Jim West on mon 13 dec 99
Well, first a big thanks to all who responded to my problem with porcelain
handles falling off. You guys are great and I'm convinced that there isn't a
ceramic problem out there that someone doesn't have experience and advice to
share.
I haven't had a chance to try the handles again (yet), but I now know what I
was doing wrong. Actually I was probably doing several things wrong. For
one, the mugs were a little on the dry leather hard side. And probably my
biggest sin was not slow drying and letting the moisture equalize. I just
put the handles on, put them on the shelf, and let them dry. I thought it
would be worthwhile to put all the suggestions together and summarize the
advice.
1. Porcelain has a greater shrinkage than stoneware and any difference in
moisture content between the two parts will cause a different shrinkage as
it dries. This stresses the handle and causes it to fall off. Try to keep
the moisture content of the mug and handle as close together as possible
when attaching handles. The mug should be as damp as possible. Minimize the
moisture absorbed by the handle while pulling it. Allow the handle to
partially dry before attaching it
2. Dry the completed mug slowly to allow the moisture content to equalize.
Wax can be applied to the handle to make it dry slowly. Wrap in plastic,
newspapers, or use a damp box.
3. Shape the handle to fit the mug before attaching. The porcelain has a
strong "memory" that it will tend to revert to as it dries. Invert the mug
after the handles are attached to reduce the stress due to gravity.
4. Make the joints extra strong. Score well. Use paper clay slip to attach.
Press the handle to mug very firmly. Cut an arc in the handle to match the
curve of the mug.
5. Use cider vinegar to attach the handles. This can be either a slip of
vinegar and porcelain used as usual. Or straight vinegar can be brushed on
the mug and handle. This one sounds so easy, I've got to try it. To quote
Ron Roy:
>Here is the drill: Use a brush and smear on some cider vinegar where you
>want to attach the handles. Work it in a bit with your finger. Now put some
>vinegar on the handles where you are going to attach them. I usually put
>some on the outside of the handle as well - especially if you are going to
>bend them. Now a little more vinegar on the mug again and press the handle
>on. No scoring - no slip.
>
>I have not had a handle crack off since I started doing this.
>
>RR
Again, thanks for the advice and I'll let you know how the next batch works
out.
Jim
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