals are a hazard. In Montana where I taught, it was
cheaper to have the floor trap emptied and sludge hauled to the toxic dump than it was to have
it tested to see if it was toxic. The same holds true for dry chemicals. My friend in Ohio was given the
chemical contents of a studio of a deceased potter rather than have the family pay for testing of over a tone of materials.

Fumes, airborne dusts and skin contact are the means of contamination for the worker. So you need to protect yourself.
You are correct to keep reading and do research.
Marcia

[neilestrick]

The firing temperature doesn't affect safety as much as the formulation of the glaze. There are a lot of factors at work. Some glazes may leach copper, while others use it safely. American Raku should never be used with food. There are too many other possibilities to deal with here.

As for pots that you have purchased, you can do the leaching test with the lemon to see if it is leaching an metallic oxides such as copper or cobalt. But it won't tell you if it's leaching anything else. You can get a simple lead test kit at the hardware store. As for barium, cadmium or other materials, unfortunately you'll just have to trust the potter that made the pots....

[Natas Setiabudhi]

Marcia Selsor, on 19 July 2012 - 11:06 PM, said:

Natas,

There are simple leach tests using a slice of lemon. Leave it on the glaze surface for 24 hours. If you
notice any discoloration, the glaze is leaching. This is a simple test but there are more in depth tests
available. Colorants like copper,chrome, manganese, vanadium as well as barium and other heavy metals
in a not fully vitrified or mature glaze can leach. Or if there is an unbalanced quantity in a unconcerned
with safer limits recipe, the glaze can be unsafe.
I don't know what is an acceptable level of leaching if any are acceptable.

There are toxic chemicals and some are toxic in various stages other than after the firing.
Many places are making more rigid rules for disposal of water with heavy metals. My friends with
studios in Florence, Italy say it is very difficult even without using anything dangerous.
The law makers don't alwas know which chemicals are a hazard. In Montana where I taught, it was
cheaper to have the floor trap emptied and sludge hauled to the toxic dump than it was to have
it tested to see if it was toxic. The same holds true for dry chemicals. My friend in Ohio was given the
chemical contents of a studio of a deceased potter rather than have the family pay for testing of over a tone of materials.

Fumes, airborne dusts and skin contact are the means of contamination for the worker. So you need to protect yourself.
You are correct to keep reading and do research.
Marcia

Thanks for replying. is the slice of lemon just put into the container or squeezed it? The discoloration is a color change of what? the lemon or the glaze surface?

[Natas Setiabudhi]

neilestrick, on 20 July 2012 - 01:57 AM, said:

The firing temperature doesn't affect safety as much as the formulation of the glaze. There are a lot of factors at work. Some glazes may leach copper, while others use it safely. American Raku should never be used with food. There are too many other possibilities to deal with here.

As for pots that you have purchased, you can do the leaching test with the lemon to see if it is leaching an metallic oxides such as copper or cobalt. But it won't tell you if it's leaching anything else. You can get a simple lead test kit at the hardware store. As for barium, cadmium or other materials, unfortunately you'll just have to trust the potter that made the pots....

Thanks for replying. May be we should believe and be kind thought to them. If they doing wrong, they will pay afterlife, hahahah..

[Marcia Selsor]

Natas Setiabudhi, on 20 July 2012 - 01:50 AM, said:

Marcia Selsor, on 19 July 2012 - 11:06 PM, said:

Natas,

There are simple leach tests using a slice of lemon. Leave it on the glaze surface for 24 hours. If you
notice any discoloration, the glaze is leaching. This is a simple test but there are more in depth tests
available. Colorants like copper,chrome, manganese, vanadium as well as barium and other heavy metals
in a not fully vitrified or mature glaze can leach. Or if there is an unbalanced quantity in a unconcerned
with safer limits recipe, the glaze can be unsafe.
I don't know what is an acceptable level of leaching if any are acceptable.

There are toxic chemicals and some are toxic in various stages other than after the firing.
Many places are making more rigid rules for disposal of water with heavy metals. My friends with
studios in Florence, Italy say it is very difficult even without using anything dangerous.
The law makers don't alwas know which chemicals are a hazard. In Montana where I taught, it was
cheaper to have the floor trap emptied and sludge hauled to the toxic dump than it was to have
it tested to see if it was toxic. The same holds true for dry chemicals. My friend in Ohio was given the
chemical contents of a studio of a deceased potter rather than have the family pay for testing of over a tone of materials.

Fumes, airborne dusts and skin contact are the means of contamination for the worker. So you need to protect yourself.
You are correct to keep reading and do research.
Marcia

Thanks for replying. is the slice of lemon just put into the container or squeezed it? The discoloration is a color change of what? the lemon or the glaze surface?

put a slice of lemon on the glaze in question and leave it there for 24 hours. If the glaze changes color or character it will be obvious.
Marcia

[JBaymore]

This is a HUGE subject..... with lots of "it depends" type answers...... and is something I have been covering in my current NHIA college-level ceramic chemsitry classes as well as since I was teaching that subject at MassArt and the BU PIA back in the 70's and 80's.

Get and read "Keeping Claywork Safe and Legal" by Mononna Rossol from the NCECA bookstore.

Get and read "Artist Beware" by Dr. Michael McCann from Steven Branfman's "Potter's Shop Bookstore".

Get and read "Mastering Cone Six Glazes" by John Hesselberth and Ron Roy from Steven Branfman's "Potter's Shop Bookstore".

Go the the US FDA website and study the lead and cadmium foodware regulations.

Go to the Digitalfire.com website and start researching understanding the fundamental of glaze chemistry. Download the free demo version of Insigfht software.

That grounding will start you on the road to understanding the potential situation.

best,

..........................john

[Lendar]

Hmm, Interesting. I have used glaze many times without any protection. I will do some reseach regarding this topic.

[Marcia Selsor]

Don't forget the Material Safety Data Sheets supposedly supplied my manufacturers or distributors.
MSDS information should be available for everything chemical you use..

Marcia