Michael Wendt on sat 1 dec 01
Holiday wishes to all.
Over the past week, several people have called me on the phone to pose
questions about the causes of cracking and possible solutions and since the
group has often given these answers when asked, I thought I would offer the
questions as part of the Merry Christmas/ Happy Hanukah/ quiz.
1. A pot is wired and left on the bat to dry. When dry, the pot has a
series of parallel cracks on the bottom that seem to follow the path of the
wire. Cause? Cure?
2. A pot is allowed to dry quickly to leather hard, inverted and trimmed.
After it finishes drying, cracks appear starting in the trimmed area radial
to the center axis. Cause? Cure?
3. A pot is thrown with sharp turns in the wall. After it dries, cracks
appear in the sharp turns all around the perimeter of the pot. Cause? Cure?
4. An 18" platter is bisque fired and when unloaded, has a crack that
radiates from the center outward to the edge farthest from the wall of the
kiln and is somewhat gapped. Cause? Cure?
5. Another 18" platter is bisque fired and has an almost invisible hair line
crack that starts at the edge nearest the kiln wall and projects inward to
the center of the platter. Cause? Cure?
6. A lamp base is fired to cone 10 and when cool shows a circular crack on
the wall with cracks that radiate outward from it in random directions.
Cause? Cure?
I will give my answers next time and no doubt there are others who also have
good ideas as to the causes of these problems taken from actual events.
Why a crack quiz? What ruins more work than cracking? The only cracking I
have never had to deal with is "S" cracking. My clay body is only 38% clay,
the rest is feldspar, Neph Sy and silica so it doesn't shrink much (about
3.4%) in drying, and total fired shrinkage from wet to cone 10 is 11%.
Regards
Michael Wendt wendtpot@lewiston.com
Wendt Pottery
2729 Clearwater Avenue
Lewiston, Idaho 83501
1-208-746-3724
wendtpottery.com
Ron Roy on sun 2 dec 01
The Hamer book has 10 pages on cracking - if you can't find any of these
there with the cures it will not be becuase the problem is not covered.
RR
>Holiday wishes to all.
>Over the past week, several people have called me on the phone to pose
>questions about the causes of cracking and possible solutions and since the
>group has often given these answers when asked, I thought I would offer the
>questions as part of the Merry Christmas/ Happy Hanukah/ quiz.
>1. A pot is wired and left on the bat to dry. When dry, the pot has a
>series of parallel cracks on the bottom that seem to follow the path of the
>wire. Cause? Cure?
>2. A pot is allowed to dry quickly to leather hard, inverted and trimmed.
>After it finishes drying, cracks appear starting in the trimmed area radial
>to the center axis. Cause? Cure?
>3. A pot is thrown with sharp turns in the wall. After it dries, cracks
>appear in the sharp turns all around the perimeter of the pot. Cause? Cure?
>4. An 18" platter is bisque fired and when unloaded, has a crack that
>radiates from the center outward to the edge farthest from the wall of the
>kiln and is somewhat gapped. Cause? Cure?
>5. Another 18" platter is bisque fired and has an almost invisible hair line
>crack that starts at the edge nearest the kiln wall and projects inward to
>the center of the platter. Cause? Cure?
>6. A lamp base is fired to cone 10 and when cool shows a circular crack on
>the wall with cracks that radiate outward from it in random directions.
>Cause? Cure?
>I will give my answers next time and no doubt there are others who also have
>good ideas as to the causes of these problems taken from actual events.
>Why a crack quiz? What ruins more work than cracking? The only cracking I
>have never had to deal with is "S" cracking. My clay body is only 38% clay,
>the rest is feldspar, Neph Sy and silica so it doesn't shrink much (about
>3.4%) in drying, and total fired shrinkage from wet to cone 10 is 11%.
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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