G1214Z Calcium Matte Cone 6 base glaze recipe

Cone 6 Calcium Matte Base Glaze

Total:105.00

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Notes

*Because this was shrinking too much on drying (causing cracking), this recipe was changed in Mar 2019 (using code number G1214Z1) from 37 EPK to 20 EPK and 13 calcined kaolin (although 20+13 does not equal the original 37, it is correct because the calcined version loses less weight on firing). If unavailable, you can make your own calcined kaolin by roasting the powder in a container in a bisque firing.

This is a calcium matte (as opposed to magnesia matte). As such, it develops its visual effect by the crystallization of calcium silicates (which depends on the melt being quite fluid, or runny). A fortunate side effect of this mechanism is that additions of colorants and opacifiers can produce very interesting visuals that vary with thickness and firing cooling rate (which gets potters excited but which industry avoids because of the difficulty in maintaining consistency). There is an implication of this: Uneven thickness with this produces variations in the fired product (e.g. runs are very visible).

The spirit of this recipe originally was to demonstrate the main difference in the chemistry between a matte and glossy glaze, the SiO2:Al2O3 ratio (and how it can be changed to adjust the degree of matteness of a glaze). It was the product of a training course adjusting the chemistry of a glossy as a use-case for early versions of Digitalfire Insight chemistry software during the early 1980s). That recipe jumped from computer screens to actual use and has been employed around the world since by artist potters and even industry (especially tile).

Higher levels of MgO (as opposed to the CaO in this one) produce the other main type of true matte glaze (also well-melted yet matte), the surface of these is "wavy" that imparts a silky feel (as opposed to this calcium matte which has a smooth-feeling surface). Consider testing the G2934 MgO-matte recipe beside this one to determine which is best in your application. As with all mattes, be sure to control the rate of cooling in production firings (and match it to that done during testing) to get the intended degree of matteness. Remember that you can adjust the chemistry to produce more or less mattness (by lowering and raising the SiO2:Al2O3 ratio). Or you can blend in a gloss glaze base.

Cutlery marking can be an issue with this type of glaze, especially for slower cooling kilns (where more crystallization occurs).

Because the high kaolin content can cause excessive drying shrinkage we adjusted this recipe in 2019 to code G1214Z1, that recipe employs a mix of raw and calcined kaolin to supply the oxides.

Pictures

Felt glaze variation with G1214Z on thick

3/8/2009 on ragingbowl's blogspot is getting this effect with this base?

G1214Z Cone 6 Base Matte Transparent Glaze vs 2928C

Despite being a matte this glaze is well melted.

3 opacifiers on Coffee Clay, M390 in G1214Z

G1214Z2 on M340, M390 at cone 6

Cone 6 Calcium Matte v2

Total:101.00

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Notes

*This is an adjustment to the original G1214Z recipe. The chemistry of this is the same, but the 37 raw kaolin in the original has been split to a combination of raw:calcined kaolin to reduce drying shrinkage (preventing cracking as it dries and crawling during firing). If unavailable, you can make your own calcined kaolin by roasting the powder in a container in a bisque firing.

For 3000 grams we use 2600 water to get 1.45 specific gravity and good flow properties (no Epsom salts should be needed to gel the slurry, it is naturally thixotropic).

Pictures

3 opacifiers on Coffee Clay, M390 in G1214Z

G1214Z2 on M340, M390 at cone 6

G1214Z at cone 6 with 10% Zircopax and 5% tin oxide

The body is Plainsman M390. The firing schedule is Plainsman PLC6DS. The tin is on the right.

Cone 6 Calcium Matte + TiO2

Total:106.00

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Notes

*For the brushing version: 440 water, 340 powder, 5 CMC, 5 Veegum. Produced very nice brushing glaze.

Used F621/19 frit (it is the Fusion Frits equivalent to Ferro 3124).

Pictures

G1214Z2 on M390 at cone 6

G1214Z2 on M340, M390 at cone 6

G1214Z2 fired on brown body at cone 6

Three coats brushed on. The coverage is very good. Not as much blue as last time, this could be because the body is not as red (supplying iron oxide). It is likely more blue could be achieved by substituted some or all of the titanium for rutile.

G1214Z2 thin and thick on M390 at cone 6

G1214Z2 brushed-on light and dark clay bodies

Thinner application on left. Fired at cone 6 normal cool.