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Lead Glaze Recipes (No Safety Lectures Please)

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Tim,

 

Your position on lead is about 60 years obsolete.  Unless you're glazing with fused quartz, your glass is leaching. Well-formed glazes and "good glass" as a defence against leaching are illusory concepts and simply do not exist.  Even lab grad boro-silicate leaches.

 

 This is why there are dinnerware limits set.  The problem with leaching is that it's not exactly a consistent problem.  My dad has a set of dinnerware I wish he wouldn't use.  I think it was a gift.  Lovely Yellow and Orange set.  It has lead in the glaze..  He got it like 10 years ago.  Well after the lead regulations came down here.  Despite meeting the glaze requirements at the time of manufacture, the surface of the glaze has become heavily degraded and definitely has leached a lot of nasties into the food he eats.  Just because it's good glass one year, doesn't mean it's good for a lifetime.  I believe this is a pretty well observed and talked about phenomenon, as well.

 

And this is one of three problems.   Another is that, you may have a neat unity formula that looks like it will make a durable glass, but if you don't fire it properly, it won't matter. This is what Neil's talking about with testing.    And kilns have cold spots and hot spots.  So even though you get plate 1 tested, plates 3-5 don't have teh same level of vitrification and slip by anyway.  Not to mention that elements and circuitry degrade and kilns fire differently over time.  It's impractical for the artist potter, studio potter, or even small and medium scale production potters to test for lead.

 

This issue is also why the assertion that lead frit has no effect on the safety of the glaze, is fallacious  This assumes alot.  1)  it assumes the glaze you're putting it into is well-formulated.  If the frit's good, but the glaze is bad, the frit's virtues are nil in the final product.  2) it assumes proper firing.  Over fire, for instance, and you could be poisoning yourself.  3)  it assumes no prior errors.  Lead contaminates your kiln for years.  If you've ever made a mistake with the stuff, it's in there still, contaminating everything you put in there.  This is where a lot of contamination can come.  Lead's fugitive and likes to vaporize.  Even at low temperatures (like the melting point of metallic lead), it could be poisoning you the potter and contaminating the kiln.  Just because the user may not have any worry about the safety of manganese in a glaze or clay body, doesn't mean the potter shouldn't be worried about the dangers of exposure during firing and application.

 

Again, do your research, your position's obsolete.  it may be true that there are no perceivable ill effects, but there are always ill effects.  The modern consensus is that there is no safe level at which lead can be consumed, the only reason why it's still around is that it's so industrially useful.  Cars run better and last longer on leaded gas.  Lead paint is more archival than the alternatives.

 

And think of your position from the position of "cui bono?"  Whom does it benefit to say that lead is safe?  Not the potter who has the bear the brunt of the risk.  Not the consumer who could be betrayed by the potter's error in judgment or greed.

 

As for the link between lead and criminality.  I would have been right there with you if it weren't such a studied phenomenon.  Hit up Google scholar and see what you can find.  The demise of lead in gasoline as linked to a decrease in violent crime after the 1990s, is one course of research.  The poverty angle is one.  I realize you're in the UK, so this may not be something you're familiar with, but have you see Fat Albert and the Cosby kids?  Mushmouth has lead poisoning.  His character's personality and behaviour is consistent with the symptoms of chronic lead poisoning.  And talk to anyone who lived in poor areas before the 1990s, they knew a Mushmouth.  There was an article written on this, and how Fat Albert depicted a lot of the issues faced in poorer areas.  Russell wearing a coat, scarf, and hat was indicative of a common untreated illness.  So while poverty is a factor (in the sense that impoverished houses are more likely to have lead pipes), the symptoms of lead poisoning are never far from sight in the research.

 

I feel the most important thing to take away from this exchange is to ask yourself "why are you arguing for the safety of lead?"  Aside from the fact that it makes a prettier glaze, there's no reason for any small scale operation to use lead in any form for functional ware.  Literally no level of lead is safe, but we put up with it because our existence, to a great extent, depends on it--loads of industrial applications require lead, but ceramics is no longer one of those applications.  If you want to make awesome art pieces with it, that's one thing, but i has no place at all in functional ware.

 

A functional-ware potter arguing for the safety of lead is like a coke addict arguing for the safety of cocaine.  In some context,"I'm really really careful" and "it's just a little bit" or "only at parties"  could be valid arguments, but as it stands, the only reason the user has for saying them is to prolong use.  And from what we know about both, prolonged use only prolongs risk.

 

 

Tyler,

No probblem picking out my post, I'm happy to have an inteeligent debate.

The reason lead hasn't been banned from dinnerware glazes is that if the glaze is well formed, there is no health hazard to the user.

The problem with lead glazes is the hoby/craft sector, most of whose practioners don't have access to the knowledge of glaze chemistry that industry does, who tinker with glaze recipes without fully understanding the issues in making a safe, well formed glaze.

I, and most other readers here, probably do eat our fruit salad out of lead glazed bowls, with no ill effects.

FYI, using a lead frit has no effect on the safety or otherwise of the final glaze, it only protects the potter from lead poisoning when making up and applying the glaze.

As for lead pipes, one has to be careful with statements like this - lead pipes are more likely to be found in older houses that haven't been refurbished (it was banned in Europe in 1970 for new builds), so the properties with lead pipe are more likely to be owned by poorer people, and poverty has been shown to be the biggest predictor of life satisfaction scores, so is it poverty or lead piping that is at fault?

Tim

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Tyler,

We'll have to agree to differ on this.

Of course certain assumptions have to be made - following your argument, even leaving lead aside, if you use many of the glaze materials (manganese, vanadium, barium, ...) and misfire it, one will risk poisoning the user. Perhaps all of these should be excluded from functional ware as well? On the lead side, you obviously need to destroy any crystal glass you may own, and switch to eating off wooden or plastic plates in case your dinnerware has a lead glaze and was misfired (which can both contain toxins, by the way). Over here in Europe, lead in gas and paint has long been banned, though it is still allowed in glazes - but if still allowed in Canada you need to emigrate.

Less flippantly, yes, I agree testing is needed for glazes used on parts of functional ware exposed to food. This starts with using the rules/formulae that are in several of the journals as guides to a safe glaze, and is then followed up by testing. By a well formed glaze I meant one that was not only well formulated, but also properly fired.

I'm not sure why, but caution about lead seems to be stroner on N America than in Europe.

Tim

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Perhaps all of these should be excluded from functional ware as well? 

 

Tim,  this.

 

You'll notice that a lot of people use no seriously toxic ingredients in their functional glazes.  Why bother with the liability and risk for ourselves as potters and for our consumers?    As I said, all glazes leach.  Glazes within the usual limits leach minimally, but they still leach.  So why bother?  I'm not too worried about the leaching sodium and potassium of a cone 10 celadon.  I'm not too worried if a tenmoku leaches a little iron.  Even a little copper is acceptable--I'm not allergic.  There could be a visible crust of borates on a piece, and it still wouldn't be that bad.  To put my money where my mouth is, I've not used anything more toxic than small amounts of cobalt in my glazes for about 3-4 years.  I just don't believe in it, for me in the studio or for my intended users.  In fact, I'd kinda like guidelines about leaching for more than just lead and cadmium.  

 

Lead crystal is, btw, indeed a bad idea.  White wine stored in a crystal decanter for an hour (the length of a meal, say), doubles its lead content.  Port wine stored in a decanter for four months (some people do this), will have a lead level of 2,000-5000 µg/L.  Brandy stored long term in crystal can get as bad as 20 000 µg/L.  Compare that to the levels Neil cited above.  The only thing that saves lead crystal is that most people don't use it this way, and the exposure and leaching is limited to that which happens through immediate use. l  Much like the Japanese justification for lead glazes in raku, despite being more or less verboten elsewhere in Japanese ceramics.  But people are idiots, and certain level of idiocy is to be expect.  People use raku chawan for soup, so why wouldn't they hold fruit salad in lead crystal for a few hours before the party?  Why not store the leftover ones in the crystal too?  

 

But really, why should anyone be so stuck on using something that can be made in a non-toxic way, and has been made that way since before the Romans?

 

Again, I ask, cui bono?  For what good would anyone commit themselves to using lead?

 

Tyler

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The mindset in the U.S. is that if it contains any trace of lead, customers will walk away from the item. And, one of their first questions will be, Is the glaze lead-free. Even though there are permissible levels of lead allowed, even though you might only put it on non-functional wares or non-food surfaces, even if the lead is encapsulated or fritted -- if it has lead in it, customers will walk away. It is that simple. They know to ask about lead, maybe not to ask about barium, manganese, and a few others.

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I get asked about lead and food safety at every show I do. The dangers of lead are something that everyone is aware of, and something that is relatively easy to deal with- you just don't use things with lead in them, starting with your dishes. I guarantee that if I had glazes with lead in them, and I made every potential customer aware of that fact, I would sell little to nothing. It's just not worth the risk when the next 1,000 potters have beautiful glazes that don't have lead in them. In 23 years of making pots I have never yearned for using lead in my glazes. There are just too many other great options available to make lead use worthwhile.

 

Barium, Vanadium, Manganese- I don't keep these in my studio, either. I'm not going to risk my health, my student's health, or our customer's health by having these in our glazes. I explain this to my students all the time when they ask for a barium turquoise matt, and once they understand the health risks they are happy that I am looking out for their safety.

 

I don't think there's a single good reason for using lead in dinnerware. "Beautiful" doesn't cut it.

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As an art teacher starting their career in early 70's, the presence of lead, uranium, and other materials we wouldn't think of is ghastly! Copper enamels used abundant amounts of uranium for colors as well as lead and other heavy metal compounds. Glow in the dark type stuff, at least with a Geiger counter.  We had lead in glazes even though they were marked not food safe, and paints and other materials were suspect. Over the years, awareness/knowledge, cleanup, and disposal was something we had to do on our own. As soon as we started getting warning documents or articles in trade journals it was back to the stockrooms to find out if we had anything in the current scares. 

 

Years later some of that still stays with me, as many of you have read some of my feelings about materials. Chilling to have the beast brought out of the closet again, but I look at these sorts of discussions in the realm of academia enlightening, and the knowledge exposure is important to newbies, and others pursuing involvement in the arts and crafts. 

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I was under the impression that Zinc Oxide probably contains Lead impurities, so if using Zinc can you really say work is Lead free? Probably so little that it makes no difference.

 

Yes, lead can be found with other materials, but like you said it's typically in very small percentages. When I was in charge of safety labeling for the clay and glazes at the ceramics supply company that I used to work for, I would regularly have to send certain raw materials off to the lab to have them tested for lead. Lead is the primary thing they are looking for in certifying clay bodies as non-toxic. Glaze certification is a little more complicated since they get into metallic oxides, but lead is on the list for sure. I specifically remember sending out samples of copper and cobalt to be tested for lead.

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Hallo everyone,

 

I thought what a relavant information and discusion will be on this forum.

Althrogh a founder pleads "No safety lectures please" it degenerated to toxophiobic forum against lead glazes...

 

Stop it please...

 

EVERYBODY from ceramic comunity knows what lead is poison and it should be used lead glaze carefully.

But, i thing, what a lead glazes have own place in ceramic art, and it is possible to use it safely in low-fire technology without greater risk.

 

Lead glazes is fantastic!

We use it in our decorative pottery many years. We returned to them after long term using of lead-free glazes :-)

In contrast to US in Czech rep. they are not so prohibited.

Mainly we use comercial glazes from Glazura Roudnice factory, tradiltional czech glaze producer, which have very good color palette of lead glaze.

see www.glazura.cz

 

It was some question about lead chromate glaze previously. They produce glaze Lu64791. Fired to 960°C (on horizontal surfaces, as it si very liquid!) form intensive chromate red with long needle crystal of lead chromate :-)

 

And also uranium lead glaze is also very good (its, of course, long term out of Roudnice factory production...)

One of the best tested composition with sodium uranate from old literature (Zimmermann 1928, Sprechsaal) is:

minium 63.9 %, quartz 8.5 %, kaolin 11.1 %, sodium uranate 16.7 %

(Seger formula SiO2 0.8, Al2O3 0.15, PbO 1, + 20 % sodium uranate)

Its simply, but form fantastic fire-red :-)

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People on this forum are very knowledgeable, and have been working in the field of ceramics for many years.

They aren't going to suggest anything, that is dangerous to you, or potential customers.

 

If I came in here asking the best way to run electricity to my kiln from my fuse box, without hiring an electrician, people here wouldn't give me a step by step. They'd advise against it, because odds are, I'd be putting myself at risk.

The same is true in the case of lead glazes.

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Wiki 1,

 

From your site www.glazura.cz re: "G transparent lead glaze: PbO 10 - 60 wt.% Due to such a high lead content are recommended exclusively for the production of decorative ceramics."

 

How on earth does one ensure that these glazes are not used on functional wares? How do you ensure that a decorative piece isn’t used in another manner? Once a piece has left the makers hands they have no control on how it is used. Similarly, once a bag of glaze has left the manufacturer they have no control on how it is used.

 

Yes, lead glazes can be very attractive and as such there are going to be people who will use them on functional pots either out of ignorance or greed.

 

Its not a question of North Americans being toxophobic, it’s a question of science and human nature.

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As far as the user of the product is concerned, the risks are pretty well zero so long as it is a well developed glaze and, in the case of lead, has no copper in it. I don't believe there is a single record of a death of someone using ceramics with a lead glaze due to lead poisoning.

 

We didn't give any safety lectures to the original poster. In fact, a lot of supportive responses were given. It wasn't until the post above that we got in to the potential dangers of lead use. The purpose of the forum is not just to respond to the person who starts the topic, but also to make sure that anyone who reads the topic in the future is not given false or misleading information that could be dangerous to him/herself or others. There's no way we were going to let that comment lay there untouched.

bciskepottery, JBaymore and Babs like this

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Wiki1,

Look at my original post, you can pick up that book on amazon.co.uk or abebooks.co.uk quite cheaply, and it is by far the best book I have found on glaze colourants, including lead chromate, uranium, and to a lesse extent the rare earths like selenium.

Tim

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Tim T,

 

many thanks for Your commentary, and reasonable wiew, I absolutly agree with You.

(I must to admit that I have not read your first e-mail carefully enough. I was now in the workplace rather sporadically...)

 

You write that you did not answer from czech glasswork supplier. I know a few glassmakers, who told me about the transport of "yellowcake". As surely, as if they had brought in who knows what terrible :-)
I can help you and try to reach the supplier in his native language if he would be willing to send a consignment to You to the UK, and under what conditions. If You are intersted...
 
And also thanks for tip for Kenneth Shaw book! 
But on Amazon and other servers I foud three modification. First is without subtitle, second "with ilustrations" and third with subtitle "Manual for the chemist, techniologist...and students"
They cost is quite different...
...Is it multipart book?
What Yo can recomend me?
 
Thanks :-)
Wiki1

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Hi,

Good to have  a sensible discussion!

It is a single part book, and mine is a hardback. It has photos but they aren't much use because they are black and white (due to the age of the book) and just of people applying glazes etc.

In this link the first 4 are all the same book: http://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&field-keywords=ceramic+colours+and+pottery+decoration+shaw&rh=n%3A266239%2Ck%3Aceramic+colours+and+pottery+decoration+shaw

Thanks for the offer re yellowcake. The web site is http://www.ujp.cz/. Price is also a concern as when looking I also came across a supplier of very high purity material for chemists, which was very expensive and much purer than needed.

If you want, email me on timtwickham at hotmail.co.uk to avoid the health and safety evangelists!

Tim

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Baaah, you little stinker... :D You should give terracotta a chance! ^_^ I mean... redart with mica? It SPARKLES. And it's RED. And it's like buttah.

I have been wanting to look into luster, but I'm chicken and it's suuuu expensive!

-G

I've got a crap load of old earthenware clay, bagged up, rock hard dry that I am going to reconstitute and then fire Majolica. But then those stoneware and porcelain glazes keep sucking me back in. So beautiful...so little time.. so beautiful...[sound fades out].

TJR.

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I am no expert in lead, and I certainly wouldn't put it on any of the functional work that I do.  Its just not worth thinking about from a liability standpoint, and the lawyer in me says "Who knows what some kid would do, even with a sculpture?"  That said, I have read some older ceramics books that contained extensive discussion on using lead in glaze.   At some point I read The Potter's Craft by C.F. Binns, and I recall that he discusses in detail the chemical formulas and differences in red lead and white lead.  I believe he had a variety of recipes for lead glazes. You can get electronic copies through google play. 

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LawPots, lead is still used in many commercial glazes for things like dinnerware, and if properly formulated and fired is perfectly safe. In the hobby/craft ceramics area there are many people who don't have the technical knowledge or access to resources to formulate and test a glaze to ensure its safety.

 

Thinking things over, I must admit I tend to agree with you and others that you can't be too safe. I'm not sure what form of non-functional ware the original poster makes but, for sake of example, let's assume he models pigs. Then some of the following scenarios come to mind which could put people at high risk of lead poisoning:

- if used as the centrepiece of a dinner table with a Heston Blumenthal style menu, the guests may think that instead of creating edible wallpaper the chef has put an edible glaze on the pig, so they reach over the table to lick it

- on a hot summer's day a playful uncle may play hide the ice cream with the kids and, seeing the similarity between pigs' ewars and ice cream cones, fill each ear up with a few scoops of Ben & Jerry's finest, for the kids to find and lick out

- following the lead of our inestimable leader David Cameron in his youth, up and coming young Torys may want to use the pig's mouth to show their dedication to the cause (I'll leave you to Google that one for more details)

- another creative ceramicist may make works out of shards of broken pieces and, coming across the broken pieces of the pig as a result of the erstwhile owner throwing it away because of the risk of lead poisonong, they retrieve it, and include pieces of it in artistic functional looking pieces (that may also include other delights like matt Barium glazes or glass Fiesta ware), which are then used in a functional way

 

I'm sure you'll agree that the possibilities are legion, whatever the piece being made, and all lead should be banned forthwith or at least, like much of our polluting activities, exported out of sight to a poorer country.

 

Tim

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I did a bit of work with lead glaze in the early 1970s.  At one point I talked to an elderly Michael Cardew who I knew had glazed kiln loads by dusting with lead sulphide in his earlier days, and his mind seemed unaffected.  I thought I understood the threat lead presented.  However, when the problem of lead in the water in Flint hit the news I thought I'd research further. 

 

Take a look at this graphic.  It was created by Clair Patterson, the first person to discover how widespread lead in the environment had become due to civilization's careless use of lead.  What he discovered was that human beings in the preindustrial age had almost no lead at all in their bodies, compared to modern humans. 

 

The "low" levels of lead present in our children today, now that we've taken the lead out of gasoline, paint, and plumbing materials, restricted its use in ceramics, etc., are still hundreds of times higher than what your average pre-contact human had.  The problem with this is there is no place for lead in human biology.  It comes into the body and is used as a substitute for calcium in nerve pathways and basically screws up operations. 

 

As the average lead level in humans has declined over the decades as civilization has been more careful in its use, scientists have had an opportunity to study the effects of lead at "lower" levels.  They aren't finding a threshold level below which there are no harmful effects. 

 

The level of lead in Flint kids today is a fraction of the level of lead found in all children when I was a kid, so there are some who say who cares. We all lived through worse.  But the recent discovery is that if you take a population with a "low" lead level such as the average US level in children today and increase it bit, to a level thought mere decades ago to be so low no possible damage could occur, the entire population loses a significant number of I.Q. points.  You end up with far less genius, far more mentally retarded, and a whole population less capable than they otherwise would have been. 

 

Regulators take into account how much its going to cost to further reduce the exposure of humans to lead in the environment as they set limits on what can be used where.  But the long term goal is to reduce the exposure to zero. 

 

So I realize many may not want to hear any "safety lectures", but the thing is, its time to give up the use of lead. 

 

It isn't just the immediate threat posed to you when you use the material in your studio, which can be drastically minimized or eliminated.  It doesn't matter that there is no supposed effect on your client, who can be advised that the glaze has lead in it.  Its the fact someone had to mine it and process it to get it to you, and the fact that your product will eventually have to be disposed of somewhere or will end up somewhere.  There's too much lead dispersed in the environment already. 

 

Civilization has used up its lead quota. 

Min and flowerdry like this

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