Pfeiffer, Dan (Dan R) on mon 10 apr 06
=20
We had a very odd thing happen in the last firing and I am wondering if
any one else has seen a difference in how a glaze matures on ware that
is large and flat. Our ^10 transparent light blue went opaque and crazed
and crawled. The same glaze work fine on a large bowl in the same
firing. My guess is it was quite a bit thicker on the flat piece but in
thinking back on other work we have done small flat tiles and test
pieces never did this. We has seen something like this a number of time
were large flat and what looked to be immature glazes went together.
Anyone else have this happen or is this just a problem of glaze
thickness? or maybe a local cold spot? We are firing in a pretty small
gas updraft and had cone's not far from the ware and if did make it to a
solid ^10. with a 1 hour soak at 1950F on the way down.
=20
Dan & Laurel in Elkmont Al=20
Pfeiffer Fire Arts=20
www.pfeifferfirearts.com
Potters Council Members=20
Ron Roy on tue 11 apr 06
Hi Dan,
My guess would be - because so much of the ware is in contact with the kiln
shelf - which takes longer to heat up - it is just not getting to top
temperature.
You should try keeping that type of ware in the middle to upper part of
your kiln - where it get the full effect of heating - and slow your firing
down - especially during the last 100C. This will have the effect of
evening out the heat and allowing all parts to get to proper temperature.
RR
>We had a very odd thing happen in the last firing and I am wondering if
>any one else has seen a difference in how a glaze matures on ware that
>is large and flat. Our ^10 transparent light blue went opaque and crazed
>and crawled. The same glaze work fine on a large bowl in the same
>firing. My guess is it was quite a bit thicker on the flat piece but in
>thinking back on other work we have done small flat tiles and test
>pieces never did this. We has seen something like this a number of time
>were large flat and what looked to be immature glazes went together.
>Anyone else have this happen or is this just a problem of glaze
>thickness? or maybe a local cold spot? We are firing in a pretty small
>gas updraft and had cone's not far from the ware and if did make it to a
>solid ^10. with a 1 hour soak at 1950F on the way down.
>
>Dan & Laurel in Elkmont Al
>Pfeiffer Fire Arts
>
>www.pfeifferfirearts.com
>Potters Council Members
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Pfeiffer, Dan (Dan R) on wed 12 apr 06
=20
Ron,
This look right to me especial as in the last firing we were trying to
go very fast up on ^10. The problem I was working on is that the copper
washes out it I go slow or spend too much time at the high end so the
plan was to go up fast, >300F / hour, and then jump down to 2000F and
soak for awhile. This made for a very nice dark green but after a very
days in looking closer at some other pots from that load I see other
light blue things are crazing. This has me wondering just how much to
trust in the cones. When we go slow the glazes we use melt very well at
^ 9 and much past ^10 they bubble and have a burnt look. This time we
had ^10 and on one shelf ^11 and I am not sure any of the glazes really
fully melted, they just do not have there normal transparent look.
I guess this week I will try the fast rise to almost ^10 then slow to 10
and drop just a little, maybe 100F, and soak for an hour to try and get
things in the melt and than drop to 1950 and try to get the pinholes to
seal. The clay does have iron in it and it we stay too long at ^10 it
makes a very nice looking iron specks but adds to the hole problems.
Quit a dance to get a good pot!
Dan & Laurel in Elkmont Al=20
Pfeiffer Fire Arts=20
www.pfeifferfirearts.com
Potters Council Members=20
RR>>>>You should try keeping that type of ware in the middle to upper
part of
your kiln - where it get the full effect of heating - and slow your
firing
down - especially during the last 100C. This will have the effect of
evening out the heat and allowing all parts to get to proper
temperature.
>>>>
Ron Roy on wed 12 apr 06
Hi Dan,
Just remember - if you are firing fast - the cones will give a false
reading because the ware - especially flat on the shelf will be lagging
behind - simply because it takes shelves a little longer to heat up -
especially thicker shelves.
If the cones were flat on the shelves they would take longer to melt as well.
RR
>Ron,
>
>This look right to me especial as in the last firing we were trying to
>go very fast up on ^10. The problem I was working on is that the copper
>washes out it I go slow or spend too much time at the high end so the
>plan was to go up fast, >300F / hour, and then jump down to 2000F and
>soak for awhile. This made for a very nice dark green but after a very
>days in looking closer at some other pots from that load I see other
>light blue things are crazing. This has me wondering just how much to
>trust in the cones. When we go slow the glazes we use melt very well at
>^ 9 and much past ^10 they bubble and have a burnt look. This time we
>had ^10 and on one shelf ^11 and I am not sure any of the glazes really
>fully melted, they just do not have there normal transparent look.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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