Zero3 Red Stoneware body, white engobe, glaze, firing schedule

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This system of red body, clear glaze, engobe and firing schedule enables the creation of very strong functional ware at cone 03. As strong as high temperture.

Project Name

Zero3 Low Temperature Stoneware System


This began as a project to formulate red and white low fire stoneware bodies that could be used on each other as engobes. However, over time, it because evident that the red body far excelled in strength and the white as an engobe. So that became the focus.

The way to achieve high fired strength at low temperatures has long been known: frit additions. But frit is far more expensive than typical body materials and low-fire did not seem a logical place to make stoneware when it came so natural at cone 6 and 10. But times have changed. Now we think a lot more about energy consumption, so the prospect of firing ten or twelve cones lower is an immediate attention getter. Further, anyone who makes stoneware in electric kilns knows how hard these temperatures are on kiln elements and relays. Imagine making ware of superior strength and density only a cone or two above your usual bisque temperature! That is what we have here.

But the technical challenges are much greater to make this work. That is why we have created the Zero3 Solution. Everything you need is here. And it is open source, no secrets. The problems have been solved. Just do it according to our instructions and you will have brightly colored, high gloss, super strong and safe ware that people will often pick over even porcelain.

And there are no sacrifices in workability. The body is highly plastic so you can make ware very thin. The underglazes paint on like silk and dry enough that in less than an hour you can follow up with incising into the body. The body dries well, sets hard and can tolerate a fast bisque. The glaze glides on like a the best stoneware glaze would (on dipping).

Why was cone 03 chosen? Because 04 is too low and 02 is too high. Almost any low fire underglaze, glaze or overglaze will still work at cone 03. Also it is low enough to still develop good terra cotta red color and bubble free glazes but high enough that minimal frit is needed to densify it.

May 2019: I have been working alot at cone 04, testing dozens of commercial glaze products. I have a Terra Cotta casting body and a new clear glaze that we are really well, see the link below for more info.


L4170 Terra Cotta casting and G3879 UltraClear glaze

Zero3 Stoneware

For use with the Zero3 glaze and engobe

Code #


Materials Amt Units
Redart 15.000 50BG 71.29%
M23 Ball Clay 4.000 50BG 19.01%
Ferro Frit 3110 75.000 LB 7.13%
Bentonite 25.000 LB 2.38%
Barium Carbonate 2.000 LB 0.19%

Total:477,187.20 (R)

Auto Unity Formula + Analysis

BaO 0.01 0.15%
CaO 0.12 0.66%
MgO 0.30 1.22%
K2O 0.34 3.27%
Na2O 0.23 1.44%
(KNaO) 0.57
TiO2 0.13 1.06%
P2O5 0.01 0.16%
B2O3 0.03 0.19%
Al2O3 1.66 17.08%
SiO2 10.52 63.89%
Fe2O3 0.33 5.30%


Si:Al: 6.3:1
SiB:Al: 6.4:1
R2O:RO: 0.6:0.4






The Zero3 recipes (body, engobe, over glaze and firing schedule) are do-it-yourself, they are not in production anywhere (we are working on colored underglaze recipes also).

People who used to use high temperature bodies will be most comfortable with this: Stoneware strength at thirteen cones lower! Saving energy. Putting less wear-and-tear on kiln elements. Doing more brightly colored brushwork (using standard commercial underglazes). A real ultra-clear overglaze that applies perfectly evenly by dipping and dries in seconds. And just as non-toxic.

People who used to do brightly colored terra cotta ware will have more difficulty adapting to this. Most are accustomed to tolerating weak, porous, completely non-functional ware (fired at 06) to get bright colors and warping resistance during firing. That is not what this is about. Zero3 IS NOT TERRACOTTA OR EARTHENWARE. It vitrifies (the clay color is thus darker). Vitreous bodies warp much more easily so extreme shapes are not for this. Ware fired on stilts will warp. This is called "Zero3" because it is fired at cone 03 (firing lower compromises strength, glaze fit, glaze melting and transparency). If you try this body and glaze at 06-04 underglaze colors will appear muted because the over glaze goes cloudy. Firing underglaze colors without a clear overglaze should work well (firing more durable), any commercial underglaze rated for cone 06 should easily survive to 03 (underglazes from different manufacturers can melt very differently).

The work flow in using the Zero3 system is different than for typical clay bodies. The creative effort is concentrated up to the leather hard stage, after that it is a matter of drying, bisque firing, dipping in clear and final firing. Once you adapt a production system could be implemented to ramp up production (unskilled labour could handle everything after leather hard).

Ware strength (and the higher price) comes from the added frit (which is a low melting glass that has been powderized), it melts and glues all particles into a strong matrix (for the white Zero3 porcelain four times the frit is is needed). This mechanism of vitrification permits higher porosity at a given strength.

The Zero3 body (and engobe), mature so low that even at bisque temperatures they have begun to vitrify. Bisque fire ware around cone 010 to be absorbent enough for glazing (if you mistakenly bisque too high heat ware to 200F and then dip it in the clear glaze). The traditional bisque-higher-glaze-lower method is not needed here since the drop-and-hold step on the glaze firing schedule will clear bubbles in the glaze and heal surface defects.

Zero3 Stoneware is highly plastic and very, very slick and smooth. It does not generate large amounts of slip on throwing (as do many terra cottas). Drying is fairly slow (because of the high bentonite needed for the plasticity). Dry hardness is excellent. It works well with Zero3 white slip (when applied correctly), with commercial underglazes (at leather hard stage) and it fits Zero3 clear glaze.

Fired ware passes a 300F to ice-water to boiling water stress test without crazing or shivering (in our lab). Glazed ware has good resistance to thermal shock (when fired at cone 03).

The barium is optional, it is there to precipitate solubles. Try the recipe without it to see if you can tolerate the salts on the fired surface.

Slip Casting

Drop out the bentonite. For 1000g of dry use about 420g water and 7.5 Darvan (for about 1.75 specific gravity). Adjust these proportions to get the best deflocculation.

To Make Traditional Terra Cotta

If you do not want stoneware, just the traditional porous (and weak) terra cotta, then substitute the frit for talc (talc prevents crazing with commercial glazes).


L3724N decorated leather hard mugs

Crysanthos underglaze colors have been applied in multiple layers. These are not engobed on the inside.

12 minute pour gives 3.7mm wall thickness

This 14cm bowl was extracted from the mold in about 30 minutes. The thicker wall has the strength to pull itself away without cracking problems. This was the standard recipe without the bentonite. If kaolin were substituted for the ball clay it would cast faster.

Zero3 N1 mugs

Zero mugs ready for bisque

Zero3 casting bowls (cone 06, 02)

Zero3 body with G2931F Zero3 glaze

The F version of the glaze employs Ulexite to source the boron (instead of frits). These Zero3 stoneware mugs were fired to cone 03 with underglazes. The right mug has the Zero3 engobe inside (under the glaze).

Zero3 stoneware N2 glaze

This is a year old. No crazing yet.


SHAB - Shrinkage/Absorption

1 93.02 90.88 36.09 39.45 -6.0 7.0% 2.3% 9.3%
2 92.86 88.58 38.29 40.09 -4.5 7.1% 4.6% 4.7%
3 94.13 88.32 47.55 49.39 -3.0 5.9% 6.2% 3.9%
4 93.87 87.73 37.55 38.35 -2.0 6.1% 6.5% 2.1%
5 93.66 87.11 38.04 38.06 1.0 6.3% 7.0% 0.1%

LDW - LOI/Density/Water Content

1 25.59 19.86 18.56 22.4% 6.5%

XML (to paste into Insight)

<recipes>XML not functional: We are working on this problem.</recipes>

Born: 2015-01-28, Modified: 2018-12-06 10:01:11

Zero3 Engobe

For use with the Zero3 body and glaze

Code #




Materials Amt
Nepheline Syenite 10.000 9.80%
Pioneer Kaolin 42.000 41.18%
Ferro Frit 3110 25.000 24.51%
Silica 20.000 19.61%
National Standard Bentonite 5.000 4.90%



The Zero3 Engobe finds its inspiration in the ceramic tile industry. Thousands of tons of white engobe are applied to tiles made from red or brown burning bodies, after pressing, to prepare them for glazing. The white surface enables the use of glazes of any color.

This engobe is not required in the Zero3 system, but like tile, it is employed for practical reasons. A typical use case for functional ware is application to inside food surfaces at leather hard state (and covering with the clear transparent Zero3 glaze after bisque firing). Or, as in tile, application to the red-burning body, by dipping or painting, to create a white base onto which coloured underglaze decoration is done. If you are using this engobe on another clay body, especially if not firing to cone 03, do an EBCT test to be sure they are compatible (have the same firing shrinkage), adjust the frit percentage as needed.

This is an engobe, it must be applied at stiff leather-hard stage (if you apply it to dry or bisque it will flake off). It will rewet pieces and they will require significant time to re-stiffen to the same state. Even coverage can normally only be achieved by preparing a slurry of the correct rheological properties and dipping or pouring. It is vital that you have a good mixer and can effectively measure specific gravity. To mix this use the process described on the “Engobe” glossary page at the Digitalfire Reference Library. A paint-on version of this can be made by adding 500g powder engobe to a mix of 400g water and 75g of Laguna Gum Solution (makes 1 pint). This produces brush-stroke coverage, which can be very attractive.

A drop or two of Dettol might be needed to store this for long periods (to prevent bacteria or mold).

Recipe info: The silica helps match body thermal expansion and glaze fit. The frit makes the fired hardness of the engobe more closely match the body. Nepheline Syenite is included as a filler. The bentonite is needed for good adhesion to the leather hard body and for dry hardness.


Engobe applied to leather-hard mug

This was done by simply filling and rotate-pouring the engobe, then pressing the lip into it. Since the engobe gels the mug could be turned over immediately without creating any drips. Notice that the outer surface of the handle has been waxed to slow down its drying. This is because the engobe rewets the mug body, thereby setting it behind the handle. This mug has thin wall so this this rewet adds a day to the production process. This next day the brushwork is done on the outside.

Zero3 body with G2931F Zero3 glaze

The F version of the glaze employs Ulexite to source the boron (instead of frits). These Zero3 stoneware mugs were fired to cone 03 with underglazes. The right mug has the Zero3 engobe inside (under the glaze).

Pulling badly on L212 on EBCT at cone 04


6100 - Red

1400 powder, 1067 water, 5.6 Darvan produced 1.52 SG. Too runny, took alot of epsom salts. Perhaps water could be reduced. Pulling badly at L212 on EBCT test.


EBCT - Engobe Body Compatibility Test

1 engobe L212 1.6mm 15mm/engobe 06
2 engobe L212 1.5mm 10mm 04
3 engobe-brown L212 3.3 03

XML (to paste into Insight)

<recipes>XML not functional: We are working on this problem.</recipes>

Born: 2014-11-04, Modified: 2018-07-02 23:03:40

Zero3 K Cone 03 Transparent Glaze

Code #


Materials Amt Units
Ferro Frit 3195 25.000 KG 26.32%
Ferro Frit 3134 33.000 KG 34.74%
EPK 20.000 KG 21.05%
Ferro Frit 3249 10.000 KG 10.53%
Ferro Frit 3110 7.000 KG 7.37%

Total:95,000.00 (R)

Auto Unity Formula

CaO 0.59
MgO 0.10
Na2O 0.31
(KNaO) 0.31
B2O3 0.76
Al2O3 0.41
SiO2 2.45


Si:Al: 6.1:1
SiB:Al: 7.9:1
R2O:RO: 0.3:0.7






0.20 per kg


This recipe improves the popular Worthington Gerstley-Borate-based low fire clear recipe. It targets cone 03 to work best on Zero3 stoneware and porcelain. However many low fire bodies are dramatically stronger when fired to cone 03 with this (or one of its thermal expansion variants L & H). And the vast majority of commercial glaze products will fire easily to this temperature. If you absolutely must fire lower, to cone 06 or 04, then use the G1216Q recipe instead.

Unlike Worthington something this does not become a bucket of jelly, does not crack on drying, does not go on unevenly or the wrong thickness, does not cloud up with boron blue or micro-bubbles when fired (because it has lower CaO) when used on the types of bodies discussed below. The major development work culminated in the Ulexite-fluxed G2931F. This recipe, G2931K, was formulated to have the same chemistry as F but use frits instead. It is crystal clear and super glassy.

Low fire bodies span a wide range of thermal expansions. While Worthington clear (an ancestor of this recipe) melts to a good clear, its thermal expansion was too far toward the low end of the range (it tended to shiver and fracture rather than craze). This recipe, G2931K, raises thermal expansion (by adding Na2O). The thermal expansion of Zero3 stoneware and porcelain are about the middle of the range, and they develop good glaze:glaze interfaces, so this recipe fits them well.

This glaze also works well on other low fire bodies. Low talc bodies (like Plainsman 215) also work well. But this glaze shivers on high-talc bodies and crazes on zero-talc porous ones. That is what we want. Why? As noted, the thermal expansions of low fire bodies span a wide range. And glazes are just not stuck on well to ones that have a porous and softer surface. Thus, GLAZE FIT IS VITAL AT LOW FIRE (to prevent crazing and shivering). Remember this: IT IS IMPOSSIBLE THAT ONE BASE GLAZE CAN FIT THEM ALL. Not even two can span the range! Commercial glazes only fit your clay body by accident. That is why this recipe has three variations, one of higher expansion than this one (G2931H) and one of lower expansion (G2931L). By testing glaze fit (using a thermal shock test like boiling water:ice water) and choosing the best recipe or blend of recipes, you can get the best fit. Make the effort and do that. All three fire crystal clear. And you can make make your own brushing versions (see link below). Keep in mind that adding zircon and stains changes expansion and requires re-testing and possibly changing the proportion of K, H and L to match your body. It is a hassle, but it is not rocket science.

Dipping ware in Zero3 Transparent is just so much easier than trying to paint on commercial, slow-drying clears. It produces a slurry with very nice suspension, fast drying and good application properties (if you tune it right). It naturally gels to a creamy consistency at around 1.53 specific gravity (in our circumstances). However it goes on too thick at that high a value, we have found the best all around performance at 1.43 with enough Epsom Salts to gel it back up to a creamy consistency (a few grams per gallon). Measure the SG by weighing (forget about fiddling with hydrometers). You will think it is too thin and watery, but it isn039;t. The Epsom salts will thicken it and make it thixotropic (which the 1.53 slurry was not). Use a little Darvan if you get it too thick.

As a clear overglaze to finish your decorated ware, this glaze has a number of other advantages over commercial clear glazes:
-It is much less expensive so it is practical to have a large pail of it so that pieces can be easily dip-glazed (using dipping tongs).
-It behaves like stoneware glazes, it suspends well and applies in an even layer that can dry to handling stage is seconds.
-It fires to a better crystal clear than most.
-Since the recipe is known, and contains no toxic materials, you can more confidently assure retailers that it is safe; all underglaze color decoration can be isolated from any contact with food or drink by this.
-It is compatible with most underglaze colors (including pinks).

Pay special attention to the drop-and-hold firing schedule, especially if your clay body is not fine-grained.

To mix up 5 Kg use about 4.5 kg of water to get 6.5 litres of glaze.

To mix up paint-on consistency (1 pint jar):
-113g Laguna Gum Solution (100 grams of gum solution has 6.5g powdered CMC Gum)
-200g water
-Mix in 500g of powdered glaze, adding water if needed to get desired painting consistency (up to 325g total water). It is better to be a little thinner than too thick.
-To make colored versions add stains as needed (if stains cause micro-bubbling or orange peel surface include 2-3% zircopax).

Batch Ticket Notes

These notes were entered in the notes panel under "Batch Ticket Notes"


Glaze fit test

How to tune the thixotropy of a glaze

How to convert a d..o a brushing glaze


G2931K on Zero3 Stoneware

Fired cone 03. Body is Zero3 stoneware. Surface is perfect, even where thick. Ultra clear. Survived three boil:ice cycles and one 300F:ice cycle without crazing.

G2931F vs. G2931K on Polar Ice Low Fire

2931F was the Ulexite flused version of this recipe. The F survived three boil:ice cycles and 1 300F:ice cycle without crazing or shivering. The K is slightly smoother, tiny dimples in the surface are fewer. It is also applied thicker.

G2931F vs G2931K fritted - terra cotta mugs cone 03

F was the Ulexite-fluxed version of this recipe.

G2931F vs G2931K flow test

These two recipes have the same chemistry, but K sources boron from frits rather than Ulexite. Notice how much less bubbles there are in the flow and how much more predictable the melting pattern is.

G2931F vs G2931K - Melted balls at cone 03

F, the Ulexite version, is obviously bubbling more, the percolation is causing the melt to spread out more on the tile. On the flow test is was less fluid.

Firing temperature is important for Zero3 glaze

This is G2931F on Plainsman Buffstone, L213, F100, L215. First column is cone 04, center is cone 03, right is cone 02. All exited the kiln without crazing except Buffstone at cone 04. We subjected all of them to a 300F:IceWater thermal shock. Buffstone crazed on all of them. L215 and L212 Cone 04 crazed. L213 was good but later the glaze was found to be under excessive compression, subject to shivering over underglazes. At cone 02 there are some dimples and defects.

Three low fire bodies that need three clear glazes

Because of glaze fit. The left-most mug is Plainsman Buffstone, it contains no talc and fires buff colored. The centre one is L212 (about 25% talc). The right one is L213 (about 45% talc, it fires very white). Talc raises thermal expansion. The centre glaze is G2931K, it is middle-of-the-road thermal expansion (Insight-live reports it as 7.4) and fits the L215 (also Zero3 porcelain and stoneware). But it crazes on Buffstone and shivers on L213 and L212. So I adjusted it to reduce its expansion (to work on zero-talc porous bodies) and raise it (to work on high talc bodies like L213). How? By decreasing and increasing the KNaO (in relation to other fluxes). These three can be blended to fit any low fire body.

G2931K glaze precipitates things on storage

G2931K On L212 after a year

Some crazing starting.

K on L215 at cone 04

The thicker version is clouding. The thinner one has micro-pinholes. It needs a higher temperature.

G2931K o L215 - Cone 03, thick application

G2931K on L215 - Cone 03 fired in 30 minutes

Very transparent. No crazingafter many months.

G2931K on L215 - Cone 06

Milky (because cone 06 is underfired for this glaze). But only a little crazing after a year.

G2931K running on Zero3 Casting

This happened at cone 03 and 04. The G3879 (left) did not run. For some reason G2931K easy applies to thickly on this body.

This 1000 gram batch of glaze powde

This 1000 gram batch of glaze powder screened 80 mesh immediately after making, and allowed to sit for 3 months prior to usage. The material in photo was screened out once again after the 3 month time lapse, (80 mesh once again). The largest balls are approx. 2.5 mm. in diameter, and when these particles were screened out, and still perhaps slightly wet?, they were quite easy to break in half with your fingernail.


ST-Untitled typecode

Alternate Code Number:GS04-1

XML (to paste into Insight)

<recipes>XML not functional: We are working on this problem.</recipes>

Born: 2006-03-16, Modified: 2020-06-25 15:42:06

Firing Schedule Name

Cone 03 hold-rise-drop-hold

Degrees (Fahrenheit or Celcius)


Schedule Type


Start Time and Temperature

8:01 am at 80F


Step Degrees/Hr Temperature
Time Note
1 400 240 60 1:24 9:25 am
2 350 1850 30 6:30 2:31 pm
3 108 1950 10 7:35 3:36 pm
4 500 1850 30 8:17 4:18 pm


Used to glaze fire Zero3 porcelain and stoneware. However, there is a caution about bisquing these frit-containing bodies: They will vitrify in a typical firing, you must reduce the temperature to around 1500F (if ware is not absorbent enough fire lower). Note: this schedule is for the glaze firing, the previous two sentences simply referenced what is needed for the bisque.

This can start and finish more than once in a working day. Step 2 can often be done as fast as your kiln will go (cold-to-cold in three hours is possible).

The soak at 240F does not fracture ware even though it is above the boiling point of water. We find this is needed to be sure ware is sufficiently dry to withstand the rapid ascent to 1850. If your ware is thicker a slower ascent may be needed.

The 1850 soak on the way up clears the clouds of microbubbles. The 1850 soak on the way down heals the defects (blisters, pinholes) because the increasing viscosity is enough to overcome the surface tension holding bubbles from breaking).

It may be necessary to alter the last step if any imperfections are present. Try dropping to 1800 or 1750 and holding there. An additional step could be added to cool at 100F/hr down to 1500.