Jolee Chartrand on fri 2 jan 98
I am using a commercial ^5/6 black glaze (oxidation) and lately it has
started "popping" off the pieces. Sometimes its globs that fall off and
other times it looks like splatters over surrounding pieces. The kiln
shelves are a mess around any one of these pieces.
I make sure to wash off (and let re-dry)a piece before glazing, applying
less glaze, thinning the glaze and still get this reaction. None of the
other glazes do this (currently) and this black one did not always.
Will call the manufacturer after the holidays unless the wisdom of this
group makes it unnecessary. :-)
Thanks in advance for any advice
Jolee
Wade Blocker on fri 19 oct 01
Rachael,
From your description that only the dishes on the lowest shelf were
adversely affected, means that the temperature in your kiln is not even.
For the next glaze firing try to put cone packs for cone 5,6,7, on every
other shelf and see how the cones behave during the firing.
For your bottom shelf you should use kiln posts of at least 4" in height.
The glaze you had on those small dishes just boiled off.Mia in ABQ.
Rachael Rice on fri 19 oct 01
I opened my kiln today to find that several small slab bowls that I made
had their glazes dripped in a puddle on to the shelf. I had used this
glaze combination of celedon with an alfred Blue over it on the same
shape bowl ( basically very shallow candy dish bowl approximate eight
inches wide and couple inches tall with no feet, waxed bottom) fired
exactly to the same cone 6 with a 15 minute hold with no problems
before. Orton Cone six was totally bent and cone 7 slightly bent. I am
holding at cone 6 to eliminate pinhole problems I was having before.
While there was a thin veneer of glaze still left on the back, it looked
mostly like a clear glaze over the white clay. I am using B Mix 5
glaze. This didn't happen on my wheel thrown bowls that also had the
same combination. They were on different shelves. The slab pieces were
on the bottom shelf. The only thing different that I did this time is
that I just mixed a new batch of the celedon. Both glazes are mixed thin
and applied thinly. I am using the computerized program for cone 6
fired at a slow speed over 14 hours and cooling for about 18 hours. Any
ideas what went wrong this time. Thanks
Rachael
Ron Roy on tue 23 oct 01
Hi Rachael,
This sounds like it could be the result of what happens sometimes when we
get a bad case of crawling.
At the beginning of the glaze fire - some glazes go through a shrinking
stage - if they are not well physically bonded to the ware the glaze can
crack up and sometimes fall off the ware - and as the firing continues they
melt on the shelf.
This happens more often when glazes are layered and/or thick. The first
glaze is powdery and does not hold to the bisque very well anyway - the
second glaze shrinks and pulls the first one woff and they both can
relase.
If this is your problem there are ways to reformulate a glaze to make it
"tougher" - replacing the kaolin with ball clay for instance.
The one thing that you should not do with glazes that have some propensity
to crawl - don't glaze em and put em in the kiln and start firing them -
let them dry well - this helps get the water out of the ware so it does not
help lift the glaze off the pot as the temperatures in the kiln turn the
water to steam.
Send me the recipes if you like - I can sometimes spot which glaze is the
problem and suggest a fix.
RR
>I opened my kiln today to find that several small slab bowls that I made
>had their glazes dripped in a puddle on to the shelf. I had used this
>glaze combination of celedon with an alfred Blue over it on the same
>shape bowl ( basically very shallow candy dish bowl approximate eight
>inches wide and couple inches tall with no feet, waxed bottom) fired
>exactly to the same cone 6 with a 15 minute hold with no problems
>before. Orton Cone six was totally bent and cone 7 slightly bent. I am
>holding at cone 6 to eliminate pinhole problems I was having before.
>While there was a thin veneer of glaze still left on the back, it looked
>mostly like a clear glaze over the white clay. I am using B Mix 5
>glaze. This didn't happen on my wheel thrown bowls that also had the
>same combination. They were on different shelves. The slab pieces were
>on the bottom shelf. The only thing different that I did this time is
>that I just mixed a new batch of the celedon. Both glazes are mixed thin
>and applied thinly. I am using the computerized program for cone 6
>fired at a slow speed over 14 hours and cooling for about 18 hours. Any
>ideas what went wrong this time. Thanks
>
>Rachael
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
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