Friday, March 1, 2013

Firing PMC Sterling in a Foil Container

by Janet Alexander
Technical Advisor

Enamellist Merry-Lee-Rae wanted to know how well the new PMC Sterling fires in the home-made stainless steel foil containers. These containers do not flake, scale or oxidize, in the kiln after being heated. So, I set out to find out some information about the foil, made my own container, and then fired some PMC Sterling.

After researching the American Iron and Steel Institute’s handbook, High-Temperature Characteristics of Stainless Steels, I found out that there are two types of stainless steel foil made especially for heat treating items in kilns. These foils are listed as number 309 and 321. Foil 309 has a higher rating and can be fired up to 2000˚ F (1093°C) without scaling. Foil 321 is good up to 1500˚F (816°C).

I found I can purchase a whole roll 12” x 10 foot of foil on line at Grainger. The 309 is more expensive than the 321.
Another advantage of being able to make your own container is that you can make it longer than many ready-made containers, as much as your kiln allows. This comes in handy when you want to make a spoon or longer items. I will be posting two tutorials on making your own boxes with a tab lid later.

Now onto the test. . . 
I made my box 7 ¼ “x 5” so I can use it in the future for longer items. I fired my piece in the recommended two-stage firings with the first stage in open air on the kiln shelf for 45 minutes at 1000˚F. In the second stage, I placed ½” of coconut carbon under my piece, and over my piece. I fired it for an hour and a half at 1500˚F.

My sterling silver piece came out perfect.

 And the box? It held up fine and no flaking!


Anonymous said...

Thanks for trying this, Janet.

Which foil did you use (309 or 321)?

Janet Alexander said...

I had someone email about their foil box disintegrating after the 6th firing. This can happen if the box is heated above the recommended temperature. I will post the table from the same report I found my information from on this blog. It lists all of the stainless steel foils and their recommended temperatures. I have not tested to see if the foil I used lasts after 6 firings. Its something to check out though.

Janet Harriman said...

Thank you for the info on the stainless steel box. It will be handy for some projects.

Carol said...

This is great information! Thank you Janet for all the research you did to find this product!