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

Share from (Lab Documentation and Calculation System) by Digitalfire.

See Also:
Cone 04 Terra Cotta Casting/Throwing Body, Transparent Glaze, Firing Schedule

Vitreous red body or porcelain, clear glaze, engobe and firing schedule enables the creation of very strong functional ware at cone 03. As strong as high temperature.

Project Name

Zero3 Low Temperature Stoneware System

Project Codenumber



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.

March 2021: We are working on a much whiter version of the engobe, L3685Z2. And two other glaze recipes, G1916Q and G3879. More information coming.


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 (plastic 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). Casting is a possibility, you would have to remove the bentonite and switch to a better-suited ball clay (e.g. KT1-4). Or, increase the RedArt:BallClay ratio. Because of frit solubility, slip rheology would change over time (and require adjustment).

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 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 bentonite content). Dry hardness is excellent. You can get more plasticity if needed by increasing the bentonite (I tried doubling it, the drying shrinkage increased by about 1%).

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 (adjust the ball clay as noted above). For 1000g of dry use about 420g water and 7.5 Darvan (for about 1.75 specific gravity). If the slip is gelling or too thick it is likely under-deflocculated, take a small amount out from the batch and experiment with adding more Darvan. It is more important to listen to your slip than a book.

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.

L3724N2 Zero3 stoneware with G2931K glaze

Fired cone 03. With various Amaco Velvet underglazes tested.


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)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Zero3 Stoneware" keywords="For use with the Zero3 glaze and engobe" id="93157" key="t4YbkvqD" date="2021-09-09" codenum="L3724N2"> <recipelines> <recipeline material="Redart" amount="15.000" tolerance="" unitabbr="50BG"/> <recipeline material="M23 Ball Clay" amount="4.000" tolerance="" unitabbr="50BG"/> <recipeline material="Ferro Frit 3110" amount="75.000" tolerance="" unitabbr="LB"/> <recipeline material="Bentonite" amount="25.000" unitabbr="LB"/> <recipeline material="Barium Carbonate" amount="2.000" unitabbr="LB"/> </recipelines> </recipe> </recipes>

Born: 2015-01-28, Modified: 2021-09-09 15:34:17

Zero3 Porcelain - Experimental

Code #




Materials Amt Units
New Zealand Kaolin 227.000 KG 48.54%
Ferro Frit 3110 300.000 LB 29.10%
Silica 200.000 LB 19.40%
VeeGum T 30.000 LB 2.91%
*Mason 6336 Blue Stain 250.000 GM 0.05%

Total:467,658.00 (R)


*This body is not available for sale. I have done a long series of test mixes in search of a blend of North American materials that will produce a fritted white low-fire oxidation porcelain. But I was not able to do so. The difficulty is that the glassy phase of the frit amplifies the color of any iron available in the body (even tiny amounts) to produce a bone or ivory white.

The only solution was a switch to New Zealand Kaolin (which contains only 0.15% iron) and VeeGum. The result is dramatically better. However a pinkish color still remained. This made it necessary to add a small amount of blue stain. Now it has the color of cone 10 reduction porcelain! Be careful about substituting that stain. We have found this one flows freely. If the stain you substitute agglomerates during mixing you will get ugly blue specks in your porcelain!

This body pairs with G2931K clear glaze (the fully fritted version of G2931F) and a drop-and-soak firing glaze schedule. Look for a links to that here or google it.

The secrets of this body are thus:
-The 30% frit: Frit is expensive (no normal porcelains contain it because of this). But it makes the impossible possible!
-The NZ Kaolin: The whitest available in the world.
-The VeeGum: Super plastic super-white. Bentone also works.
-The silica for glaze fit and as a structural framework.

As noted, this body will be among the most plastic you have even used (of any kind). But this is only true if it is stiff enough. If you try to use it soft the shrinkage will be much higher and you risk drying cracks.

Caveat 1: This is not an attempt to rival the fired surface of cone 6 Plainsman Polar Ice, it is not as smooth and dense (but it is almost zero porosity). You could, of course, fire higher to produce higher density. But remember, this is frit-ware, warping issues will creep in quickly as temperature is increased. Firing higher than cone 03 will not necessarily produce more strength either. It will produce more fired shrinkage (which is already quite high).

Caveat 2: This frit is slightly soluble. That means that on storage it will change stiffness in the plastic clay or affect the rheology of a casting slip. It can affect plaster molds. And it leave a fuzz on the plaster table as water evaporates leaving the precipitate on the surface (however this is easily scaped away). It is thus best to use all of the clay that you make as soon as possible.

If we were to manufacture this is could cost $100 a box. But before dismissing this think about the advantages of using it for making smaller pieces:
-Fast firing: two or three times a day (as little as 3 hours start to kiln opening).
-The appearance of cone 10R but with far brighter colors.
-High strength (rivaling any other temperature).
-Throw ware ultra thin and light.
-A perfectly fitted ultra-clear glaze that is far cheaper to make than commercial glazes (and works better).
-Dramatic reduction in wear-and-tear on kiln elements and energy usage.
-Remember to factor in the fact that you will be able to charge more for pieces when you calculate clay-cost-per-piece.

A final note: Because this body matures at such a low temperature it needs to be bisqued much lower. You will need to experiment. Consider starting at around 1500F. If ware is not absorbent enough fire lower.

Units-of-measure: I have specified 50 lb bags to fill the needed amount for the NZ kaolin, however it comes in 20kg bags. But you are likely mixing in grams or ounces so just refer to the percentage column.

One more thing. Consider getting an account at, copy and paste the recipes and document all your testing well. And you will get monthly email updates on this another projects.

Batch Ticket Notes

Notes for this ticket.


L3924B Frit-ware porcelain mug with G2931K glaze

The only difference between this and L3924C is the amount of blue stain. This has 0.07% and C has 0.05%. Fired at 03 with G2931K glaze (it is the all-frit version of G2931F). The result is stunning! Fired strength is incredible. It can withstand immersion into icewater from 300F. Glaze is absolutely crystal clear, underglaze is the clearest and brightest I have ever seen! Very pleasant reduction-like blue white color.

Zero3 Porcelain translucency

Zero3 Porcelain as engobe Zero3 Terracotta does not work

3924C on 3724N - cracking badly because the fired shrinkage is 10% vs body of 6%.

L3924B cone 03 porcelain (right) vs. cone 10R body

The mug on the left is a Grolleg Porcelain, fired to cone 10 with G1947U glaze. This body (right) appears greyer on the photo that it actually is. The glaze is G2931F. Admittedly, the Grolleg does has an ice-blue shade that is more pleasant.

G2931K glazed Zero3 Porcelain Mugs

P700 vs. Zero3 vs. Polar Ice

P700 isa Grolleg porcelain fired at cone 10R. Zero3 is a cone 03 fritware body fired at cone 03 oxidation. Polar Ice is a New Zealand kaolin porcelain fired at cone 6 oxidation All are zero porosity and very strong.

Be careful with type and percentage of stain

Normally I use Mason 6336, but the piece on the right in Mason 6300 Mazerine Blue. Obviously that blue is much more potent. So test with your blue stain before making a big batch of the porcelain.

Zero3 Porcelain 10 inch marbled bowl

Glaze is G2931K Zero3 clear. Cone 03 firing.

L3924C, D, E, F compared at cone 03


SHAB - Shrinkage/Absorption

1 94.84 84.16 35.02 35.32 -4.0 5.2% 11.3% 0.9%
2 94.84 83.81 37.08 37.11 -4.0 5.2% 11.6% 0.1%
3 93.58 83.6 34.21 34.24 -3.0 6.4% 10.7% 0.1%
4 93.46 83.32 32.29 32.33 -2.2 6.5% 10.8% 0.1%
5 26.16 26.19 1.0 0.1%

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Zero3 Porcelain - Experimental" id="95860" key="3dqiP2K1" date="2021-03-10" codenum="L3924C" location="BOX48"> <recipelines> <recipeline material="New Zealand Kaolin" amount="227.000" tolerance="" unitabbr="KG"/> <recipeline material="Ferro Frit 3110" amount="300.000" tolerance="" unitabbr="LB"/> <recipeline material="Silica" amount="200.000" tolerance="" unitabbr="LB"/> <recipeline material="VeeGum T" amount="30.000" tolerance="" unitabbr="LB"/> <recipeline material="Mason 6336 Blue Stain" amount="250.000" tolerance="" unitabbr="GM"/> </recipelines> </recipe> </recipes>

Born: 2014-09-19, Modified: 2021-03-10 07:34:04

Zero3 Engobe Recipe

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

Amaco white engobe vs. L3685U 15% white stain

Even with 15% white stain this engobe is not nearly as white (in the raw state) as the Amaco version. Need to experiment more with whiter kaolins and opacifer additions.


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)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Zero3 Engobe Recipe" keywords="For use with the Zero3 body and glaze" id="93335" key="DGKgfZiM" date="2021-02-01" codenum="L3685U1" location="BOX48"> <recipelines> <recipeline material="Nepheline Syenite" amount="10.000" tolerance=""/> <recipeline material="Pioneer Kaolin" amount="42.000" tolerance=""/> <recipeline material="Ferro Frit 3110" amount="25.000" tolerance=""/> <recipeline material="Silica" amount="20.000" tolerance=""/> <recipeline material="National Standard Bentonite" amount="5.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2014-11-04, Modified: 2021-02-01 16:04:10

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 it Worthington Clear predecessor, 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 (this recipe, G2931K, was formulated to have the same chemistry as F but use frits instead). It is crystal clear and super glassy at cone 03.

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. Use 04DSDH as a model.

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. Left: Plainsman Buffstone, contains no talc, fires buff. Center: L212 (about 25% talc). Right: L213 (about 45% talc, fires whiter). Talc raises thermal expansion. The centre glaze is G2931K (Insight-live reports COE 7.4), it fits L215 (also Zero3 porcelain and stoneware). It crazes on Buffstone and shivers on L213 and L212. G2931L has lower expansion (to work on zero-talc porous bodies). G2931H is higher (for talc bodies like L213).

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)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Zero3 K Cone 03 Transparent Glaze" id="95671" key="6FtDbJLN" date="2020-12-02" typecodes="ST" codenum="G2931K" picturebasename=""> <recipelines> <recipeline material="Ferro Frit 3195" amount="25.000" tolerance="" unitabbr="KG"/> <recipeline material="Ferro Frit 3134" amount="33.000" tolerance="" unitabbr="KG"/> <recipeline material="EPK" amount="20.000" tolerance="" unitabbr="KG"/> <recipeline material="Ferro Frit 3249" amount="10.000" unitabbr="KG"/> <recipeline material="Ferro Frit 3110" amount="7.000" unitabbr="KG"/> </recipelines> </recipe> </recipes>

Born: 2006-03-16, Modified: 2020-12-02 07:32:09

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.