Share from Insight-live.com (Lab Documentation and Calculation System) by Digitalfire
This is a popular glaze but flawed in several ways. You can do better using these alternatives. Frits are needed and more expensive up front, but you'll save money later.
Worthington Cone 06-2 Clear
Gelling, High LOI, Gerstley Borate difficult to sub, High Boron
Auto Unity Formula
This recipe is a common Gerstley Borate clear base used from 04 all the way to cone 6! At higher temperatures the recipe trends toward less kaolin to more silica and a little less GB (e.g. 50:20:30).
2931 vs 2931b
On Plainsman L215 cone 02 the original base Worthington Clear has gone on very thin on sides of mug (because of the low specific gravity necessary to prevent it from gelling it is very difficult to get it on thick enough). The fired surface is clear but not as glossy. On the rim it has bubbles. The Ulexite version (G2931B) is glossier, and went on thicker because the slurry is so much easier to use. This glaze is not recommend for L215, the latter contains talc that increases its thermal expansion, putting too much squeeze on this glaze.
Worthinton Clear at cone 01
On a terra cotta clay at this temperature was has stoneware properties. The fired surface is good.
Worthington Clear vs. Fritted Clear
Worthington (right) flows even better than the fritted glaze and does not have any more entrained bubbles even though it has an LOI of 20%. This is likely because its melting history and behavior is such that its ability handle gases of decomposition from the body and its own materials is so much better.
Entrained bubbles in Worthington Clear
This is a 16X closeup of flow test (10 gram ball melted down onto a tile) that concentrates bubbles. There are high populations of large and tiny ones. The larger ones are from the Gerstley Borate, the tiny ones from the kaolin.
GB vs Ulexite Clear glaze bubbles
These are 10 gram balls fired down onto tiles at cone 04 to compare melt fluidity and bubble populations in three clear glazes. Larger bubbles are better, they break at the glaze surface and heal. Tiny ones produce cloudiness.
Worthington Clear the next day
Even though this has a low specific gravity and is deflocculated with darvan, the next day it is still jelly. Impossible to use unless more Darvan is added, who knows where that will go!
G2922G, G2931 flow tests
SHAB - Shrinkage/Absorption
LDW - LOI/Density/Water Content
XML (to paste into Insight)
<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Worthington Cone 06-2 Clear" keywords="Gelling, High LOI, Gerstley Borate difficult to sub, High Boron" id="56711" key="qBgRC24J" date="2017-09-05" codenum="G2931" picturebasename=""> <recipelines> <recipeline material="Gerstley Borate" amount="55.000"/> <recipeline material="EPK" amount="30.000"/> <recipeline material="Silica" amount="15.000"/> </recipelines> </recipe> </recipes>
Zero3 K Low Fire Transparent Glaze
Auto Unity Formula
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.
Batch Ticket Notes
These notes were entered in the notes panel under "Batch Ticket Notes"
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
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.
G2931F vs G2931K fritted - terra cotta mugs cone 03
F was the Ulexite-fluxed version of this recipe.
G2931F vs G2931K flow test
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.
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 need 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 but only a little crazing after a year.
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 Low Fire Transparent Glaze" id="95671" key="7MgzDWoi" date="2018-12-06" typecodes="ST" codenum="G2931K" picturebasename=""> <recipelines> <recipeline material="Ferro Frit 3195" amount="25.000" unitabbr="KG"/> <recipeline material="Ferro Frit 3134" amount="33.000" unitabbr="KG"/> <recipeline material="EPK" amount="20.000" 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>
524 UltraClear - Cone 04 to 1
Auto Unity Formula
I developed this for cone 04 to fit as many clay bodies (without crazing) as possible (my Zero3 clear works well on specific bodies but does not melt enough at cone 04 and it's thermal expansion is too high to fit some bodies). I am developing a recipe for a terracotta casting body at the same time as this and I am working to make it compatible also.
Mike ODonnell and Fusion Frits says many customers use F280 and F38. He suggested F5 might be most similar to this. But I found that F524 was by far the closest.
G3879 on Plainsman L210, L215 at cone 04
These are 42 mesh low fire bodies. They normally have issues with pinholing but using this glaze the results are stunning. The L210 contains no talc, the L215 has 10%, yet this glaze does not craze on either one.
Melt fluidity comparison with #1 commercial clear
We tested half-a-dozen commercial clears and found G3859 to be the best all-around one. This one has a very similar melt fluidity.
G3879 Clear glaze on Plainsman L211 - Cone 04
Glossy, crystal clear, no crazing! And this is a 42 mesh body containing zero talc.
G3878 has a high surface tension
As can be seen in the way it has melted here.
G3879 on SIAL 25F, Plainsman J2, L4170 TerraCotta
These are very different bodies. The leftmost contains talc to raise the thermal expanison to help prevent crazing with commercial glazes. The center one contains nepheline syenite (for the same purpose). The terra cotta on the right is just Redart and ball clay. This glaze fits are all three!
Sial 10F, 25F with G3879 clear glaze at cone 03
G3879 Clear on L4170 TerraCotta Casting
The clear glaze is G3879. The white on the outside of the one on the left has 10% added zircopax. The overglaze colors are Spectrum Majolica colors.
G3879 with 5% Tin Oxide on SIAL 10F
When mixing Tin (as an opacifer), it is very important to mix it well. The one on the left was mixed poorly (at high speed with my propeller mixer but not for long enough). The one on the right was mixed much better and so produces better opacity. Tin is expensive so this is important.
G3879 on Plainsman Buffstone - cone 04
Buffstone is an entry-level low-price body not intended to fit commercial glazes. Yet the glaze fits! And without any surface defects.
G3879 Zircon White on SIAL 25F, 10F - cone 03
10% zircopax has been added. It is melting well so the percentage could be increased for great opacity on red burning bodies.
G3879 at cone 1 on SIAL 10F, 25F
Crystal clear, no running. Perfect!
GBMF test on G3879 at cone 1
It is not running and flowing nearly as much as expected. The melt surface tension holds it in place, so it should be able to fire to cone 2 and beyond.
G3879 on terra cotta at cone 04, 02, 1
This is on the L4170 body, it is a lighter firing product, 25F, from SIAL.
B - Tin White
XML (to paste into Insight)
<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="524 UltraClear - Cone 04 to 1" id="154451" key="KXpA9u4n" date="2019-05-16" codenum="G3879"> <recipelines> <recipeline material="Fusion Frit F-524" amount="850.000"/> <recipeline material="Fusion Frit F-69" amount="40.000"/> <recipeline material="EPK" amount="90.000"/> <recipeline material="Silica" amount="45.000"/> </recipelines> </recipe> </recipes>