5. Jim Cooper's Translucent
Porcelain AlO-11

Grolleg nO
Custer feldspar 12.5
F-4 feldspar 12.5
Nepheline Syenite 5
Pyrophyilite 5
200 mesh allica _15

100

Add: 2% Veegum T.
0.3% Epsom Salts
(156 grams per 100 Ibs.
dry material).

Nepheline Syenite: A sodium based feld-
spar. All sodium-based feldspars such
as F-4, NC-4, Minspar, and nepheline
syenite melt approximately twice as fast
as potash-based feldspars such as
Primus, Norfloat, Custer, G-200 and K
Spar. Sodium is a more active alkall
than potassium producing a lower vis-
cosity glass which takes other materials
in the body into the melt somewhat
faster than potash feldspars. (I have not
found deflocculation problems usingJim
Cooper's Porcelain, perhaps because |
use acidic water for mixing clay.)

I have found reduced warping and
slumping with Jim Cooper's Porcelain
in comparison with other highly fluxed
porcelains containing 30% feldspar. Yet
even a lightweight attached handle on a
thin-walled cup will pull the cup out-of-
round at Come 10, using this clay body.

This ts the first of two parts of an article
which first appeared in the most recent
issue of The Studio Potters’ Network. It has
been revised by Davidl as a result of
Jurther testing on his part. Part 2 will be
printed in Januany and covers testing
and micing of the aboue recipes. Thanks
to Studio Potters’ Network and to David
Beumdée, He ts a member of the Boulder
Potters' Guild. Address: 806 E. Baseline,
Lafayette, CO 80028,

Table: Properties of Tested Clays

Workability | Transiucency

Absorption

Whitenses at Cone 10

Shrinkage
at Cone 10

Excellent Very Lintle

Stighth Oreyed

1a

OTS 110

Excelbernt

Slight

Excellerit

Excellent

1?

GTS 3-10

Exeelent Almost None

14%)

GTS 2-10

Excellent Very Stight

None

17%

GTS 2-10

Excellent Excellent

Exeellent Slight

Slight

17.

GTS 3-10

December, 1991

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