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How to fix Gerstley Borate-based Worthington Cone 04 Clear
These popular base recipes for both low and medium temperature call for 50% or more Gerstley Borate. How can frits be used instead?
Project Name Gerstley Borate Transparent Glossy Base Glaze Recipes Project Codenumber UnAssigned Notes Gerstley Borate was found in amounts up to 50% of the total recipe, creating very fluid base glazes (at both low and middle temperatures). Depending on the amount of feldspar present, recipes had from 5-20% kaolin (the two together supplying the needed Al2O3). Silica was almost always present, typically 20-30%. |
50:30:20 Gerstley Borate Cone 6 base
Total:100.00 Auto Unity Formula
Notes *This is recipe has been around for a long time. It is the base for many others, mainly because of its high melt fluidity (e.g. Butterscotch (Rust) added: 4% rutile, 4% tin oxide and 1% lithium carboante. Pictures G2826A vs G2826A1 low test A1 supplies boron using frit 3134. G2826A Gerstley Borate 50:30:20 base as jelly G2826A on M390 - lots of boron blue You might think this looks nice. But it comes at a cost (bubbling, jelling, running, cracking on drying, crawling). Boron blue is considered a glaze fault. Fired at 1700F G2826A 50:30:20 GB Fired at 1700F XML (to paste into Insight) <?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="50:30:20 Gerstley Borate Cone 6 base" id="67237" key="HQAAfacg" date="2024-10-02" codenum="G2826A" picturebasename=""> <recipelines> <recipeline material="Gerstley Borate" amount="50.000" tolerance=""/> <recipeline material="EPK" amount="20.000" tolerance=""/> <recipeline material="Silica" amount="30.000" tolerance=""/> </recipelines> </recipe> </recipes> Born: 2000-04-18, Modified: 2024-10-02 18:51:28 |
50:30:20 Frit 3134 base (fixed)
Total:100.00 Auto Unity Formula
Notes *The 77C04E base (50:30:20 Frit 3134:silica:kaolin) has multiple issues as an alternative to the original 50:30:20 Gerstley Borate G2826A recipe. This addresses those. Pictures G2826A vs A1 50:30:20 base flow test The flow of the fritted version (on the right) has no boron-blue, more surface tension, less LOI disruption. Fluidity is only a little less even though this has less boron. G2826A, G2826A1 on M340, M370 Boron blue gone on the fritted version. G2826A vs G2826A1 demos Gerstley Borate vs Frits to source boron If a better quality functional glaze is needed then the G2826A1 fritted version on the right is much better. That being said, many people seek the visual character of the one on the left. Perhaps a mix of the two could reduce some of the working and technical issues with the G2826A version. G2826A vs G2826A1 low test A1 supplies boron using frit 3134. G2826A3 vs G2826A1 - Fired to 1700F The G2826A1 employs a frit, the G2826A2 (left) Gillespie Borate. XML (to paste into Insight) <?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="50:30:20 Frit 3134 base (fixed)" id="223705" key="q1H4PnLh" date="2023-09-08" codenum="G2826A1" picturebasename=""> <recipelines> <recipeline material="Ferro Frit 3134" amount="29.000" tolerance=""/> <recipeline material="EPK" amount="19.000" tolerance=""/> <recipeline material="Fusion Frit F-69" amount="20.000" tolerance=""/> <recipeline material="325 mesh silica" lookup="Silica" amount="22.000" tolerance=""/> <recipeline material="Wollastonite" amount="10.000" tolerance=""/> </recipelines> </recipe> </recipes> Born: 2000-04-18, Modified: 2023-09-08 03:23:36 |
Worthington Cone 06-2 Clear Gelling, High LOI, Gerstley Borate difficult to sub, High Boron
Total:100.00 Auto Unity Formula
Notes *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). Pictures 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. 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. 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 Testdata 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="8a33B96b" date="2023-04-13" codenum="G2931" picturebasename=""> <recipelines> <recipeline material="Gerstley Borate" amount="55.000" tolerance=""/> <recipeline material="EPK" amount="30.000" tolerance=""/> <recipeline material="Silica" amount="15.000" tolerance=""/> </recipelines> </recipe> </recipes> Born: 2014-03-17, Modified: 2023-04-13 22:30:05 |
Zero3 K Cone 03 Transparent Glaze
Total:95.00 Auto Unity Formula
Notes *This recipe improved on the popular Worthington Gerstley-Borate-based low fire clear recipe. It targeted cone 03 to work best on Zero3 stoneware and porcelain. To fire lower (cone 06-04), consider G1916Q (or derivatives) instead. Batch Ticket Notes These notes were entered in the notes panel under "Batch Ticket Notes" Pictures G2931K on Zero3 Stoneware Fired cone 03. Body is Zero3 stoneware. 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 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. 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. G1916Q (left) vs G2931K (right) at cone 04 On a terra cotta body, the G1916Q is performing better, there are less micro bubbles. URLs How to tune the thixotropy of a glaze How to convert a d..o a brushing glaze Typecodes 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="v7ejvcKB" date="2023-05-03" typecodes="ST" codenum="G2931K" picturebasename=""> <recipelines> <recipeline material="Ferro Frit 3195" amount="25.000" tolerance=""/> <recipeline material="Ferro Frit 3134" amount="33.000" tolerance=""/> <recipeline material="EPK" amount="20.000" tolerance=""/> <recipeline material="Ferro Frit 3249" amount="10.000" tolerance=""/> <recipeline material="Ferro Frit 3110" amount="7.000" tolerance=""/> </recipelines> </recipe> </recipes> Born: 2006-03-16, Modified: 2023-05-03 20:54:14 |