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Ravenscrag Cone 6 Clear Glossy Base

Code: GR6-A
Modification Date: 2018-04-28 22:18:47
Member of Group: RV6

This Plainsman Cone 6 Ravenscrag Slip base is just the pure material with 20% added frit to make it melt to a glossy natural clear.

MaterialAmount
Ravenscrag Slip50.0
Ravenscrag Slip 1000F Roast30.0
Ferro Frit 313420.0
 100.00  

Firing Schedule

Rate (F)Temp (F)Hold (Min)Step
100220601
300173302
1082195153
1502095304

Notes

This is the base cone 6 Ravenscrag recipe, it fires as a transparent glossy. It has an addition of the most common North American borate frit, enough to produce a good glass at cone 6. Most other glazes based on Ravenscrag use this as a starting point (although they might substitute the frit for another).

The character of this is not the same as transparent glazes made from materials like feldspar, kaolin, silica, wollastonite and frit. This is a natural clay material having some iron content and particles you can feel (up to 42 mesh). So it forms a less sterile glaze, one having some variegation, fine speckle and slight blush or amber coloration. It is most glossy at a complete cone 6 (for a lower temperature you may need to increase the frit a little).

As a transparent, this glaze it is best suited for use on light-burning stonewares (e.g. Plainsman M340). On whiter porcelains it will not fire to a sufficiently transparent glass. For porcelains or white stonewares consider using G2926B or G3806C instead. On darker clay bodies this recipe may fire too cloudy. Is has a low enough thermal expansion to fit most bodies, but if it does craze consider substituting the Ferro Frit 3195.

As noted, this is a base recipe, well suited to additions of opacifiers, variegators and colors. Add zircopax to get a white (about 10%). The white produced will be somewhat variegated (non toilet-bowl-like). If you want variation with thickness to highlight edges of contours use a lower percentage of zircopax. For even better variegation, add some titanium dioxide (1-2% to a mix already containing 6-8 zircopax).

You can also add colorants and variegators (with or without opacifier). If colorant additions affect melt fluidity, add or reduce the frit content to compensate.

If you get cracking of the glaze during drying, increase the calcine clay at the expense of raw clay.

Roasting Ravenscrag Slip instead of calcining

Roasting Ravenscrag Slip instead of calcining

This is the Ravenscrag Slip I used to calcine at it 1850F (about 10lbs in a bisque vessel). I am now roasting it to 1000F instead, this produces a smoother powder, less gritty. I hold it for 2 hours at 1000F to make sure the heat penetrates. It is not actually calcining, since not all crystal water is expelled, so we call it "roasting". Why do this? Ravenscrag Slip is a clay, it shrinks. If the percentage is high enough the glaze can crack on drying (especially when applied thickly). The roast does not shrink. The idea is to tune a mix of raw and roast Ravenscrag to achieve a compromise between dry hardness and low shrinkage. Technically, Ravenscrag losses 3% of its weight on roasting so I should use 3% less. But I often swap them gram-for-gram.

Cone 5R mug with GR6-A Ravenscrag glaze

Cone 5R mug with GR6-A Ravenscrag glaze

Ravenscrag Slip at cone 5R and 10R

Ravenscrag Slip at cone 5R and 10R

Cone 5 GR6-A glaze at cone 5R on Plainsman M340 (left) and pure Ravenscrag Slip at cone 10R on H550 (right).

Ravenscrag Slip transparent and Alberta Slip blue glazes by Tony Hansen

Ravenscrag Slip transparent and Alberta Slip blue glazes by Tony Hansen

The mug is the buff stoneware Plainsman M340. Firing is cone 6. On the inside is the GR6-A Ravenscrag transparent base glaze. The outside glaze is GA6-C Alberta Slip rutile blue on the outside. The transparent, although slightly amber in color compared to a frit-based transparent, does look better on buff burning stoneware bodies this.

Out Bound Links

In Bound Links

XML to Paste Into Insight

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By Tony Hansen




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