Expert: Sam Kelly - 2/26/2009

Question
Hi Sam,

I finally have my own kiln!

Anyway I have done two bisque fires and one glaze fire (1280 degrees C) and then noticed that the bottom kiln shelf (the one that protects the bottom bricks) and the very top one had the bat wash flacking off it it large patches. Did I do something wrong? I followed the directions for making up the bat wash. Do I just use  a stiff brush on them and re apply the wash?

Also can you please explain the  use of the  oraton cones I want to use a cone setting on my harco controller (harco numbers) and I am having trouble selecting what cone to use for my southern ice porcelain they recommend 07 06 05. I am firing to 1000 degrees C.

I don't understand what when fired at 60 degrees c or 150 degrees c.

I program my kiln to fire to 600 @ 60 degrees/ hour then 1000 degrees @ 100 degrees/ hour  I don't see how the 60 or 150 fit into the equation.

I'm firing to cone 9 or harco 90 for my glaze fire

Hope this makes sense.
Thank you

Answer
Kerry, you will have to get the flaking batwash off, it will end up in the glazes on your pots. You probably applied it to thick, you don't need a lot. If you think a pot might have glaze run then sit it on ordinary sand or calcined alumina.

06 for bisque
9 or 10 for glaze

Read this about cones:

http://www.walkerceramics.com.au/cones.htm



"I don't see how the 60 or 150 fit into the equation".
Cones bend (in theory) at slightly different temperatures with relevance to heat applied(temp) per hour

Read this:

http://www.walkerceramics.com.au/cone_temperatures.htm