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Worthington Clear with Ulexite:Wolly
This is a lower expansion version of G2931K, an ultra-clear for porcelain and talc bodies at low fire. This sacrifices some surface brilliance for the low thermal expansion. The chemistry of this recipe cannot be produced using common frits, the Ulexite is essential (the boron high).
Links with Schedules
Ulexite Worthington Clear to cone 02
No pinholes, thin application. Some bubbles. This was fired to temperature and soak 10 minutes (and cool of 100 degrees and soak there would have yielded even better results). Cone 03 and 02 do produce a more brilliant result than cone 04.
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.
Ulexite Worthington clear cone 02
This is a terra cotta stoneware body, the body contains enough frit to produce 1% porosity at cone 02. Although it appears to work well, it is under too much compression because its thermal expansion is too low. We noted a tendency to shiver on the rims of mugs, especially with the white engobe present.
Worthington Original vs. Ulexite varitation flow test
Gas generation during melt is obviously more active in the Gerstley Borate version (left) than in the Ulexite version (right). This is fired to cone 03.
Entrained bubbles in Ulexite Worthington
16x photo of a 10 gram glaze ball melted down onto a tile, it was fired to cone 03. This has both the large and small bubbles populations.
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.
G2931B and F fit different bodies
The fritted vitreous body on the left shivers using G2931B. The same body (having the same white slip (G3685U) does not shiver the G2931F version of the glaze (it has more KNaO).
Ulexite Worthington Clear - Low Expansion
This is an even lower expansion version of G2931B (see its notes for more information, especially about mixing with water and specific gravity). This is only needed if 2931B crazes.
Terra cotta and thermal shock
This terra cotta cup is glazed with G2931G clear glaze and fired at cone 03. It survives 25 seconds under direct flame against the sidewall before a crack occurs. Typical porcelains and stonewares would survive 5-10 seconds!
P6318 Terrastone with G2931G Clear Glaze cone 03
G2931G clear shivering on 3724N1 (fritted terra cotta) at cone 03
G2931F (left), G2931G (right) on buffstone
Cone 03. Did boiling water, ice water test on both. F crazes (notice the piece is waterlogged). G does not. Buffstone has a high porosity at this temperature so glazes must fit well.
P580 Pioneer cone 10R bisqued with 2931F and G glazes
F crazes. G does not. Both need to be applied thicker.
P580 with cone 03 clear vs cone 10 clear
G2931G clear on cone 10R bisqued piece (left).
Firing Schedule Name
Cone 03 soak-soak-slow cool
Degrees (Fahrenheit or Celcius)
Start Time and Temperature
8:01 am (no temperature specified)
The firing can start and finish within your working day. Step 2 can often be done as fast as you kiln will go.