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all-temperature slip formula

updated fri 28 feb 97


Vince Pitelka on sun 9 feb 97

At 10:39 AM 2/8/97 -0500, you wrote:
>----------------------------Original message----------------------------
>We have been experimenting with terra cotta for some of our bisque
>ware. We have had some good effects, but not as consistently as we
>would like.
>Does anyone have a slip formula, that they could share? To date we
>have been using various amounts of Iron Oxide in our regular
>earthenware formula, but perhaps there is a better way.

Dave -
The following is an all-temperature slip recipe which I have used for ages.
It is technically a cone-ten formula, so at low temps it is by no means a
vitreous slip, but it has always worked great for me in all applications.
If you use it thickly (slip-trailing, feather-combing, marbling) in
high-fire reduction firing with over 5% iron added, reduce the potash
feldspar in the base slip an equivalent (% of the total dry batch weight)
amount to avoid bloating and blistering of the slip.

EPK -------------------- 34
Ball Clay --------------- 20
Potash Feldspar ---- 27
Silica -------------------- 19
Total -------------------- 100
Zircopax ------------------ 8


Tan/Gray (ox/reduc) -- 5% Rutile
Light Green -------------- 1% Chrome Oxide
Light Blue-Green ------- 1% Chrome Oxide, 1/2% Cobalt Carbonate
Dark Blue-Green ------- 4% Chrome Oxide, 3% Cobalt Carbonate
Medium Green ---------- 7% Chrome Oxide
Sky-Blue ------------------ 1/2% Cobalt Carbonate
Medium Blue ------------ 2% Cobalt Carbonate
Dark Blue ----------------- 5% Cobalt Carbonate
Light Brown -------------- 3% R.I.O. (Red Iron Oxide)
Medium Brown --------- 7% R.I.O.
Dark Brown ------------- 12% R.I.O.
Black ---------------------- 8% R.I.O., 5% Manganese Diox., 5%
Cobalt Carb.

If you are using slips for polychrome painting, these percentages
may not give intense enough colors. In that case you can boost the
opacifier in the base batch to 12%, and double or even triple the above
oxide percentages. Keep in mind that such powerfully-tinted slips would
only be appropriate for thin application, as in polychrome slip-painting.
A wider palette of slip colors may of couse be achieved with Mason stains.
If you want really intense colors you can use as much as 30% stain, but very
acceptable colors are normally achieved with additions of from one to
fifteen percent.
- Vince
Vince Pitelka - vpitelka@Dekalb.Net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166