Wanda Holmes at Alistia on wed 9 jan 02
This tile maker got a wild hair and decided to make a bowl for a Christmas
gift. Against all odds, the bowl turned out beautiful, at least it was
beautiful before I glazed it. I used a glaze that I had thoroughly tested
on tiles and had had no problems with. The bowl was made of the same
claybody and fired the same as the tiles in both the bisque firing and the
glaze firing. On the bowl, the glaze "erupted" in dozens of places leaving
bare clay circles with a thin, almost invisible, arc of covering glaze.
Running my hand over it produced a sound very similar to jumping on bubble
wrap as the bubbles burst. The bubbles ranged in size from very tiny to
3/16" to 1/8" inch in diameter. The bowl was a large shallow shape with a
flat rim 1-1.5" wide. The bubbles were all over the inside walls, the top
of the rim, the outside walls, the edge of the rim, and the underside of the
rim. The only part of the bowl free of them was the inside bottom. Here's
my question, is it likely that the critical difference in behavior of the
glaze is the flat, glaze on the topside nature of a tile vs. the 3D aspect
of the bowl? Could it be that I fire my tiles resting flat on the shelf and
that that influences how they fire vs. being "suspended in midair" as most
of the parts of the bowl were?
I fired to cone 6 in a computer-controlled electric kiln with a vent. I can
supply the firing program if it will help.
I reglazed and refired the bowl. Most of the original bubbles healed, but
new ones formed in the 2nd firing.
Any clues as to what happened would be greatly appreciated. I've reviewed
several sources on blisters, pinholes, and bubbles, but none of the causes
stated seem likely in this case.
Wanda
linda blossom on fri 11 jan 02
Wanda,
I have fired the same glaze on tiles and bowls or sinks and not had the
problem you described. I have had to take in consideration the run factor
since it doesn't matter on tiles so much. Maybe you should repeat this
glaze on another form as there could have been something else going on. Any
number of things and some you could not even imagine. It is fire and clay
after all.
Linda
> This tile maker got a wild hair and decided to make a bowl for a Christmas
> gift. Against all odds, the bowl turned out beautiful, at least it was
> beautiful before I glazed it. I used a glaze that I had thoroughly tested
> on tiles and had had no problems with. The bowl was made of the same
> claybody and fired the same as the tiles in both the bisque firing and the
> glaze firing. On the bowl, the glaze "erupted" in dozens of places
leaving
> bare clay circles with a thin, almost invisible, arc of covering glaze.
> Running my hand over it produced a sound very similar to jumping on bubble
> wrap as the bubbles burst.
Jim Larkin on sat 12 jan 02
Wanda,
Possibly the difference in glaze appearance between your tile and bowl can
be thickness of application if you are dipping the pieces. An object of
lesser mass will absorb a thinner layer of glaze than a more massive object
if held in the glaze bucket the same length of time. That is often the
problem with a lid and a pot, for example. The lid gets a thinner
application of glaze than the pot and as a result doesn't match the pot if
it is a small lid and not double-dipped. Maybe that applies to your
tile/bowl problem.
> > This tile maker got a wild hair and decided to make a bowl for a
Christmas
> > gift. Against all odds, the bowl turned out beautiful, at least it was
> > beautiful before I glazed it. I used a glaze that I had thoroughly
tested
> > on tiles and had had no problems with. The bowl was made of the same
> > claybody and fired the same as the tiles in both the bisque firing and
the
> > glaze firing. On the bowl, the glaze "erupted" in dozens of places
> leaving
> > bare clay circles with a thin, almost invisible, arc of covering glaze.
> > Running my hand over it produced a sound very similar to jumping on
bubble
> > wrap as the bubbles burst.
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tomsawyer on sat 12 jan 02
Wanda,
You wrote " This tile maker got a wild hair and decided to make a bowl for a
Christmas gift. Against all odds, the bowl turned out beautiful, at least
it was beautiful before I glazed it. I used a glaze that I had thoroughly
tested on tiles and had had no problems with. The bowl was made of the same
claybody and fired the same as the tiles in both the bisque firing and the
glaze firing. On the bowl, the glaze "erupted" in dozens of places leaving
bare clay circles with a thin, almost invisible, arc of covering glaze.
Running my hand over it produced a sound very similar to jumping on bubble
wrap as the bubbles burst.
In recent months, I've really been bitten by the glaze testing bug. I had
been using "L" shaped extruded test tiles and have been disappointed several
times when I've had something really good on the tile that looks like c....
[well you know]. So I made a major switch and am now only testing on small
3-4" thrown bowls. Just for the fun of it I did several tests on a tile and
bowl simultaneously. There can be a big difference. After having a tile look
great and mixing a big batch for dipping and having suffered
disappointments, I don't think I'll ever go back to the tiles. In Jim's
answer to you previously, he may have hit upon the correct answer;
unfortunately, I have never had any "formal" training [well maybe not
unfortunately] but I am learning thru experience.
Tom Sawyer
tsawyer@cfl.rr.com
Bobbi Bassett on mon 28 jan 02
We made it a practice several years ago to use tiny, about 2"to 3", vases for
our glaze tests. Not only do we get to see the behavior of the glazes on
vertical surfaces as well, but there is a market for these tiny vases. I
always have a basket of them in the studio for $5 each and customers can't
resist buying several each time they come. I keep the "great" glaze outcomes.
As we all know that means I don't keep too many.
Bobbi in PA
Concepts in Clay
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