Jonathan Kaplan on mon 3 jul 06
Greetings:
Eleanora posted some gleanings from Rhode's and Nelson's books
regarding component clay and clay bodies. Here are some general
comments. I don't want to be specific as my methods, procedures, and
design specifications are being saved for a future project.
Nonetheless.........
I have been designing, testing, and blending clay bodies for myself
as well as many others for many years. While in general most of what
Eleanora posted is very useable information, much of what I have
learned over many years is by trial and error as well as taking
risks. The percentages listed will in many cases work, but when
compounding clay bodies it is not only designing the body itself, but
designing a testing procedure that includes shrinkage tests,
absorption tests, and thermal analysis tests with a dilatometer to
measure the expansion and contraction of the body upon heating and
cooling.
My testing procedure pays particular attention to the ratios between
plastics and non-plastics as well as a distribution of particle sizes
within the component clays. I try and select clays that are
particularly blended for the specific application. For instance, I
would not use FC 340 in a throwing body nor would I use Velvacast in
a throwing body. These clays are processed and blended specifically
for casting bodies. I have always stayed away from any coarse grained
fireclays. I am a strong believer in using Pyrophyllite in all my
clay bodies and look closely at the relationships and ratios of
flint, feldspars, and pyrophyllite. I don't use a Wollastonite as it
is a hydroscopic material. Although the needle like structure of
Wollastonite makes for a very strong clay body, I prefer Pyrophyllite.
I have used many of the non-ceramic based additives marketed as
plasticizers and have found only a few to really be superior on a
long term basis. I don't mention them here as I use many of them in
proprietary formulations and they are all "Googleable." I do stay
away from the polymer plasticizers as they are difficult to reprocess
your scrap if they are in the mix. Every clay body is different and
really depends on your specific requirements. If you are on the West
Coast I might look for materials from that area rather then paying
expensive freight costs from the East Coast. There are many very
clean ball clays now and the days of using Old Mine 4 Kentucky Ball
Clay ceased for me along time in the past.
There are ways to design clay body testing using an Excel spread
sheet that are very simple and helpful. Perhaps the best way to learn
about clays and what they each do and contribute to a clay body is to
get some samples and date sheets of the clays you want to use and
start experimenting with them. Reading the books is also helpful and
they provide many guidelines as to procedures.
Best,
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO
80477
970 879-9139
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
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