Wednesday, November 28, 2012

Is it Sintered or Not?

by Janet Alexander
Technical Advisor

I recently had someone ask me some questions about a fired metal clay piece that broke from trauma from being hit. They didn’t know if it broke because the clay wasn’t sintered or if it broke because of too much stress. They said the exposed cross-section of the break was a chalky white. It broke where the bail attaches at the main body and in some other thin areas on the pendant.

A good way to find out if the piece isn’t sintered is to take a sharp object like a needle and scrape the broken inside area. If it falls apart then it isn’t sintered. If it becomes shinny from the scratching then it’s sintered.The chalky white color is just the metal not reflecting light because it is rough and porous.

Due to its particle makeup, metal clay is not as strong as sheet no matter how long it’s fired in the kiln at 1650 degrees F. On a molecular level it is porous and those tiny holes reduce the fired metal clay’s tensile strength.

With that in mind, design your pieces so that stronger in areas that will receive the most stress. For example, if you have a bail that attaches to the main body of the piece then make it thicker where it attaches instead of a thin connection. If your design requires that it be thin in that area then re-design it so that the bail is hidden behind the piece.

I hope this answers your questions. Please email me or post a comment if you have any questions about your clay.

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