gshaffer on mon 31 dec 01
Ron.......
To take the discussion on hawthorne bonding clay just a bit further and
why I have reduced the % in my body. I once used 50 % hawthorne but
began to have problems with glaze blisters around handle attachments and
any recessed areas. I took the % of hawthorne down to 30 % and still
occasionally would have a blister or pinholes. It did not seem to matter
a bit about how I bisqued, neither temperature or length of burnout. I
further tested the same body with varying percentages of hawthorne
reducing it 5 % each time. Any body below 20 % was free of pinholes or
blisters all the time. I too like some fireclay in the body for the
reasons you mentioned, iron specks and workability. I always screen my
fireclay even after switching to the supposed 50 mesh hawthorne and I
have gotten pieces of stone and other matter as large as 1/4 inch chunks
in my screens. I know other potters who get away with higher percentages
of hawthorne and sometimes wonder about things that may contribute to my
problems such as % of flux and vitrification and how a more melted body
might gas out more.....i wonder about the gas I fire with, natural gas,
and how the gas in my area may contain more impurities maybe not
allowing the gasses to escape my clay body because the atmosphere may be
already sulfur saturated from the gas in the kiln. I wonder a lot...but
I mostly do what works to keep pots coming out of the kiln marketable.
Thanks for your input and help you are truely a great asset to the clay
community.
Gary Shaffer
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