Jim Tabor on thu 6 mar 03
Vince and others-
I like to keep history in mind and not discount the accomplishments of
the past that has brought ceramics to the point it is today. Some
porcelains have been made at the low temp of 2012F. The high temp
porcelain is referred to as hard-paste porcelain. The look and feel
cannot distinguish one from the other; however, soft-paste porcelain is
so difficult to control in production, it was replaced in the early
1800's in favor of bone china and hard-paste porcelain. Just because the
common practice today is to work in porcelain at high temperatures, we
should recognize the fact that it hasn't always been that way.
What is known as Medici porcelain was manufactured between 1575 - 1587
in Florence.
"..regular production of French soft-paste porcelain, with the
translucence and whiteness of the Chinese ware, began at St. Cloud about
1695." From the "The Development of European Soft-Paste (Frit)
Porcelain" by W. David Kingery and David Smith of MIT Dept. of Materials
Science and Engineering. Kingery edited "Ceramics and Civilization
volumes I and II. This topic is in Volume I, Ancient Technology To
Modern Science".
Microstructure was determined mostly by scanning electron miscropy,
together with qualitative energy-dispersive X-ray analysis. using Medici
porcelain and other works produced at St. Cloud, Sevres, and other major
production centers in Europe during the 1700 - 1800's.
Analysis of 16 soft-paste porcelain bodies and glazes is given as well
as the phase equilibrium diagrams for the Medici composition and for a
typical French soft-paste porcelain. Bone china, credited to Spode,
replaced the production of soft-paste porcelain by the early 1800's
because the percentage of wasters was so high. The listed bodys range in
silica from 69.18 - 79.59. Alunina range is 1,75 - 4.35 and all contain
some lead with the highest at 9.72%.
Jim Tabor
happy making ^1 "stoneware" or is it soft-paste stoneware?
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unadulterated bullshit. It is completely
impossible to achieve a porcelain or stoneware body at cone 04 unless your
only criteria is degree of vitrification, and that would be absurd. It is
certainly possible to achieve a fritted white or tan body that approaches
vitrification, but it will be brittle and vulnerable, and in no way can it
be called a porcelain or stoneware body.
- Vince
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