Lead and teaware...Is this safe?

[Dresden]

Hello,

I recently purchased some vintage kutani ware. Upon using a lead test it was found that there was no lead detected on the inside of the cups, or on the non-painted area on the back of the cups.

The paint used to decorate the outside of the cups does test positive for lead content.

Question is, would you consider these cups safe for use?

[Chip]

Question is, would you consider these cups safe for use?

Would you consider this safe? Thanks for posting this as there is a difference in glazing in some teawares inside versus outside!

I am putting Kutani on my list to be careful in buying and using!

Is this an older piece?

[Dresden]

I would say probably 40-50 years old.

Its actually not the glaze that is reactive. It the decorative items painted on the outside (trees etc). When you rub the outside you can actually feel that this paint is a raised surface as if it would have been added after the glazing process.

[JBaymore]

Most overglaze enamels were and still are lead based glazes.

The famous "Kutani red" is a specific formulation containing exactly the right molecular ratio of lead oxide, silica, and red iron oxide. The other traditional Japanese overglaze enamels are also lead flux based. Of particualr concern for lead release is thje green colors; the presence of copper greatly increases the leaching of lead out of any firing range glaze.

All of the older overglazed Kutani, Nabeshima, Imari, Arita, and so on porcelains will have lead based overglaze.

I am not sure if any of the Japanese porcelain producers have switched over to non lead bearing overglazes. Maybe Robert Fornell will know? I seem to remember reading that in Japan the overglazes in addition to the raku glazes are exempted from lead release standards. (Shows the importance of the aesthetics of ceramic art to the Japanese. )


I use commercially prepared overglaze enamels on my work that are lead free on any food contact surfaces. The sources here in the USA are limited, as are the colors.

best,

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

[JBaymore]

It the decorative items painted on the outside (trees etc). When you rub the outside you can actually feel that this paint is a raised surface as if it would have been added after the glazing process.

Dresden,

This process is called overglaze enamel.

The porcelain piece is first fired to a high temperature (maybe about 2350-2400F) with the base glaze applied. This glaze can be over an underglaze painting of cobalt compounds that produce the typical blue color.

Then after that high tempeature firing, the ceramist paints a low temperature glaze onto the already fired glaze surface. This "overglaze" is formulated so that it fuses a bit onto the surface of the underlying high fire glaze. Then the piece is put back into another lower temperature firing (maybe 1300-1400F) and the overglaze is fused.

The overglaze IS another layer on top of the background glaze.

So the background glaze likely would never contain any lead compound, since lead would basically volitalize out of the melt at the high temperatures and go off in the kiln exhaust gases. But the overglaze likey will contain lead .... because to get glazes to fuse in that low temperature range, there is a limited array of fluxes on silica that will work. Unfortunately, lead is the BEST of them from the ceramist's point of view, hands down. It just has that one pesky little drawback..........

best,

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

[MarshalN]

I honestly can't imagine it will leak enough lead for you to really have to worry.

[kilgoretrout]

A very small amount of lead, in most chemical forms, can be considered toxic. The CDC says that 10 micrograms per deciliter of lead in the blood has measurably toxic effects on a child (http://www.atsdr.cdc.gov/csem/lead/pb_standards2.html). A human has about 60 deciliters of blood, meaning 600 micrograms (millionths of a gram) of lead is harmful.

If it were me, I would do more research about the teapot to make sure it is safe to use.

[entropyembrace]

the lead is on the outside surface, I wouldn´t worry about it...it´s not going to travel through the glaze and clay to attack your tea xD

[JBaymore]

Entropye is correct on this thought. The outside does not really affect the inside.

If you have old Japanese or Chinese porcelains with overglaze enamel painting on the inside surfaces, then I would not be using them for food.

"Lovely to look at
Lovely to hold
But if you eat out of them
Your brain cells will fold."

best,

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

[gingkoseto]

Good to know - both about kutani containing lead and about in-glaze paint being safe. Thanks!

Then about the paint with lead on the outside - will it cause danger by skin contact?

Oh! Just thought of this - is the red mosquito on my avatar the lead-containing red paint?

[JBaymore]

Good to know - both about kutani containing lead and about in-glaze paint being safe.

Only Kutani (et al) that has overglaze enamels contains lead... and it is only in the composition of the overglaze itself. The high fire glazes on the porcelain that are the ground onto which overglaze is painted and fired onto do not contain lead compounds. As I mentioned elsewhere on this board, the green overglaze is more of a problem with lead release than the red or other colors.

And please don't extrapolate the concept into ".....in-glaze paint being safe". It depends a lot on what ceramic material is being painted "in-glaze", and how that material affects the chemistry of the area of glaze it "stains". Use of materials like pure or almost pure oxides as a painting medium under or over a powdered glaze layer can sometimes supersaturate the glaze in that area with colorant that the cooling melted glaze layer cannot hold in solution.

If that colorant has toxic properties, then it is possible that painted area of the piece will tend to leach that material. If you are painting with iron oxide....... well..... most people can use a bit more iron in their diet . But if you are using a non-encapsulated cadmium bearing stain, then you certainly will possibly have "issues".

Then about the paint with lead on the outside - will it cause danger by skin contact?

Good question. At a very, VERY "technicallity level" (meaning so small an issue as to likely be of no worry at all), there can/will form a minute film of white lead oxide on the surface of the lead based glaze as some of the lead which is loosely bonded into the glass matrix oxidizes from contact with the oxygen in the air. This is similar to what happens with the surface of lead paint, but the paint holds the lead far less tightly bonded than the glaze does.

Oh! Just thought of this - is the red mosquito on my avatar the lead-containing red paint?

Ginko, Can't tell from the photo precisely, but likely that is the case.

There are limited ways to produce a blood red in ceramics. One is finely ground iron and lead oxide at low temperatures. Another is a precidely formulated and reduced copper bearing glaze at high temperatures. The third (which is more "pink-ish") is a combination of chromium oxide with the exact right molecular ratio of tin oxide. And the last is a coloring stain composed of cadmium sulfide and selenium oxide.

That form of Cd stain is also availabe in what is called an "encapsulated" format. What that means is that the little, already stabilized, red particles are surrounded in a little "bubble" of zirconium glass. This prevents the cadmium compounds from leaching out of the bubble. Expensive!!!

best,

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

[Victoria]

I honestly can't imagine it will leak enough lead for you to really have to worry.

This is really how I feel too. I am not really wanting to "fight" the issue, but if the inside is safe, and there is some unsafe outside, for the brief amount of time it touches your lips, and the small amount of surface area involved for this brief time, I can't imagine enough would leech to even be measurable. So I proceed cautiously, keeping in lesser rotation anything I feel maybe of this category. I certainly would not make it my daily cup, but I would not worry about using it occasionally.

If it is so toxic you shouldn't even be taking a sip from it, then you shouldn't even be handling it.

[entropyembrace]

our food is covered in pesticides and often has toxic chemicals added for various reasons like colour and to increase shelf life....I don´t think a trace of lead on the outside of our cups matters...

heck I ate tuna subway yesterday....that probably has more lead in it xD

[JBaymore]

heck I ate tuna subway yesterday....that probably has more lead in it xD

It is a lot of mercury that is in tuna.

And yes..... lead in the glaze on the outside is no issue.

best,

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

[entropyembrace]

lead levels are almost equal to mercury in tuna fish....there´s a fair bit of cadmium too.

http://www.sciencedirect.com/science?_o ... f2ccd25ea8