Definitions of Food Safe

There are certainly legal standards set in both the European Union and the USA which require tableware to pass extraction tests for both lead and cadmium. I'm only familar with the EU position, and it's possible that USA may also cover other elements.

The tests are based on the use of 4% acetic acid as the extraction medium - the exact method to be used will be laid down in an EN or ASTM standard, which will lay down the sample preparation, quantity of acid to be used in terms of the type and volume / surface area of the plate / bowl etc, as well as the extraction time and temperature.

Levels of heavy metals which have been extracted from the article into the acetic acid are then determined using a suitably-sensitive analysis method - general atomic absorption spectrophotometry or I|CP and the result expressed generally in mg/litre or converted to mg/dm2 of surface area. These can them be compared with the relevant legal limit.

As you can see, it's quite complicated and certainly not something which can be carried out without a proper laboratory.

I have seen information on "spot test" kits which are sold in America which rely on a colourimetric reaction of heavy metals with a compplicated organic reagent normally known as dithizone. I very much doubt the reliability of these test kits, as dithizone gives colours with many heavy metals and other common ions block the colour formation.

Of course, if you intend to take this matter further, you should become fully familiar with all the relevant legal requirements - for instance, I believe that California has specific extra (different ?) requirements as a result of Proposition 65.

Regards,

Phil

This to me is a question that is not easily to answered. John Hesselberth and Ron Roy have touched on it in their book and conclude that rather than talk about the issue in terms of "food safe" instead ""safe to use with food provided the clay/glaze fit issues ... are also addressed" (not to put words in their mouth but that the glaze does not shiver or craze (so it does not would allow bacteria or mold to grow). Copper easily leaches out of glazes. Their Spearmint has leaching of copper at 1.63mg/l. They treat this as a glaze safe to use for functional ware but they do not call it food safe. I highly recommend Mastering Cone 6 by Hesselberth and Roy if you do not have it.

I use copper bowls to beat my egg whites. I most certainly get more copper out of that than I would out of almost any copper glaze I have ever used however if the glaze is leaching a great deal of copper you have to ask yourself do you really want the taste of food tainted with metal whether it is dangerous our not. And then there is the issue of the glaze itself losing it's beauty. You want a stable glaze for safety, for function and for beauty.

If you want to be ridged about it and error on the side of safely then you would not use a glaze on the inside of any piece which could hold food that has lead, cadmium, barium, cobalt, copper (heavy metals) in it and that fits the clay perfectly. In other words a liner glaze of white, clear or brown....

John and Ron suggest using EPA standards for water (note that cobalt, copper and lithium are not listed by the EPA).

Copper is an essential nutrient that is become less available in our modern food because it is being leached out of our soil by pesticides and fertilizers. Amounts released by well made glazes are less than dietary requirements.

The original concerns about copper was related to lead glazes where poorly formulated copper glazes helps lead be more soluble.

In India, the switch from copper and brass water containers for plastic is causing problems with water safety. Plastic contained water depends upon sunlight to keep it from going foul.

-- Lee in Minneapolis.

Thanks for the contributions thus far.

Do studio potters in California test their work? Would it be only pieces with say Cobalt in the glaze, one piece per batch?

I find a there's a lot of truth and rumour about glaze safety. I don't know if many studio potters test at all and how many of those test with other than simple kits. I know some who take a glaze from the glaze book mentioned above, a glaze with cobalt, noted with a low leaching rate and then consider the glaze safe even when a differant feldspar is used. I've known some who used lemon juice to visually check for leaching.

I do find that potters are in some ways expected to have higher standards than plastics. Now there is a big variance in concern and knowledge about glazes. I know some ( one ) who are very concerned about crazing and test pieces with repeated heating and freezing. There is concern over crazing even if no toxic materials are imvolved, as bacteria could grow in the cracks. That's a lot of concern considering that many/most people store food in plastic that is easily scratched and there's little concern about build up of bacteria there. I've also noticed some plastic companies warning about heating food in plastic storage containers. But it's widely done and I havn't seen a recall of plastic containers. Let's face it, if overheated the plastics melt down. They are created by huge companies and the studio potters are very small. Of course, a single potter is a lot easier to sue than a big petrochemical corporation. Do any of you know of rules of thumb for glazes e.g.: no more than 5%, 3% copper; no more than 1% cobalt; toxic material okay if under clear glaze. Do you know of any glaze myths?

Do you have categories of food safe such as: table safe, safe for dry foods only, microwave safe, safe for storage of acid items like salads?

( Safety for oven or microwave concerns the clay body as much or more than the glaze.)

Are the big manufacturers of "good china" still using lead glazes? ( in factory conditions with safety confirmed by testing )

Still curious and welcoming imput,

Elaine

This is nice to know and I have read it before - I believe one of the issues with copper in a glaze is that it is one of the ingredients that leaches very readily so if you are not getting significant amounts of copper leaching from your pots that have a high amount of copper in the glaze (4%>) then you can feel secure that the base glaze is stable. However, what is 'significant' The question being posed here is what are the limits of leaching for a standard of 'food safe'. As I said I don't think there is any consensus on what is 'food safe'.

I believe the only standards in this regard that you find listed in this country (U.S.A.) are for Lead and Cadmium (if I did not mention that... bad on my part).

If you leave a lem>

This is nice to know and I have read it before - I believe one of the issues with copper in a glaze is that it is one of the ingredients that leaches very readily so if you are not getting significant amounts of copper leaching from your pots that have a high amount of copper in the glaze (4%>) then you can feel secure that the base glaze is stable. However, what is 'significant' The question being posed here is what are the limits of leaching for a standard of 'food safe'. As I said I don't think there is any consensus on what is 'food safe'.

I believe the only standards in this regard that you find listed in this country (U.S.A.) are for Lead and Cadmium (if I did not mention that... bad on my part).

If you leave a lem>

This is nice to know and I have read it before - I believe one of the issues with copper in a glaze is that it is one of the ingredients that leaches very readily so if you are not getting significant amounts of copper leaching from your pots that have a high amount of copper in the glaze (4%>) then you can feel secure that the base glaze is stable. However, what is 'significant' The question being posed here is what are the limits of leaching for a standard of 'food safe'. As I said I don't think there is any consensus on what is 'food safe'.

I believe the only standards in this regard that you find listed in this country (U.S.A.) are for Lead and Cadmium (if I did not mention that... bad on my part).

If you leave a lem>

Yes, I've gotten that impression.

Yes. And glass and ceramic have an advantage, in smell alone if not taste, over some plastic and metal mugs that I have. While low tech that lemon slice text sure is handy.

At one time I used to leave a plastic glass by my bedside. I no longer leave a glass out but I gather I used plastic for its unbreakability. The water had a bad taste by - the morning? next evening? At first I blamed the water supply but then I realized it was the plastic "glass" itself that was flavouring the water. I've seen a lot of talk recently about which plastics, identified by recycling number, are safe to use for storage ( once emptied of their original contents).

I know a potter who went to Ghana with an aid agency. He found, that in that area, unglazed eathernware was great for water storage. Water loss due to porosity wasn't that great and the evaporation on the pots' surface kept the water distincly cooler than air temperature.

Elaine

We are having what I some times consider 'overkill' going on in our studio over the issue of 'food safe' and material safety. Pinnell's Weathering Bronze green, which to me is a wonderful glaze, was eliminated as a glaze we could use because it became known as 'not food safe'. This is a glaze that a great many potters firing at cone 6 (and higher) use. The environmental safety crew took away our Nytal Talc because after ten years of lawsuits in the state about this talc's safety with no conclusion someone in the University's administration decided that this talc was the same as asbestos (it isn't). I can tell you that this caused all sorts of havoc since the replacement talc did not have the same chemical analysis as the Nytal and 5 of our 10 glazes changed not in a good way. Reformulating seems to have worked for the most part but anytime the glaze misbehaves you wonder - does it still need some tweaking?

I can't complain too loudly really because good things came from this. I went from having to make up a glaze in a room where I had to dodge students and worry about them being exposed to dust to having a room just for making glazes that has a really good venting system. I can understand in a studio situation where there are too many cooks and students to monitor, wanting to limit glazes to only ones that are good for functional pottery but if you take this to extremes you only have glazes that go from white (possibly clear if you can find one that doesn't craze) to brown. If you try to have glazes only meant for sculptures, you can tell everyone that "this glaze is not food safe - only for sculptures!" and you can be guaranteed that someone is going to ignore the warning, glaze a bunch of dinnerware with it, decide they don't want it and then sell it at the next studio pottery sale. Having glazes that are 'food safe' would be nice. The problem is that no one knows what this is. The decisions about the glazes seem arbitrary and without any rhyme or reason which of course makes people dissatisfied.

Oh! and P.S. I refuse to drink water out of the refrigerator water supply anymore because it taste yucky and I think it is from the new plastic filter it goes through. I would rather go without even good wine than drink it from a plastic or paper container. I would rather have far, far less with quality than otherwise. Less is more - and the older I get the more meaning this has.

There I have had my rant. I must say though that I do miss the bliss of ignorance some times.

Donna