spikes...is kiln too hot, not hot enough or am I holding too

[deborahbur]

I have points on the edges of some of my pieces, square plates and fishes. What should I do to eliminate the spikey glass. They are like little needles?

Thanks
Deborah[/b]

[Heidi]

Deborah,

Needles like you've described are a result of overfiring. Without knowing your firing schedule it's hard to say if it's your temp or timing. With some experimentation you should be able to get the fuse you want without the needles, either by lowering your fuse temp or shortening your time at fuse temp (or both).

If you will post more details like type of glass, number of layers, firing schedule used, it will be easier to offer suggestions to try and help.

Hope this helps,
Heidi

[Steve Immerman]

It also helps to use a kilnwashed shelf, rather than paper.

Also, make sure your piece is two 1/8" layers.

Steve

[Cynthia]

I have points on the edges of some of my pieces, square plates and fishes. What should I do to eliminate the spikey glass. They are like little needles?

Thanks
Deborah[/b]

Lower and Slower
Lower temp, slower ramp up to full fuse. Dependent upon the glass you're using will determine your temps, but assuming it's a 90 or 96 coe glass, you should be able to ramp at about 500 dph (after you exceed the upper strain point) and get to a full fuse at a lower temp than if you ramp AFAP to full fuse and hold. This should help with needles.

Needles are usually because the glass hung up while rounding up or contracting at full fuse, so fiberpapers promote needles since the glass can hang up on the paper, and if you have single 1/8th thickness of glass (volume control issues), it will contract to thicken and you'll see needles in that case as well.

Some things to consider anyway.

[deborahbur]

I am ramping at 400 per hour and after 1100 I ramp as fast as I can to 1490 and hold for 15 minutes. I use kiln washed shelves but I fired 4 layers in a 1027 Skutt kiln.

I have moved my lowest shelf to about 8 inches off the bottom because I was haveing problems with a full fuse on the lower shelf.

Any help with my problem would be greatly appreciated.

Deborah

[Tony Smith]

Deborah,

Is this a ceramic kiln with multiple shelves? Are you having problems on the top shelf? You may be overfiring your top shelf due to uneven temperature distribution within the kiln.

Tony