Cone 6 Ravenscrag Slip Glazes

Every potter wants a good reliable glossy black glaze that has a minimum of toxic metals and fires to an even color without pinholes and blisters. Ravenscrag slip has the unusual ability to host a black color from a high iron content (only a tiny amount of cobalt oxide and chrome oxide are needed).

-This recipe is a clear even glossy glaze with a smooth surface. Passes the hot/cold crazing test on M340.

Suggested additions:
- 5% titanium dioxide, 1% cobalt oxide, 1% copper oxide and 0.5% iron oxide for a light glossy blue glaze with some lighter variegations, breaks to a green over the edges.
-3% Cobalt Carbonate, 3% Rutile, 3% Titanium for a variegated light medium blue glaze that breaks greenish over edges.
-2% copper oxide and 2.5% titanium dioxide (survives vinegar test without leaching). Produces a celadon green with some crystal growth on the bottom of the bowls where it pools if thick or if cooled slowly.
-12% zircopax for a white Majolica type glaze
-12% iron oxide red, 1.5% cobalt oxide for a dark black with a tinge of blue.
- 2% Chrome Oxide, 2% Cobalt oxide for a dark teal.

Liner glaze: Add 0.25-0.5% Mason 6300 blue to get a brighter effect on stoneware bodies that might otherwise appear straw yellow under the glaze.

David Shaners cone 6 floating blue has been used for many years by thousands of potters. However it contains gerstley borate which is no longer available (see GerstleyBorate.com for information in this classic recipe and the material). In addition it is a temperamental recipe and is prone to blistering. This version is much more reliable and has all the other benefits afforded by a high Ravenscrag content.

Application should be thin to medium and a fast cool down is required to prevent crystallization. It can be fired to cone 5 or 6.

This is a high alumina matte glaze and is a favorite. It is not temperature sensitive and produces good results at cone 5, 6 and 7 (medium blue surface breaking an olive type green where thin). Most base glazes do not host alumina well and fire with pitting and uneven surface (alumina is very difficult to melt and dissolve). Be sure to use a smallest particle sized alumina you can find (it is available in very fine grades, much finer that the average ceramic material).

Note: We are recommending GA6-B Alberta Slip oatmeal glaze instead, it looks better and has a better melt. Alberta Slip is already a stained material, so less colorants are needed to make darker colored glazes. Go the http://albertaslip.com.

Good oatmeal glazes can be difficult to achieve at cone 6 oxidation. Application should be thin to medium.

This type of glaze is very difficult to achieve at cone 6 since the chrome and tin require high calcium, zero zinc and low boron. Bases that work fine with other colors will often produce grey with chrome-tin pink or maroon stains or oxide combinations. Glazes that do work in this system are normally highly fritted so the chemistry is sympathetic to the color development, however such glazes are often difficult to work with. This base is the opposite, it has beautiful working properties, you can do multiple layers and it has all the other benefits imparted by a high Ravenscrag Slip content.

Medium to medium thick application is best. Breaks clear around edges to highlight irregularities in the surface.

This produces a variegated light medium blue glaze that breaks greenish over edges. This glaze is very consistent and has very good working properties.

Variations

5% titanium dioxide, 1% cobalt oxide, 1% copper oxide and 0.5% iron oxide: A light glossy blue glaze with some lighter variegations, breaks to a green over the edges.

3% Cobalt Carbonate, 3% Rutile, 3% Titanium dioxide: A variegated light medium blue glaze that breaks greenish over edges.

2% copper oxide and 2.5% titanium dioxide: Does not leach on vinegar test. Produces a celadon green with some crystals growing on the bottom of the bowl where it pools. Normal application

A white base glaze with all the advantages of Ravenscrag Slip based glazes (not highly fritted, you can do multi-layering, it is not drab look like a porcelain sink or toilet).