Saturday, December 22, 2012

Sintering Considerations

by Janet Alexander
Technical Advisor

When firing your clay in the kiln, there are a few things to think about: support, placement, heat, and time.

I like to place my sterling (for the first firing) and fine sliver pieces in a fiber bowl with vermiculite to support them. If I have an item with a wide side, then that side is placed perpendicular into the vermiculite. This avoids sagging because gravity has less effect. 

Be sure to raise the bowl off the kiln floor so that the heat can move around the whole thing. This keeps the bottom of the bowl from being cooler. If you don’t use a bowl, then raise the kiln shelf off the kiln’s floor and support the items, if needed, using fiber blanket or thick fiber paper.

Always note the locations of the kiln’s heating elements. Most front-loading kilns do not have elements in the door, so the front of the kiln will be slightly cooler than the back. Top-loading kilns tend to heat more evenly throughout. If an item contains a stone or sterling silver embedded element, place it towards the cooler area of the kiln. Note that you should never fire pieces with sterling silver embedded objects higher than 1200 degrees F, but do fire them longer to assure they attach.

I have discussed the importance of testing your kiln temperature at different degrees in the past. I cannot stress how important this is. Some members of the local Metal Clay Guild in Dallas recently tested their kilns and found kilns up to 10 degrees F higher than the kiln’s readout.

Sintering time can be a challenge in some circumstances, for example, in a classroom setting where time is at a premium. It is always best to sinter metal clay for the longest period of time recommended by the manufacturer whenever possible. If attaching pre-fired items together, then heat the piece as high as allowable for the metal with the lowest melting temperature and fire for the longest time.

Until next time have fun claying around!

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