Ron Roy on sun 5 jun 05
bisque firing in gas kiln.?
Hi Kathy,
So I am suggesting that the cracks happened during the cooling of the
bisque firing - not from the flames but from the cooling draft from the
burner ports.
I have such a kiln and can see how this could happen - protecting the
outside pots with bricks may well do the trick - as would closing off the
burnerports during cooling - not so easy to do however.
It may be much easier to place some sort of covering around the outside of
the kiln at the floor level - to cut down draft and any wind effect - that
would force any draft to come down the space between the metal skin and the
kiln itself and the air would be heated a little - which would help.
If you have the fiber type then the problem is much worse because of the
faster cooling.
If the door is not tight - especially at the top you can also try to block
draft there but with refractory.
I know that kind of dunting crack is hard to see - You can tell which
bisqued pots are cracked because they will not ring when tapped.
RR
>The cracking on the edges is not sharp . The cracks look as thought they
>happened during the cooling process at one stage or another.
> The ambient temperature of the glaze load
>was under 100 degrees when I opened the damper during the bisque and the
>pots
>were cool enough to touch when I opened the glaze load.
>
>I have wondered whether or not one of the factors might be that the kiln
>(Geil 20 cu ft downdraft)
>is designed without bagwalls and that the direct flame hit some of the pots
>during the bisque
>firing and subsequently caused uneven heating at that stage.
>
>I used to bisque all the time in an old catenery arch downdraft with burners
>in 4 corners and
> bagwalls and never had the same issues with cracking so I suspect it had to
>do with
>the ware coming into direct contact with the flames from the burners because
>they go directly up the
>side walls of the kiln.
>
>
>On further inspection of the firing it does seem that those pots fired in
>the bisque
>that were on the outside edges of shelves suffered the most cracks and
>dunts.
>
>I may try the bisque again. but I will cut some softbricks and stack them to
>protect the ware
>from direct contact with the flames.
>
>Any other feedback or suggestions from those using a similair kiln are
>welcomed.
>I want to make the best use I can of this gas kiln until I can afford to
>replace my electric kilns.
>
>Thanks,
>
>Kathy
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
