Frank Gaydos on fri 1 jan 99
I use a cone 04 clay body at work/school designed as an all purpose body. As
a result, it does nothing great but does everything adequately. Until this
past semester.
I tried to increase its plasticity to help the wheel workers by increasing
the amount of Bentonite form 1% to 3%. at the same time, I decreased the
fine grog from 5% to 2%.
The problems of cracking on rims and across bottoms started toward the end
of the semester.About four months. Now, it was not a big problem but it was
starting to become more common. We have lots of beginners who just torture
the clay to death sometimes so it has to be forgiving. But I did notice it
on more advanced students work as well. It should be noted I mix equal
amounts of clay slop to new dry mix. I was thinking of changing the
Hawthorne Fire Clay to AP Green fire Clay. I'm thinking APGreen has a larger
particle size?
Will appreciate any feedback. Recipe follows:
CLAY BODY-Cone 04
Redart Clay-25
Ball Clay OM4-12
Fire Clay-6
Goldart Clay-6
Talc-4
Bentonite-3
Fine Grog-5
Barium Carbonate-1
Frank Gaydos
510 Gerritt St.
Philadelphia,Pa.
19147-5821 USA
fgaydos@erols.com
http://www.erols.com/fgaydos
Jonathan Kaplan on sun 3 jan 99
>----------------------------Original message----------------------------
>I use a cone 04 clay body at work/school designed as an all purpose body. As
>a result, it does nothing great but does everything adequately. Until this
>past semester.
>Will appreciate any feedback. Recipe follows:
>
>CLAY BODY-Cone 04
>
>Redart Clay-25
>Ball Clay OM4-12
>Fire Clay-6
>Goldart Clay-6
>Talc-4
>Bentonite-3
>Fine Grog-5
>Barium Carbonate-1
Frank:
Your clay body is way over supplied in plastic materials. On the basis of a
100 pound mix, so to speak, if you use the ratio of plastics to
non-plastics at 70/30 or 80/20, you will notice superior results. Also,
your clay is very deficient in flux and spar and seems to me it is quite
non-vitreous, and has a very high absorbancy. I would also posit that the
shrinkage is very high.
Your formula:
Red Art 25
OM4 12
Fireclay 6
GoldArt 6
Talc 4
total 53
Recalculated to 100
Redart 47.
OM 4 23
Fireclay 11
Goldart 11
Talc 7.5
plastic to non plastic ratio 92.5 to 7.5
This body has way top high fine particle sized materials and could account
for your cracking problems, in fact, I would posit that the high percentage
of plastics does indeed create drying problems and therefore cracking
problems, as you indicate. Even with the grog addition to open the body up,
it still does not eliminate the high percentage of fine particle sized
materials. Your formula also has bentonite it in which further compounds
the problem.
For starters, I would eliminate the fireclay, bentonite,and gold art, and
formulate a body that includes
EPK, Pyrophyllite, perhaps another ball clay, and some flint and Neph Sy,
or even some frit. You could use Cedar Heights bonding also.
By diversifying the materials, you can take advantage of suitable eutectics
at that temperature.
Fo instance
Red Art 30
EPK 15
Tile 6 10
OM 4 10
FHC 5
Pyrophyllite 10
Flint 5
Neph Sy 10
Talc 5
on top:
Barious Carb 1-2% to prevent scumming
Plastics to non plastics ratio 70:30
Of course you could also add some frit and have a really vitreous red body
at cone 4. This formula is only a starting point. There are two kaolins of
differing particle size, two ball clays of differeing particle size, and
red art . Some bonding clay would also provide a coarser partricle sized
material. You can play with the numbers to fine tune, but keep the ratios
at 70:30. In our experience, this provides an optimum balance.
Good Luck
Jonathan
Jonathan Kaplan, president
Ceramic Design Group LTD/Production Services
PO Box 775112
Steamboat Springs CO 80477
plant location
1280 13th Street Unit 13
Steamboat Springs CO 80487
(970) 879-9139 voice and fax
jonathan@csn.net
http://www.sni.net/ceramicdesign/
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