John Britt on sun 2 jan 00
David Green wrote the best book I have ever read on cones and it is a
must read for those interested in glaze chemistry! "Handbook of Pottery
Glazes" ISBN: 0-8230-2181-5 I believe it is out of print although it
is available through inter-library loan. (precursor to the internet) He
has devoted the first 60 pages to cones. Although the first 38 pages
are the most outstanding. He discusses Seger's paper in 1886 and the
theory that he used. It is a must read!
The discussion of the thinking process itself makes it important. He
began by choosing materials that were in use in the
porcelain industry on a large scale. (i.e. feldspar, whiting, silica
and kaolin.) He tried to use the purest ingredients , Zettlitz Kaolin,
Norwegian quartz, etc.. You can read it for yourself.
The making of cones is not really a concern for me. It is the knowledge
gained in the process that is important. Orton and other cone
manufacturers provide a product of amazing consistency, accuracy and
at a price that is unbeatable. The time you would spend thinking about
making cones far exceeds the price they charge and that is not even
counting,
making the molds, making the cones or the material cost, etc.
The first cone Seger made was cone 4 and he called
it "4" because of the amount of Silica. K20 -0.3, Ca0-0.7 Al203-0.5
and silica 4.0. From cone 5 upwards the ratio of silica to alumina was
fixed at 1:10 , i.e. Al203-0.5 Si20-5.0 for cone 5 or Al203-0.6 Si02
-6.0 for cone 6 etc. (The flux column remains the same 0.3 K20 and 0.7
Ca0)
The illustrative part is the Silica/Alumina ratio. And when you
understand this, Ian Currie's "Stoneware Glazes" is much more
readable.
So using Insight, I formulated several cone recipes directly from
Seger's theory, only using current materials. (Green gives recipes that
Seger
used but since the materials are unavailable they are not very
accurate.)
For example Cone 9
Custer Feldspar-23.06g
EPK - 20.45g
Whiting - 9.66g
Silica (200m)- 46.82g
The Al/Si ratio is 0.9/9.0
Or cone 8:
Custer Feldspar-22.21g
EPK - 16.65g
Whiting - 9.30g
Silica (200m)-38.84g
The Al/Si ratio is 0.8/8.0.
These are fairly accurate although I have not tested them extensively.
If you want more recipes just let me know, although after reading
Green's book I am sure you will be able to formulate them yourself.
The remainder of Green's book is great too. He has great charts and
graphs on Rock materials, ash etc.
--
Thanks,
John Britt claydude@unicomp.net
Dys-Functional Pottery
Dallas, Texas
http://www.dysfunctionalpottery.com/claydude
http://www.silverhawk.com/ex99/britt/welcome.html
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