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canyon fox

food safe?

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Hi, I'm trying to find out if the glaze is food safe.

It contains a lot of manganese oxide, which i was told by experienced potter is a poison and shouldn't be used inside of dinnerware.

Some other people told it's safe, but wouldn't give me any detail to convince.

 

The Recipe:

Manganese Oxide 66

Copper carbonate 17

Ball Clay 17

Fired to cone 5-6

 

 

Please give as much detail as you can with your answer.

 

Thank you!

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It depends on whether or not it leaches, how much, and how quickly.

 

Here is a thread on this subject from this site

 

And some links on the subject from Digitalfire

 

Is Your Fired Ware Safe?

 

Are Your Glazes Food Safe or are They Leachable?

 

Who are the "other people" who said it was safe and why did you find them to be unconvincing?

 

Ti Phillips

Earth Stoke 'N Fire Pottery Studio, who answers at ALLEXPERTS site, but she wouldn't give any explanation on why she thinks it's safe.

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Both the manganese oxide and copper carbonate levels are extreme; are you sure this is a glaze and not an oxide wash that you would put a clear glaze over? Don't think it would pass a "food safe" test.

 

I use it as a glaze.

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i think that in a glaze like this, where it is made up of such large percentages of toxic materials, you would have to assume it is unsafe until you can convincingly demonstrate otherwise. you could get it tested professionally to see how much it does leach (it's definitely going to have some leaching), but as far as i know there are no industry standards for manganese leaching. in that case you'd have to compare the results with the standards for contamination in drinking water, or with the standards of the leaching of other metals in pottery that do exist (lead, cadmium). in either case its far from an exact science, so it would be nearly impossible to demonstrate that this glaze is safe.

 

personally, i would never use it on food surfaces, because i don't think any test could convince me it's not a potential hazard, and i would think twice about even having it in my studio. in fact, i think it would be extremely irresponsible and dangerous to use this on a food surface.

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i think that in a glaze like this, where it is made up of such large percentages of toxic materials, you would have to assume it is unsafe until you can convincingly demonstrate otherwise. you could get it tested professionally to see how much it does leach (it's definitely going to have some leaching), but as far as i know there are no industry standards for manganese leaching. in that case you'd have to compare the results with the standards for contamination in drinking water, or with the standards of the leaching of other metals in pottery that do exist (lead, cadmium). in either case its far from an exact science, so it would be nearly impossible to demonstrate that this glaze is safe.

 

personally, i would never use it on food surfaces, because i don't think any test could convince me it's not a potential hazard, and i would think twice about even having it in my studio. in fact, i think it would be extremely irresponsible and dangerous to use this on a food surface.

 

 

I go along with you here, as I do not like anything as toxic as that in my studio. I use all of the ingredients. in such minute amounts that they are negligible in a glaze. At the same time I stay away from glazes having high toxic chemical amounts, Barium glazes being one.

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I do not have to look at this recipe for more than 1/10 of a second to analyze the basics of what it actually is.

 

That is NOT a glaze by any stretch of the imagaination. It might be classified as somthing like an "oxide wash" as was correctly pointed out by biskepottery in the post below.

 

There is no glass AT ALL that will develop at that cone range to tie up the metallic oxides into any kind of matrix. If the oxides are not held into a glass........ they are just sitting on the surface. Since manganese is pretty toxic upon ingestion....... this is not something to put on a food bearing surface for sure. Copper too is not great in high doses... and for certain people with a specific disease... it can be fatal.

 

To have a glassy matrix to disolve the colorant oxides into you would need to melt the ball clay; it is the only thing there with any glassformer in it (SiO2). At cone 5-6, ball clay... ANY ball clay... is FAR from being melted into a glass. You'd likely have to go to about cone 30 to do that.

 

The ball clay is there mainly for improving the brushing consistency of the oxide stain from just using straight oxides.

 

This wash, if put on thickly even with a good clear glaze over or under, would likely STILL deserve a leaching test.

 

best,

 

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

mregecko likes this

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Glaze and I don't really get along, so I know less than I probably should about them, but this recipe for a "Glaze" looked suspicious even to me.

Because I have been looking at recipes for black slip lately, I thought that this more closely resembled a slip recipe, but that still seems to be a MONSTER amount of Mn for a slip or glaze, alot of them have 4-6% Mn.

Then I was wondering where the glass formers were, I thought "there can't be enough in the ball clay, can there?"

So I'm glad bciske and John weighed in on this, I at least learned something. Now to get to that pound of MnO2that I have out in the studio...

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we had a "glaze" similar to this - it was called manganese lustre - when i went to school at nscad. it was dark, irredscent and textured - not to mention beautiful. i used it quite a lot on my sculptural pieces at the time, but even being the naive student i was then i sought out other glazes with similar properties that had less toxins in them.

 

before i go any further just let me say that i am not disputing that the glaze is a hazard - it absolutely is. but, just for fun i will dispute your assertions that it is not in fact a glaze. you see, when i used this manganese lustre i used it like a glaze. i dipped my bisqueware into a big bucket of it and it came out looking like a glaze. i had to be extremely careful with the thickness, because anything over a certain thickness would run like the dickens. i've seen others use a pure manganese dioxide wash on bisqueware, and it doesn't get shiny or runny quite like the manganese lustre glaze.

 

forgive my back-of-the-napkin calculation here (i don't have my glaze calculation software on this computer), but i think the formula for this glaze might be something like...

MnO2 0.80

CuO 0.20

Al2O3 0.10

SiO2 0.20

...if one assumes the manganese and copper can fall into the role of fluxes. this material certainly acts like a glaze, it gets shiny and melty, and i don't think those properties are a result of the material reducing to a metallic state because the glaze works just as well in an oxidation kiln. so it seems to fit the glaze/glass definitely of an amorphous solid. i would guess that the copper and/or manganese oxides are actually also fulfilling some of the role of the glass former in this glaze, not unlike, for instance, a glaze that might be made up from 20% silica and 80% boron oxide.

 

in any case, a glaze that contains such low levels of silica in the formula couldn't possibly be durable (insoluble) enough for food surfaces, and the fact that the bulk of the glaze is made up of really toxic stuff ensures that plenty of those toxins will get into any food that comes into contact with it.

 

that enough detail for you?

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This is not a glaze or a slip.  It is a colorant wash.  Much as when you use Iron wash on a body, it might react with the body and possibly lower the melting point of the clay causing a metalic sheen but it in no way qualifies under any definition as a glaze or even a slip. 

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The ONLY oxides legally regulated in the USA by the FDA for food usage are lead and cadmium compounds. So if you read Amaco's website data on what they mean by this particular claim, they look like they are playing that technicality. Notice also the statement about testing yourself (using the word "MUST"). There is NO indemnification to the end user for usage of commercial clay and glazes from ANY supplier .

 

We don't have their proprietary recipe or molecular formula fro the glaze you mention, so even though visualy similar.... MAYBE it is actually OK. To assume anything else is inappropriate. There is no standard for manganese relaeas by the FDA..... and that is the yardstick they seem to mostly use.

 

They do have glazes that they decide to label as not dinnerware safe, but the standards they use are purely a personal set of guidelines since other than lead and cadmium,... the FDA does not care ..... and Amaco does not articulate them other than to say "soft" or "crackle". "Soft" has little actual technical meaning.

 

All their dinnerware safe status claims is one specific thing: "Dinnerware Safe glazes contain no lead or raw cadmium bearing ingredients." It dioes not say anything else is implied.

 

Anyone want to cough up the $60-ish dollars it'd take to have the Amaco glaze lab leach tested for manganese release and comparison to the US drinking water standards (the best guess to use, lacking any real standards)?

 

Know your materials, folks.

 

best,

 

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

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The question of food safety is one issue. The other is the hazard of the fumes to the potter during the firing. 

Toxicity of a material varies by the method and degree of exposure. Some metals are micro nutrients or

beneficial for certain uses, but breathing the fumes is hazardous. Zinc falls into this category. I'm wary

of manganese for this reason. I don't believe it's ever been proven to be linked to neurological problems,

but I also don't think it's been throughly researched. There have been some suspicious health problems

with potters using a lot of manganese.

 

Ruth

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The results of using some toxic chemicals give awesome results but I have a list of safety directives on pottery chemicals that states manganese could cause Parkinson's disease in it's powdered state. That alone keeps it out of my studio & a good warning to newbies to make sure what they are using & how they are using those chemicals. Respiratory diseases are not something anyone wants.

 

You also want to be sure you are not poisoning your family, friends or customers.

J

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I'm wary of manganese for this reason. I don't believe it's ever been proven to be linked to neurological problems,

but I also don't think it's been throughly researched. There have been some suspicious health problems

with potters using a lot of manganese.

 

BACKGROUND:  I teach ceramic toxicology in my college's program, was also the overall school's Health and Safety Coordinator for a while, and the chair of the health and Safety Committee for about 7 years.  Got involved in the whole H+S thing WAY back in the mid  70's when I was working for MassArt and on the H+S Committee there. 

 

You are right to "suspect" manganese compounds.  Manganese is pretty well known to have some significant nurological issues.  There are lots of others less well known too..... for some reason we must believe that anything that can create a beautiful blue must be harmless... but check out the information on cobalt compounds ;) .  No one ever seems to mention cobalt.  And lots of copper leaching from a glaze can kill someone with Wilson's Disease.

 

Every ceramics major student in our college's program goes through many hours of very direct instructional information on this subject alone as a part of the ceramic chemistry course.

 

Here's the opening introduction section from one of my toxicology class handouts that deals with studio practices:

 

-----------------------------------------

Introduction

 

Like utilizing any artistic medium, the activity of producing ceramics exposes the artist to the potential effects of the materials which are employed.  In most cases, some educated common sense will go a long way to minimizing these hazards.  In my opinion, having a good understanding of the potentially toxic properties of what you use, understanding how various processes can produce hazards, and understanding appropriate workplace standards is a fundamental part of the educational process for any artist.  What you don’t know can hurt you.  

 

Unfortunately, there is little relevant data on this subject from which to draw.  Most full-time studio artists are in the studio much more than the standard "industrial measure" of 8 hours a day for 40 hours per week that is used in occupational health studies. Part-time ceramists also often spend long, intensive weekends and occasional entire vacation periods at dedicated work.  Therefore, these few health studies which do cover the materials we tend to use are not necessarily directly applicable to studio potters.  If your studio is located in your living space, the contact with some materials, particularly airborne dusts, can be as great as 24 hours per day.  These same hazards are also of consequence to the artist’s spouse, children, friends, and pets if they share the combination living/studio space, or if the artist regularly wears very dirty clothes and shoes into the home. 

 

Here in the USA, employees working in the artist's studio are another specific, specialized category, and are covered by very specific OSHA laws with which any employer is required to comply.  If you have employees, consult your legal counsel, business advisor, and the local OSHA office as to the appropriate steps to take.

 

note - ©1997   J. Baymore    -all rights reserved

------------------------------------------

 

I post this following reference a lot here on the forums when the whole "toxicity" and "food safety" thing comes up. 

 

Reference books / handouts that every ceramic artist really should have in their library:

 

"Artist Beware"

Dr. Michael McCann

Lyons Press

2nd Ed.  1993  576p 

ISBN 1558211756

 

"Artist's Health and Safety Guide"

Monona Rossol; Industrial Hygienist

Allworth Press

2nd Ed.  1994  343p

ISBN  1880559188

 

"Keeping Claywork Safe and Legal"

Monona Rossol; Industrial Hygienist

NCECA Publications

PO Box 1677

Bandon, OR  97411

800-99NCECA

 

 

RESOURCES

 

ACTS (Art, Crafts, and Theatre Safety)

Monona Rossol; Industrial Hygienist

181 Thompson St., # 23

New York, NY 10012-2586  

(212) 777-0062

 

>>>>Subscribe to the newsletter "ACTS Facts"

 

OSHA Publications Office

200 Constitution Ave., NW

Washington, DC  20210

(202) 523-9667

 

 

 

best,

 

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

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Interesting read this thread. I don't really have much understanding of this. When the oxide is in a glass does this mean it is safer than just on the surface? Is it just trapped in the glass or fused into the structure?

 

Is there any difference in toxicity between manganese dioxide/oxide?

 

I recently purchased some manganese dioxide but have been hesitant in using it.

 

I do use a glaze with cobalt and copper in so now you have got me thinking!  :blink:

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