Cone 6 Perfect Clear is not quite so perfect

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

This recipe could be improved by using frits instead of Gerstley Borate and Minspar. But even then, it has other issues. There is a better way, see column 3.


Perfect Clear

A well known cone 6 transparent

Code #

G3925

Materials Amt
Minspar 200 40.000
Gerstley Borate 30.000
OM #4 Ball Clay 20.000
Flint Silica (Silica) 10.000

Total:100.00

Auto Unity Formula

CaO 0.51
MgO 0.13
K2O 0.09
Na2O 0.27
(KNaO) 0.37
TiO2 0.02
B2O3 0.51
Al2O3 0.56
SiO2 3.96
Fe2O3 0.01

Ratios

Si:Al: 7.1:1
SiB:Al: 8.0:1
R2O:RO: 0.4:0.6

Expansion

6.9 (Molar:6.8)

LOI

10.8

Notes

*This is a popular transparent cone 6 glaze. We use it for comparing feldspars in-glaze.

While this 10:20:30:40 recipe is convenient, it is much less than "Perfect", we use this as a demo of how such recipes can often be improved using some glaze chemistry.

40% feldspar in a cone 6 glaze is highly unusual. And high feldspar is normally a red-flag for crazing. But this glaze is "rescued" by it 30% Gerstley Borate (GB). GB has a high B2O3 content and that has a low thermal expansion (countering the high expansion of all the sodium/potassium (KNaO) in the feldspar). But 30% GB content means that the slurry will gel badly, only about a 1.35 specific gravity can be achieved (without having a bucket of jelly).

This glaze is guaranteed to have issues with drying cracks, and therefore crawling. It is not just the high water content needed to keep it from gelling, but the added ball clay. GB is plastic, like a clay, 30% is plenty to suspend a glaze, no added clay is needed. But this has 20% highly plastic ball clay also. You could likely dewater the slurry and throw this glaze, like a clay, on a potters wheel!

The low Si:Al ratio produces a less glossy surface than it would if that ratio was higher. To counter that the very high feldspar content is pushing the KNaO levels much higher than typical cone 6 glazes. That is the reason why this is as glossy as it is (while having such a low Al:Si ratio). But again, the high KNaO means issues with crazing on many clay bodies.

The high LOI, 11% which is mainly from from the GB, means gas bubbles will be generated, if they come when the glaze is melting then bubble clouds will appear in the glass.

Pictures

G3925 Perfect Clear on M390, M340

Left: Uses L4441B Minspar subsitute
Right: Uses Minspar (at 40%)
Results are the same. The glaze was a little thicker on the left-top, so was clouding a little.

G3925, G3925A glaze comparison

G3925, G3925A glaze flow comparison

Fired to cone 6. The calculated substitute for Minspar is used in G3925A, 40% of the recipe. The flows are identical.

Untitled

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Perfect Clear" keywords="A well known cone 6 transparent" id="48913" key="QQXYj4Z2" date="2022-03-02" codenum="G3925"> <recipelines> <recipeline material="Minspar 200" amount="40.000" tolerance=""/> <recipeline material="Gerstley Borate" amount="30.000" tolerance=""/> <recipeline material="OM #4 Ball Clay" amount="20.000" tolerance=""/> <recipeline material="Flint Silica" lookup="Silica" amount="10.000" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2013-12-13, Modified: 2022-03-02 14:45:35

Perfect Clear Make-Over #1

Code #

G3925B

Materials Amt
Ferro Frit 3110 15.814
Ferro Frit 3124 23.256
Ferro Frit 3195 23.256
EPK 22.326
Silica 45 Micron (Silica) 11.163
Talc 4.186

Total:100.00

Auto Unity Formula

CaO 0.50
MgO 0.14
K2O 0.03
Na2O 0.34
(KNaO) 0.36
B2O3 0.51
Al2O3 0.55
SiO2 3.94

Ratios

Si:Al: 7.1:1
SiB:Al: 8.1:1
R2O:RO: 0.4:0.6

Expansion

6.8 (Molar:6.8)

LOI

3.5

Cost

0.00 per kg

Notes

*Perfect Clear is tricky for substituting frits to source B2O3 (instead of Gerstley Borate). This is because of the high KNaO level (from all that Minspar). Common frits that source the needed B2O3 also have plenty of KNaO, thus no Minspar is needed here (however that doubles the cost). The frits also oversupply CaO (which both Minspar and GB supplied).

With 22% EPK and no GB to gel it, this will produce a far better slurry to work with.

Will this work? Likely not. A 60% frit recipe is obviously going to melt too much at cone 6, even though the chemistry is the same (there is just too much B2O3 here, a remnant of all the GB in the original). It should have a lot more silica and employ at least some feldspar. It so happens that is what our G2926B recipe is.

Pictures

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Perfect Clear Make-Over #1" id="209682" key="KCL2c2xS" date="2022-10-16" codenum="G3925B"> <recipelines> <recipeline material="Ferro Frit 3110" amount="15.814" tolerance=""/> <recipeline material="Ferro Frit 3124" amount="23.256" tolerance=""/> <recipeline material="Ferro Frit 3195" amount="23.256" tolerance=""/> <recipeline material="EPK" amount="22.326" tolerance=""/> <recipeline material="Silica 45 Micron" lookup="Silica" amount="11.163" tolerance=""/> <recipeline material="Talc" amount="4.186" tolerance=""/> </recipelines> </recipe> </recipes>

Born: 2013-12-13, Modified: 2022-10-16 12:26:55

Cone 6 Clear Glossy Base

Code #

G2926B

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%

Total:110.10

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%

Ratios

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

Expansion

6.4 (Molar:6.3)

LOI

3.0

Cost

0.00 per kg

Notes

*The base recipe used by production at Plainsman Clays.

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.

Some clay bodies having very low silica content may craze this, in this case consider using the G1214U recipe.

Pictures

URLs

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="hrevoJjc" date="2023-11-13" 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: 2023-11-13 15:28:34