Lowering the Thermal Expansion of G2926B

Share from Insight-live.com (Lab Documentation and Calculation System) by Digitalfire. https://digitalfire.com

These are two recipes that we have found reduce the COE of the popular G2926B.

Cone 6 Clear Glossy Base

Code #


Materials Amt
Nepheline Syenite 18.300 16.62%
Ferro Frit 3134 25.400 23.07%
EPK 19.600 17.80%
Vansil W-30 Wollastonite 6.900 6.27%
Silica 325 mesh (Silica) 37.600 34.15%
Silverline 303 Talc 2.300 2.09%


Auto Unity Formula + Analysis

CaO 0.59 7.49%
MgO 0.09 0.78%
K2O 0.04 0.83%
Na2O 0.28 3.99%
(KNaO) 0.32
TiO2 0.00 0.07%
P2O5 0.00 0.04%
B2O3 0.33 5.26%
Al2O3 0.48 11.05%
SiO2 4.96 67.36%
Fe2O3 0.00 0.18%


Si:Al: 10.3:1
SiB:Al: 11.0:1
R2O:RO: 0.3:0.7


6.4 (Molar:6.3)




0.17 per kg


*The base recipe used by production at Plainsman Clays. This is our production batch, 500kg.

There are lots of pages and pictures online about this recipe and stain-added versions (e.g. at digitalfire.com and plainsmanclays.com). The page at Plainsman Clays has mixing and usage information.

This recipe has proven to work very well as a general purpose cone 6 transparent. It works best if ball milled (for lowest possible thermal expansion, best surface quality, least surface defects, best clarity). Unlike many others, this has very high SiO2, that means the best possible durability. It also has significant Al2O3, further contributing to stability of the melt and glass.

Although EP Koalin is used here, we have produced even better results using Grolleg and New Zealand kaolins. Using all three it is possible to get a slurry with excellent suspension and applications properites if attention is paid to the thixotropy.

This fits most Plainsman Clays bodies (and those of other manufacturers). But it does not fit Plainsman P300, a cone 6 whiteware, unless ball milled or a 325mesh silica is used.



Technical informat..at digitalfire.com

Mixing, adjustment..PlainsmanClays.com

Alternate Code Number:MG6CG

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 6 Clear Glossy Base" id="180072" key="tcwq8ubk" date="2023-04-17" codenum="G2926B" picturebasename=""> <recipelines> <recipeline material="Nepheline Syenite" amount="18.300" tolerance=""/> <recipeline material="Ferro Frit 3134" amount="25.400" tolerance=""/> <recipeline material="EPK" amount="19.600" tolerance=""/> <recipeline material="Vansil W-30 Wollastonite" amount="6.900" tolerance=""/> <recipeline material="Silica 325 mesh" lookup="Silica" amount="37.600" tolerance=""/> <recipeline material="Silverline 303 Talc" amount="2.300" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2014-05-15, Modified: 2023-04-17 10:48:54

G2926B Reduced COE (Li2O)

Code #


Materials Amt
Spodumene 11.000
Fusion Frit F-524 15.000
Ferro Frit 3134 15.000
EPK 18.000
Wollastonite 6.000
Silica 32.000
Silverline Talc (Talc) 3.000


Auto Unity Formula

CaO 0.55
Li2O 0.13
MgO 0.11
K2O 0.02
Na2O 0.13
(KNaO) 0.15
SrO 0.05
B2O3 0.33
Al2O3 0.50
SiO2 5.00


Si:Al: 10.0:1
SiB:Al: 10.7:1
R2O:RO: 0.3:0.7


5.6 (Molar:5.5)




0.73 per kg


*Remember, the first thing to try to reduce the thermal expansion of G2926B is using 325 mesh silica (or ball milling the slurry). That alone will assure that all silica in the recipe actually goes into the melt, that means that the physical thermal expansion will be as low as the calculated one suggests it should be. If that is not enough, then try this recipe. Use 325 silica in this one also to get the lowest possible expansion.

This is the best of a series of tests to lower the thermal expansion of G2926B. Separate trials of substituting ZnO, SrO, Li2O for KNaO were tried (in each the brilliant surface was being marred by an orange peel like surface). This version is a hybrid, diversifying fluxes by adding Li2O and SrO. It sources SrO from Frit 524 and Li2O from Spodumene.

The calculated expansion is dramatically lower, 5.6 vs. 6.4. This should thus be much more resistant to crazing. Of course, there is an issue: Spodumene introduces bubbles into the slurry in the bucket (washing it before use could solve this). Color response might also be different.


G2926B vs J shock test

There was no crazing at 320F, but at 340F 2926B has five cracks and this has one at the edge.

It is interesting that 2926B has performed differently in different firings in this test.

2926J on P380

The surface is brilliant and clear.

G2926B vs J Cone 6 Fluidity

G2926J is flowing a little more. Fired character is very similar to B.

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="G2926B Reduced COE (Li2O)" id="76267" key="FrLRypAM" date="2021-06-02" codenum="G2926J"> <recipelines> <recipeline material="Spodumene" amount="11.000"/> <recipeline material="Fusion Frit F-524" amount="15.000"/> <recipeline material="Ferro Frit 3134" amount="15.000"/> <recipeline material="EPK" amount="18.000"/> <recipeline material="Wollastonite" amount="6.000"/> <recipeline material="Silica" amount="32.000"/> <recipeline material="Silverline Talc" lookup="Talc" amount="3.000"/> </recipelines> </recipe> </recipes>

Born: 2014-02-19, Modified: 2021-06-02 13:55:51

G2926B Reduced COE (MgO)

Code #


Materials Amt
Nepheline Syenite 20.131
Ferro Frit 3134 10.475
Fusion Frit F-69 10.311
EPK 12.439
Wollastonite 11.293
Silica 35.352


Auto Unity Formula

CaO 0.60
MgO 0.15
K2O 0.04
Na2O 0.21
(KNaO) 0.26
B2O3 0.34
Al2O3 0.46
SiO2 4.97


Si:Al: 10.7:1
SiB:Al: 11.5:1
R2O:RO: 0.3:0.7


6.1 (Molar:6.0)




0.12 per kg


*This is an adjustment to G2926B to reduce its thermal expansion. However, before trying this, we recommend ball milling the G2926B or using 325 mesh silica in that recipe. Only if those do not work, then try this (use 325 silica in this one also, the fine particles assure all of it melts).

This recipe increases MgO at the expense of KNaO. Even though MgO levels are quite high, no loss of gloss has happened! The effect on lowering the thermal expansion is dramatic.

With 10% added zircopax this produces a white of even lower thermal expansion. We have subjected various Plainsman P300 pieces (a difficult-to-fit-glazes-to body) to 300F:IceWater thermal shocking and there is no crazing. However that much zircon can induce crawling issues, we have found that 3% tin and 5% zirocpax is better.

For use as a transparent consider adding 2% zircopax. That is insufficient to opacify but the zircon does act as a fining agent to remove microbubbles and make the glass more transparent.

Ferro Frit 3249 can be substituted for Fusion F-69 (although F-69 is more reliable for ceramics). Likely any kaolin can be used.

Although there is only 12.5% kaolin this will suspend well if the slurry is thixotropic. In our initial mix 5000g water and 6000g powder produced 1.47SG. That was very watery so we added about 10g of Epsom salts to gel it.


G2926S after 300F:IceWater test on P300

No crazing after the test.
The transparency and clarity of the glass is great, this looks very promising.

P300 after 300F:IceWater test

S is not crazing after two days. B crazing in the cold water.

M370 with G2926S, G2926B inside


XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="G2926B Reduced COE (MgO)" id="131969" key="nQ6p1cqN" date="2022-08-30" codenum="G2926S"> <recipelines> <recipeline material="Nepheline Syenite" amount="20.131" tolerance=""/> <recipeline material="Ferro Frit 3134" amount="10.475" tolerance=""/> <recipeline material="Fusion Frit F-69" amount="10.311" tolerance=""/> <recipeline material="EPK" amount="12.439" tolerance=""/> <recipeline material="Wollastonite" amount="11.293" tolerance=""/> <recipeline material="Silica" amount="35.352" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2014-02-19, Modified: 2022-08-30 07:51:29