Randy Peckham on mon 17 dec 01
My bloats look like squash innerds. Does this help to determine if it is a
bisque issue, or a contamination issue? I suppose it could be a
contamination by organic matter, which didn't burn off in the bisque. I
noticed some bark in the bucket, probably from my son. I bisque to cone
06. I have been doing it slower, about 11 hours, but lately I have speeded
it up a bit to about 8 hours. Maybe that coupled with the extra additives
has caused the problems.
I had thought that if I bisqued quickly, then glaze fired slowly the
inorganics that didn't burn off in the bisque would burn off in the glaze
firing. The original reason that I slowed down the bisque was glaze
blistering, but I have found that slowing down the glaze firing fixes that,
so I started speeding up the bisque.
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Ron Roy on sun 23 dec 01
Hi Randy,
I think the squash like innards are a symptom of the kind of cavity the
gases exploit. I have seen these in many different situations.
If the air is not completely out of clay when wedged - think of the clay
almost joined together where there had been an air pocket - the clay is
touching in some areas but there is still the remains of the air which has
not been completely wedged out. As the clay becomes pyro plastic what air
is left - and is expanding - begins to enlarge the pocket - but some of the
clay has become partially joined across it. This results in that fibrous
looking texture. It is the only explanation I can think of.
You can spot those kind of air pockets by slicing up a ball of wedged clay
and bending each slice back in your hands - stretching the surface. If some
air is present those cavities will open up.
Much of the clay we use has that kind of air in it and it would not be a
problem unless the body is over fired - either from the improper
formulation for the recommended cone and/or improper bisquing of clay with
iron oxide in it - which then over fluxes the clay.
I think the next step for you should be to check the absorption of your
clay to see how close it is to being over fired - make sure to give the
test pieces a very clean bisque fire.
I am fairly sure it is not a contamination issue - I have seen that type of
bloating many times and it has been due to air in overfired clay - it's the
way it looks that tends to make you think it's contamination.
Tricky stuff this ceramics - RR
>My bloats look like squash innerds. Does this help to determine if it is a
>bisque issue, or a contamination issue? I suppose it could be a
>contamination by organic matter, which didn't burn off in the bisque. I
>noticed some bark in the bucket, probably from my son. I bisque to cone
>06. I have been doing it slower, about 11 hours, but lately I have speeded
>it up a bit to about 8 hours. Maybe that coupled with the extra additives
>has caused the problems.
>
>I had thought that if I bisqued quickly, then glaze fired slowly the
>inorganics that didn't burn off in the bisque would burn off in the glaze
>firing. The original reason that I slowed down the bisque was glaze
>blistering, but I have found that slowing down the glaze firing fixes that,
>so I started speeding up the bisque.
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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