M340 and M390 Casting Bodies

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Recipes of refined materials that have similar fired maturity and thermal expansions to Plainsman M340, M390. Intended for using in make objects that combine plastic forming and casting.

M390 Casting Version 5

Code #


Materials Amt Units
*KT1-4 Ball Clay 50.000 GM 49.02%
Silica 15.000 GM 14.71%
Redart 35.000 GM 34.31%
Iron Oxide Red 2.000 GM 1.96%

Total:102.00 (R)


The objective of this casting body is to emulate and be compatible with the plastic M390 produced by Plainsman Clays (of course, this recipe is usable by anyone as a stand-alone body for casting). This recipe employs 200 mesh refined mineral powders so it fires to a somewhat more homogeneous surface than M390 (the latter is made using 42 mesh quarried raw clays).

In this testing series we learned that it was not possible to get rich red color using only Redart as a dual-purpose flux and iron-source (using enough to get color ends up making the body fire too dense, turning it brown). Iron oxide is thus needed. But, at only 2%, there is minimal impact on the slurry (iron normally gels a slip).

This body fits our standard glazes well. The fired strength is outstanding. And cast pieces adhere to the standard M390 well. If pieces are thin and glazed only inside, special attention must be given to make sure the glaze is not under thermal compression.

This slurry is a delight to work with compared to many other red-burning ones. It does not gel during casting (if deflocculated appropriately), drains well, dries well. The ball clay has been switched to KT1-4, it delivers better casting properties.

We tried twice to deflocculate a batch using Darvan 811. Although it enabled 1.8SG, the casting rate was very slow and inner drain surfaces were rough.

Our best Darvan #7 recipe was 5000 powder, 2200 water, 27 Darvan to produce 3.85 litres at 1.77SG. It does cast somewhat slowly so pieces must be left in the mold long enough to acquire the desired thickness.



Joe: Slipped up a 5 Kg. batch using the following proportions:
L4005D powder: 5000 grams.
Water: 2200 grams
Darvan #7: 27 grams
Yield is approx. 3.85 litres.
Let sit overnight to saturate, and you will see a specific gravity of 1.77 and Ford Cup flow rate of approx. 1:12
Initially, slip will seem thinner than when allowed to sit overnight.
After sitting approx. 24 hours, there was no water that had settled on top of slip.
A cast bowl in the lab for 20 minutes had light distortion developing on top of clay within 8 minutes and light was totally distorted after 20 minutes cast time at which mold was emptied. The bowl released from the mold within a couple of hours and has a nice smooth surface inside and out.
Cut excess clay from top of cast bowl soon after casting, and clay had the slightest indication of tearing. It did not take much to smooth these areas out. This is the best version of M390 casting I have tried so far in this regard.
Although I have read that high iron castin


L4005D fired color at cone 6

Beautiful warm red, very much like terra cotta. Casted very thin but fired strength is pretty good.

L4005D fired C6DSSC schedule

Inside glaze is Albany GA6-b. Outside is G2934Y black.

L4005D handle, M390 mug, no glaze - Cone 6

The casting handle is not quite as bright red. If an exact match is needed more iron can be added to the recipe. However, keep in mind, that will likely produce more gelling in the slurry. The handle survived repeated whacks with a hammer. It is stuck on well.

L4005D glaze compression testing

These thinly-cast pieces were glazed only on the inside using G1214Z (front), G2934 (left rear) and G2934Y black. Out-of-the-kiln the buff-burning body (M340 casting) was already broken. After a light tap with a hammer the G2934Y-glazed L4005D piece cracked vertically and the crack split open (because of pressure from the inside). The G2934-glazed piece shattered into about 15 pieces with a hammer tap. This means these glazes are clearly under compression, not in any danger of crazing. So ware needs to be much thicker to withstand the compressive forces. Or the glazes need to incorporate a little sodium to increase their thermal expansion.

L4005 Cone 6 casting body

Inside glaze is GA6-B, outside is GA6-C.

L4005 Fired Bars

From from cone 8 to 4 (top to bottom).

L4005D fired to cone 4,6,7


SHAB - Shrinkage/Absorption

4 94.73 89.36 39.28 41.21 4.0 5.3% 5.7% 4.9%
5 94.84 89.11 40.43 41.96 5.0 5.2% 6.0% 3.8%
6 94.9 89.14 40.15 41.17 6.0 5.1% 6.1% 2.5%
7 94.96 88.77 40.13 40.7 7.0 5.0% 6.5% 1.4%
8 94.82 88.66 40.37 40.66 7.8 5.2% 6.5% 0.7%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="M390 Casting Version 5" id="184237" key="fdTWvoa5" date="2020-11-14" codenum="L4005D"> <recipelines> <recipeline material="KT1-4 Ball Clay" amount="50.000" unitabbr="GM"/> <recipeline material="Silica" amount="15.000" unitabbr="GM"/> <recipeline material="Redart" amount="35.000" unitabbr="GM"/> <recipeline material="Iron Oxide Red" amount="2.000" unitabbr="GM"/> </recipelines> </recipe> </recipes>

Born: 2017-09-05, Modified: 2020-11-14 17:36:13

M340 Casting Body Revision 7

Code #


Materials Amt
KT #1-4 ball clay 30.000
Silica 25.000
Nepheline Syenite 25.000
EP Kaolin 15.000
Redart 5.000



The objective here was to develop a casting body compatible with Plainsman M340 at cone 6 (similar firing shrinkage and porosity, color and glaze fit). M340 is robust in production (fewer pieces are lost to breakage, warping, glaze fit issues, cracking, bloating, etc). This body, likewise, is easier to use than a whiteware or porcelain casting body. Because this is made from refined minerals it sacrifices somewhat the more rustic (speckled, variegated) appearance of M340.

This mix employs a large particle sized ball clay and an easy-to-cast kaolin in, achieving fast casting. This body is easy to deflocculate. It is plastic, it has the strength to pull away from the mold as it shrinks.

This revision is more vitreous than others already tested. It has proven exceptionally strong, mugs bouncing on the concrete floor when dropping (repeatedly before breaking). Redart is a low melting red-burning clay, it imparts the bone color and enables improved maturity. RedArt does not flocculate and gel the casting slip the way added iron oxide would.

Typical recipe: 7000 powder, 2800 water, 31 Darvan. That produces 1.8 specific gravity and fills a 2 US gallon bucket half full. For us, it is slightly under deflocculated so we refine it if needed after the experience of the first pour.


L3798C cast mugs

The body of the mug was made using a combination casting - jiggering process. The handles were cast.

L3798C cast/jiggered mugs

G2937Y black, G2934Y White, G2926B clear.

L3798G with 2926B clear at cone 6

Outsides are G2806E copper green and G2926B with black stain.

At cone 7 both L3789G and L4005 were very strong

They just bounced on the concrete floor! Repeatedly before breaking.

L4217G, L3798G2, L3778G fired bars

Fired from cone 8 to 4 (top to bottom). G2 is a remake of the L3798G mix (to double check accuracy).


SHAB - Shrinkage/Absorption

5 95.24 89.43 40.59 41.91 5.0 4.8% 6.1% 3.3%
6 95.28 89.14 42.3 43.41 6.0 4.7% 6.4% 2.6%
7 95.34 88.64 42.04 7.0 4.7% 7.0%
8 95.41 88.85 42.94 43.61 7.8 4.6% 6.9% 1.6%
9 95.5 4.5%
4 89.91 40.95 4.0

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="M340 Casting Body Revision 7" id="184078" key="Z44B4FZq" date="2020-10-29" codenum="L3798G"> <recipelines> <recipeline material="KT #1-4 ball clay" amount="30.000"/> <recipeline material="Silica" amount="25.000"/> <recipeline material="Nepheline Syenite" amount="25.000"/> <recipeline material="EP Kaolin" amount="15.000"/> <recipeline material="Redart" amount="5.000"/> </recipelines> </recipe> </recipes>

Born: 2020-09-02, Modified: 2020-10-29 22:23:04