Wednesday, June 3, 2015

Sintering Considerations

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 silver 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.  Place the bowl raised off of the kiln floor so that the heat can move around the whole bowl. 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 notate 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. If an item has a stone or sterling silver embeddable, place them towards the cooler area of the kiln. If there are sterling silver embedded objects, don’t heat higher than 1200 degrees, but heat 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 higher than the kiln’s readout.

Sintering time is a constant variable depending on the circumstances, for example if there are time constraints due to a classroom situation, or no time constraints. It is always best to sinter the metal clay for the longer period of time allowing the molecules to soften and attach to each other. If attaching pre-fired items together then heat the piece as high as allowable for the metal, and for the longest time.

I hope this helps those of you who have had problems with rings not fitting the finger properly.

Until next time have fun claying around.

Janet Alexander
Technical Adviser

1 comment:

Lora Hart said...

Good tips Janet. I also use vermiculite to support dimensional pieces vertically. An alternative would be to make a type of box or walls with fiber blanket. I also put kiln paper on the shelf if I'm firing a ring. That reduces drag and keeps the ring from deforming.