antique porcelain toxicity? safe to drink from old ceramic?

[brandon]

I can see you are very frustrated with the lack of lethal effect of your teaware collection. Have a housemate you don't care for?



You might be interested in investing in some carved Cinnabar teaware.

[Midwinter_Sun]

Some studies show that even NEW ceramics contain lead in higher levels than considered healthy.

I suggest getting ceramics that are not decorated or made without lead to begin with.

This is a fairly recent paper

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3576496/

"The FDA has recognized China as a source of lead-contaminated ceramics since the 1980s, and it continues to be a problem today "

A follow up on the study -
https://janestreetclayworks.wordpress.c ... zes-story/

I would suggest you do a lead check with a kit, alternatively, if you are not in the US / Europe, in many Asian countries you can easily find the chemicals to do the test yourself for cheap, under USD $10 for chemical that will be enough for years.

You will need vinegar and Sodium rhodizonate / Potassium rhodizonate

http://www.home-health-chemistry.com/Le ... ction.html
http://www.instructables.com/id/Making- ... -Chemical/

Another source of worry for ceramics and glazes is cadmium and other heavy metals.

I do have raku ware that is old or traditional made ( with lead oxide glazes) , and I enjoy a cup of Matcha from them now and then.
They are lead positive.
I am still here and healthy.
would I make them my daily cup? No. And the water going into them is only 80 degrees celcius, not boiling.

That said, just going out on the street on a busy traffic day puts more heavy metals into my blood.

[Bok]

Thanks for your input! Has been a topic which I have been researching recently as well. Bought some maybe-antique cups

[Midwinter_Sun]

Thanks for your input! Has been a topic which I have been researching recently as well. Bought some maybe-antique cups

I think the largest threat is for "normal" people, with "normal" ware.

For example, people mix tea with spoons, use utensils, that means heavy wear and tear, people eating off the ware and wearing the glaze out, using dishwasher,scraping ware with heavy scrubbing, chipping with heavy use, etc.

No one is going to die from using an antique cup once a year for a special tea ceremony.

But i stay away from antique and pseudo antique ware for daily use.

The problem is also that a lot of the kilns are old and not serviced right, so even if the glaze is ok, there is contamination in the kiln itself, and sometimes, when the manufacturers mix pigments improperly or transport in used and old containers, you get heavy metals.

Lead is very popular in glazes in China because it is the cheapest, simplest flux. Glass ( for the sake of simplicity, Silica ) melts at very high temperature, so you need to add flux to help it melt in the kiln.

Lead is a traditional flux used for thousands of years, it is the best, cheapest flux, very easy to use.

Only way to make lead glazes safe is with proper mixing, firing and testing.
That is expensive...

I love using lead in my glazes, especially raku, but because of health concerns, I stopped using it 20 years ago.

[William]

Could be useful to people who want to use old porcelain pieces (e.g. cups or teapots), to read this post from page 1.

Porcelain itself is fired to a high temperature...... around 1300 C. Lead as a flux on silica is not really useful at that temperature; it volatilizes out of the glaze melt and goes out with the gases escaping from the kiln.

The place you CAN find lead however is in the colorful overglaze enamels that are sometimes added in separate lower temperature firings. Those traditional overglaze enamels are a highly lead fluxed composition and are fired so low as to be very unstable for the leaching of lead from the fired surface.

On the flip side, the usual amount of the surface actually COVERED by overglaze enamels is usually small. So the amount of glaze surface available to leach lead is small.

So if you are talking about a plain porcelain piece.... it is perfectly safe. With overglaze on it, if it is a TINY amount painted on the inside on the liquid contact surface... your are probably OK (but no guarantees). If it is a large amount of overglaze inside,.... take a pass on that one.

best,

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

[.m.]

I was very happy to read the above post of John a couple of days ago when Bok linked to it in another thread. It affirms what i've been thinking, but wasn't able to express it, lacking any knowledge of the matter.

[BW85]

Could be useful to people who want to use old porcelain pieces (e.g. cups or teapots), to read this post from page 1.

Porcelain itself is fired to a high temperature...... around 1300 C. Lead as a flux on silica is not really useful at that temperature; it volatilizes out of the glaze melt and goes out with the gases escaping from the kiln.

The place you CAN find lead however is in the colorful overglaze enamels that are sometimes added in separate lower temperature firings. Those traditional overglaze enamels are a highly lead fluxed composition and are fired so low as to be very unstable for the leaching of lead from the fired surface.

On the flip side, the usual amount of the surface actually COVERED by overglaze enamels is usually small. So the amount of glaze surface available to leach lead is small.

So if you are talking about a plain porcelain piece.... it is perfectly safe. With overglaze on it, if it is a TINY amount painted on the inside on the liquid contact surface... your are probably OK (but no guarantees). If it is a large amount of overglaze inside,.... take a pass on that one.

best,

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

So happy all my Qing cups are plain porcelain or blue underglaze only, no overglaze. It's good to know to watch out for that though

[JBaymore]

William,

Thanks for appending "the great" up there in your re-posting above of my comments,..... but it is not warranted. I just happen to be a college professor who has been teaching glaze and clay chemistry and ceramic toxicology for a long time now (since 70's). Over the years I've amassed some knowledge for professional reasons. There are others who are also in that same situation..... who have as good or more of a background than I.

In this discussion of the potential dangers of lead in glazes, one must keep in mind the toxicological principles of intensity, duration, and frequency when it comes to possible exposures. There are no "one size fits all" answers when it comes to this complex stuff. To know what to recommend (other than the general always correctly safe "extreme caution") ... one has to have a lot of information about the situation / circumstances. Diagnosing from afar..... difficult.

Each of us has have to decide for ourselves the answer to the question, "Is something safe unless it is proven not safe?" The answers to that fits how cautious you are in your life in general. That answer is right for YOU.

I'm not an advocate of 'sealing ourselves in baggies" or "hysteria". But in assessing the situation from having good accurate information. Are there valid concerns? Yes. Do some people over-react? Yes.

I have found over the years that studio potters themselves tend to be more concerned with this aspect of their craft,....and the impact on their wares... than maybe people who use OTHER materials for food and beverage. There are a lot of concerns about plastics and the like... that people seem to just ignore.

As a side note... since lead seems to be the main concern here at the moment....... traditional Japanese Aka (red) Raku and also Kuro (black) both have lead as a component of the glazes. Even today, my friends in Japan still use lead compounds. So I'd predict that most contemporary Raku-fired Chawan people here might buy from Japan are likely lead glazed.

If you drink matcha out of them after a good washing with warm water prior to use, (similar to Japanese Chanoyu practice) then the amount of lead that might get into the tea is likely VERY minimal, if any. The amount of surface contact with the form is small, the ph and temperature of the leachate is not all that extreme, and the duration of that contact is quite short.

Additionally, the more any lead glazed piece is used and washed off... the lead release amount steadily decreases........ in some cases almost exponentially. The main lead content available TO leach is at or near the surface of the glaze. As that surface amount leaches out..... it is harder for the underlying material to get "access" to the material causing the leaching (in this case... tea). This concept is true of other potential toxins in glazes also.

As another note....... the Aka Raku and Kuro Raku Chawan that I make do not use a lead based glaze. Unfortunately, this trades off some visual characteristics from the traditional wares. (The price I pay.)

best,

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

best,

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