Zero3 Clear Glazes With Firing Schedule

Share form Insight-live.com (Lab Documentation and Calculation System) by Digitalfire

See Also: Zero 3 L & K Glazes Compared to the Worthington Clear Original

The first column, G2931L, is a low expansion, non-talc and non-vitreous bodies. The second is K for moderate talc and Zero3 porcelain and stoneware. Third is H high expansion (for high talc bodies).


Zero3 K Low Expansion Variant

Code #

G2931L

Materials Amt Units
Ferro Frit 3195 19.000 KG 19.10%
EPK 10.000 KG 10.05%
Ferro Frit 3249 19.000 KG 19.10%
Fusion Frit F-524 49.000 KG 49.25%
Zinc Oxide 2.500 KG 2.51%

Total:99,500.00 (R)

Auto Unity Formula

BaO 0.02
CaO 0.39
MgO 0.20
K2O 0.05
Na2O 0.12
(KNaO) 0.16
ZnO 0.10
SrO 0.12
B2O3 0.77
Al2O3 0.44
SiO2 2.82

Si:Al Ratio

6.4:1

SiB:Al Ratio

8.1:1

Calculated
Expansion

6.3

LOI

1.5

Cost

0.10 per kg

Notes

This is a low-expansion version of the Zero3 Clear glaze (code G2931K), originally developed from the Worthington Clear Gerstley Borate based recipe. While G2931K fits the vitreous Zero3 porcelain and non-vitreous bodies containing talc (like Plainsman L212, L215), it crazes on others (e.g. Plainsman TerraStone, BuffStone, L210). This version drops its expansion drastically, from 7.4 down to 6.3 (by adding ZnO, ZrO and increasing MgO and SiO2).

Since the thermal expansion of this is higher than the original Wothington Clear and the L version is lower, it is thus possible adjust thermal expansion of either recipe by adding some of the other (to deal with shivering or crazing on almost any low fire body).

Do not try to use this with too little water. Mix it to 1.43 specific gravity and add vinegar or Epsom salts to gel it so that it stops moving (after vigorous stirring) in 2 or 3 seconds. When mixed right it applies very well to low or high porosity bisque (in a very thin layer if needed), it does not drip or move.

The soak:soak:slowdrop firing schedule is critical to a defect-free surface.

Pictures

G2931L and K clear glazes (for non-talc, talc bodies)

These pieces have underglaze decoration with a covering clear glaze. But the glazes are different. The G2931L (left) has a lower thermal expansion (to prevent crazing on non-talc bodies like this). The G2931K glaze fits the terra cotta because the latter contains significant talc (to raise its expansion to fit commercial glazes better). If you switched these glazes the left mug would craze the glaze and the right would would shiver it off in flakes.

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.

Typecodes

ST-Untitled typecode

Alternate Code Number:GS04-1

Born: 2006-03-16, Modified: 2017-09-17 21:59:08

Zero3 K Low Fire Transparent Glaze

Code #

G2931K

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 Ratio

6.1:1

SiB:Al Ratio

7.9:1

Calculated
Expansion

7.4

LOI

3.1

Cost

0.20 per kg

Notes

This recipe converts the popular Worthington Gerstley-Borate-based low fire clear recipe into something that 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), does not craze or shiver (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. The results are excellent, actually stunning! 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). Links to them can be found below. 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 perfectly crystal clear, no commercial glaze can match your own fitted one. And you can make make your own brushing versions (see link below).

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"

URLs

Glaze fit test

How to tune the thixotropy of a glaze

How to convert a d..o a brushing glaze

Pictures

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).

G2931K Fritted version of G2931F - Cup

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 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

Typecodes

ST-Untitled typecode

Alternate Code Number:GS04-1

Born: 2006-03-16, Modified: 2017-10-08 20:25:01

Zero3 High Expansion Variant

Code #

G2931H

Materials Amt Units
Ferro Frit 3195 30.000 KG 30.00%
Ferro Frit 3134 33.000 KG 33.00%
EPK 20.000 KG 20.00%
Ferro Frit 3249 KG 0.00%
Ferro Frit 3110 17.000 KG 17.00%

Total:100,000.00 (R)

Auto Unity Formula

CaO 0.60
K2O 0.02
Na2O 0.38
(KNaO) 0.40
B2O3 0.65
Al2O3 0.37
SiO2 2.59

Si:Al Ratio

6.9:1

SiB:Al Ratio

8.7:1

Calculated
Expansion

8.0

LOI

3.0

Cost

0.19 per kg

Notes

This is a high-expansion version of the Zero3 Clear glaze (code G2931K), originally developed from the Worthington Clear Gerstley Borate based recipe. While G2931K fits the vitreous Zero3 porcelain and stoneware and also non-vitreous low-talc bodies (like Plainsman L212, L215), it shivers on high-talc bodies (e.g. Plainsman L213). That means that this G2931K variant is the most similar to commercial low fire glazes (which are designed to fit high-talc bodies).

This version increases the thermal expansion of Zero3 K glaze from 7.4 to 8.0 (by adding increasing KNaO at the expense of MgO, ZnO).

Do not try to use this with too little water. Mix it to 1.43 specific gravity and add vinegar or Epsom salts to gel it so that it stops moving (after vigorous stirring) in 2 or 3 seconds. When mixed right it applies very well to low or high porosity bisque (in a very thin layer if needed), it does not drip or move.

The soak:soak:slowdrop firing schedule is critical to a defect-free surface.

Pictures

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.

L212. L2931K shivering. L2931H is good.

Typecodes

ST-Untitled typecode

Alternate Code Number:GS04-1

Born: 2006-03-16, Modified: 2017-09-17 22:01:53

Firing Schedule Name

Cone 03 hold-rise-drop-hold

Degrees (Fahrenheit or Celcius)

Unspecified

Schedule Type

Rate

Start Time and Temperature

8:01 am (no temperature specified)

Program

Step Degrees/Hr Temperature
Monitor
Hold
Time
Accumulated
hrs:min
Time Note
1 400 240 60 1:36 9:37 am
2 800 1850 30 4:06 12:07 pm
3 108 1950 10 5:11 1:12 pm
4 500 1850 30 5:53 1:54 pm

Notes

The firing can start and finish within your working day. Step 2 can often be done as fast as your kiln will go. We are done cold-to-cold in three hours.

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 slow 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.