Trouble With Red

[Guest JBaymore]

Great to see the price went DOWN from the old $25 starting point.  Rare thing these days.

 

best,

 

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

[Min]

One other thing I would do that I didn't see on the lab sites directions would be to wash the test piece that you are sending in with hot water and soap before sending it off. Have no clue if Cadmium would fume, doubt it though, but remember that thread John B posted from Carty about copper glazed pots leaching far less in the testing if they are washed first. Probably won't make a difference for Cd but not 100% sure.

[Pugaboo]

I wanted to give an update on my glaze testing for those of you following this thread.

 

I sent off 2 cups to be tested made according to their instructions. It cost me with shipping both ways $66.

$18 testing fee for each cup =$36

And $30 shipping ($15 each way)

I could have saved the return shipping by not having them sent back but I want to keep them in the studio for my records.

 

I used a combination of Coyote Glazes in:

Buttercup Yellow, Orange, Red Orange and Desert Sage on one cup

And the same glazes with a layer of Amaco Zinc Free Clear over them on the other.

 

Since I was combining several glazes I wanted to test to make sure the glazes were food safe after firing. The clear I did out of curiosity to see if putting clear over another glaze changes anything. It did not, both tested exactly the same which I find interesting. Locally I have talked with other potters and been told that if you put a clear over a non food safe glaze it automatically makes it safe, in this instance both pieces tested the same the clear on top made no difference.

 

I had the pieces tests for Cadmium. The regulations state anything under .5mg/l is acceptable. Mine came back testing at Less Than <0.01mg/l. So they are testing way below the required limits. If was a relief to see that as you all know from my previous posts I was really stressing over this. For record keeping I put cones 5, 6 and 7 on each shelf in the kiln when I fired the test cups. I marked the cones and in my log book where the cups were positioned in the kiln. I have placed the used cones and official lab report inside the test cups as well as writing in sharpie on the outside the date and test results on each cup. I hope I never need them but it's nice to know I had them tested.

 

Things I would do differently next time;

I would send 6 cups with different glazes and skip the clear over the top test since that question has been answered my satisfaction. 6 cups is the most I can fit in the size flat rate priority mail box I used and would cut down on the shipping costs per cup.

Even though all of my glazes state they are lead free I would probably go ahead and test for Cadmium and Lead just so I have it on file.

 

Things I am planning to change OR have already changed due to discovering Encapsulated Cadmium:

All of my drinking vessels, pitchers, most bowls, and large serving bowls will have either a white or a food safe Temmoku interior. That doesn't mean I won't have color on my pieces, I am just redesigning as much as I can to keep the feel of the piece but removing these glazes from food contact areas where I can. This can be difficult at times since I use a lot of Underglazes in my design work. The way some manufacturers seem to go out of their way to make it difficult to find out what they have in their stuff has me researching and downloading MSDS sheets whenever I can find them. I have already starting mixing and using my own colored slips for background colors rather than using commercial Underglazes. I have ordered additional glaze mixing materials and plan to start making and testing my own glazes. As I get these to the point I can get satisfactory results I will send them off to be tested, I can't even begin to say how much peace of mind doing so has given me.

 

I hope this helps answer some of the questions some of you might have in this subject. Getting your own stuff tested is the only way to know for sure.

 

T

[Guest JBaymore]

One other thing I would do that I didn't see on the lab sites directions would be to wash the test piece that you are sending in with hot water and soap before sending it off. Have no clue if Cadmium would fume, doubt it though, but remember that thread John B posted from Carty about copper glazed pots leaching far less in the testing if they are washed first. Probably won't make a difference for Cd but not 100% sure.

 

Can't remember if I have ever mentioned this in THIS thread (not reading back now)... or anywhere here on the CAD forums.........

 

In Japan, the famous "Oribe" green copper glaze is loaded with copper.  One of the standard parts of using that glaze for Japanese potters (that is not all that well known here in the USA) is to take the pieces that are glazed with it and soak them in a solution made from crushed chestnut shells overnight.  Basically it is an acid bath.  It "clears" the hazy look of the glaze as it comes out of the kiln.  It is taking the "loose" copper off the surface and in the immediate surface layer of the fired glaze.

 

I also note that many "American" versions of "Oribe" greens are so loaded with copper that they cause little black microcrystalline surface silicate precipitations to form.  Those areas will be way less stable in holding the copper than fused glassy phase glaze.

 

The acid soak makes a huge difference in the look of the glaze. 

 

best,

 

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

[Guest JBaymore]

.............................. I can't even begin to say how much peace of mind doing so has given me.

 

I hope this helps answer some of the questions some of you might have in this subject. Getting your own stuff tested is the only way to know for sure.

 

T

 

Good for you! 

 

best,

 

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

[Min]

 

One other thing I would do that I didn't see on the lab sites directions would be to wash the test piece that you are sending in with hot water and soap before sending it off. Have no clue if Cadmium would fume, doubt it though, but remember that thread John B posted from Carty about copper glazed pots leaching far less in the testing if they are washed first. Probably won't make a difference for Cd but not 100% sure.

 

Can't remember if I have ever mentioned this in THIS thread (not reading back now)... or anywhere here on the CAD forums.........

 

In Japan, the famous "Oribe" green copper glaze is loaded with copper.  One of the standard parts of using that glaze for Japanese potters (that is not all that well known here in the USA) is to take the pieces that are glazed with it and soak them in a solution made from crushed chestnut shells overnight.  Basically it is an acid bath.  It "clears" the hazy look of the glaze as it comes out of the kiln.  It is taking the "loose" copper off the surface and in the immediate surface layer of the fired glaze.

 

I also note that many "American" versions of "Oribe" greens are so loaded with copper that they cause little black microcrystalline surface silicate precipitations to form.  Those areas will be way less stable in holding the copper than fused glassy phase glaze.

 

The acid soak makes a huge difference in the look of the glaze. 

 

best,

 

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

 

 

Interesting read John, thanks. I wonder if the tannins from the shells are acting as a mordant in some way also?