Opinions Of Copper Additions

[MMB]

Last year some time I posted a thread about me adding dust and shavings from a hardware stores key maker. I had only fired to ^06 and it turned a typical dinnerware safe clear a deep green.

 

Thats the pic ^^^. So later down the road a few months ago I had some spare time and mixed some into Coyotes ^6 glaze to see what would happen. Results were better looking because I enjoyed the new white that showed up.

 

 

Im not looking into this to really delve deep. This stuff was just free and more of it is free. So why not enjoy some freebies. I know Im more than likely adding a bunch of flux to this glaze and it will just run a bit. But in the interest of formulating my own glaze I could have a chance to cure some of these issues. Like I said Im not making this a full time test, just curious. Although this curiosity leads me to question is adding key shavings (mainly copper or brass or a stitch of nickel) even fired to cone 6 potentially toxic? Ive read that their are some issues but also that there are no issues. Something I come to find a lot in this clay world. Opinions? Hearty discussion?

 

[TJR]

MMB,

I had heard a long time ago that key shavings were a good source of copper. I am wondering if you ground them finer-say in a mortat and pestle, if you could add them directly into a glaze? You are right, it looks like there is some flux in there, or maybe it is the vertical position of the piece. Try some on the inside of a bowl over a white glaze.

I personally like the first example. That is one beautiful colour.

TJR.

[neilestrick]

Copper will flux out a glaze a bit, especially at cone 6. Glazes can only hold so much copper, and then they start to leach when the percentage gets too high. If you look at your first sample you can see where it's getting very matte and dark in places- too much copper for sure. Anything over 5-6% is generally too much. Ultimately you'll have to send it off to a lab for testing, but a good home test to start with is to set a slice of lemon on it overnight and see if it discolors.

[Guest JBaymore]

Well the starting point here is that you have absolutely NO IDEA of exactly WHAT has been ground on that key machine.  The composition of what you are getting is variable and is dependent on the exact ratio of all of the varoius things that the people at the store might be grinding. 

 

Every batch you get will likely be different too.

 

I've seen key blanks with various colored paints on them, I've seen steel looking key blanks, I've seen brass looking key blanks, and I've seen key blanks that could be most anything.

 

I'd keep this stuff on non-functional (non food use) forms.

 

I'd personally move Neils copper content potential concern limit down a bit..... I'd be concerned of any glaze holding more than 4% by weight of copper carbonate and less than that of copper oxide for food contact (due to molecular weight differences for the copper ratio in the raw material). 

 

Even leaching a small amount of copper is HIGHLY toxic to people with Wilson's Disease.  For others... it can affect food taste at the least.

 

It is VERY important for everyone to understand what that lemon test of John Hesselberth's is all about.  It is a "Rule IN" test.... not a "Rule OUT" test.  What this means is that if the piece changes surface or color under the lemon (or the vinegar test).... then it is FOR SURE leaching materials.  If it does NOT change.... it is NOT saying that it is NOT leaching.  That is very important to understand correctly.  Using t his as a substitute for a LAB TEST is not appropriate.

 

best,

 

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

[Bob Coyle]

Most keys are brass alloys of some sort. That means you may have zinc,tin or lead as well as copper in the glaze. If you come up with something that looks really great, you can buy powdered copper in different gits and be assuered of purity. I use this for electroforming. I tried 100 mesh copper flake in a clear glaze once on a test tile and got some green but it mostly went to copper oxide. I think It would be real interesting to try in a reduction fire.

[TJR]

O.K.;

Maybe not on bowls then. But definately worth persuing.

Do not lick your tests either.

TJR.

[MMB]

So this was a test piece, the test was also the handle addition, but I didnt glaze the interior with the shaving mixture, just plain clear glaze. The shavings were applied within the red line. Im not evading the true situation at hand but inquiring upon a side question...Does the location of the would be could be "tainted" glaze matter if it is not in direct contact with the food. I did the lemon test and there was no leeching.

 

[Guest JBaymore]

Hard to say.

 

If the alloys of the keys (or whatever else occasionally gets "buffed" on that machine) contain lead compounds... and brass alloys often do....... then the lead is almost for sure fuming out of the glaze at cone 6.  Those fumes (fumes are tiny particulates... not gases) are depositing on everything in the kiln..... the other glazed areas of the same piece, the posts, shelves, the pots not even glazed with the key shavings, etc.  And if the kiln vent is not holding a negative pressure on the chamber... are leaking into the room.

 

How MUCH of this is happening........???????  Lacking accurate lab testing of the raw material or the fired products... you and I and others don't know.  Is it huge amounts of lead fumes produced?  Almost for sure not.  Is it enough to be a potential problem?  Maybe... maybe not.

 

When you are working this way it is all a lot of question marks.

 

To me that Oribe-type glaze looks perfectly reproducable using materials form a ceramic supplier.  Those commercial materials are relatively chemically pure...... and I can get a typical analysis of them.  They are intended for use in ceramic process.  Key shavings are not. 

 

So the question for me then becomes .... why use the key shavings which very likely might have some "questionable" content?  I can immediately see four potential answers ... or a blend thereof: 

 

One..... the key shavings are free ...so money can be saved on supplies.

 

Two...... the key shavings are getting recycled so it is doing "good things" for the ecology/planet/etc.

 

Three..... it produces visual results that can not be gotten any other way.

 

Four....... using local non-traditional materials provides enjoyment and challenge.

 

 

The potential negatives that I readily see are:

 

One........ it is possible that the glaze has some toxic components that could be leaching out.

 

Two...... if there are toxic components, they may be potentially harming the users of these products... likely very slowly.

 

Three...... there is legal responsiblity for any harm caused by products produced.

 

Four...... the material is not intended for use in the manufactuire of such products, so defending its use in the case of problems will be difficult.

 

Five...... firing the materials may be slowly contaminating the kiln, shelves, posts, and the studio environment.

 

Six.... there is no accurate information about exactly what this raw material is chemically.

 

 

How these concepts all "balance" each other is what you probably have to weigh for yourself.

 

best,

 

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

[MMB]

As always Jbaymore your responses and participation in any threads on this forum is very much appreciated. I have only fired my kiln up 3 times in the past two years to test those shaving additions and there have been many other firings between them all. I will also say anything I have produced, and ever produced, has been a non-functional item. It is until recently that Ive been wanting to get into the functional world. Ill chalk this idea up as a not worth while one. I guess in all reality there are already many glaze recipes and raw materials out there that are tried and true to use. Maybe if I had a second kiln I would consider toying with this idea more, but after what Ive read its just not worth sacrificing everything else I put in the kiln. Thank you all for your responses.