Glaze recipes

A glaze that gives a good soft blue with a textured surface at cone 9, becoming smooth an glossy at cone 10 and above is:

Potassium feldspar 38.1, Whiting 20.2, Talc 3.8, China clay 19.0, Flint 28.9, Iron oxide 0.5 - 0.7

Green celadon

Take any glaze from the biaxial, or the above glaze, and add 0.2% titanium dioxide to turn the pale blue to a green. Alternatively recalculate the glaze with HVAR (or another) ball clay rather than the pure china clay. If the iron oxide content is increased above 1% the colour of the glaze will deepen and become increasingly green. Try a line blend from 1 to 3% iron oxide in half percent incements. With iron at 3% and above glazes tend to be increasingly 'dirty' green and olive in colour. Fluid glazes are often gorgeously bright emerald where thick but tending to brown where thin.

Again, a glaze can be taken from the previous triaxial and the iron oxide ommited. From the biaxial it can be seen that increasing alumina and silica in a glaze decreases crazing. The glazes therefore tend to get stiffer and less interesting, so it can be useful to add some borax frit to improve the glaze.Certain fluxes also promote craze free glazes - most useful are magnesium and lithium. A glaze can be reworked substituting magnesium (eg as talc) or lithium (eg. in petalite) for some of the potassium (feldspar) using the Seger formula for the glaze.

A couple of glazes that I developed that have proved quite useful are:

1. Potassium feldspar 28.3, whiting 19.1, china clay 17.4, flint 35.1, talc 4, borax frit 5. Which can be reworked substituting in some lithium to reduce crazing further to: Potassium feldspar 14.3, petalite 19.1, whiting 19.4, china clay 16.5, flint 30.8. The petalite reduces the maturation temperature of the glaze so the borax frit will probably be unneccessary.

2. Potassium feldspar 28, whiting 15.2, talc 6.8, china clay 20, flint 30, borax frit 5.

It is much easier to get glaze fit on some clay bodies than others eg. Southern Ice Porcelain and Valentines Special porcelain. It is by no means essential to have an uncrazed glaze on a stoneware body, but it is important to note that a pot with an uncrazed glaze is about 4 times stronger than one with a crazed glaze. Also the craze lines tend to get stained with use, which can make eating beetroot soup a less pleasurable experience.

A high iron glaze. An iron content of 8% in reduction is probably OK in reduction, but 10 or 11% will be needed on porcelain or in oxidation to give a dense black with good rust break on edges.

Examples are:

Potassium feldspar 72.1, Whiting 10.4, flint 15.6, red iron oxide 8 - 11, bentonite 3 - a glossy black tenmoku.

Potassium feldspar 42, whiting 18.5, china clay 11.2, flint 27, rediron oxide 8 - 11.

Again you could take the previous biaxial and add 8 or 10% red iron oxide to each glaze for an interesting set of results. Iron oxide is a flux, especially in reduction, so all glazes will be more fluid and glossy. Any crystals remaining in the glaze (esp. if only fired to cone 9) will be gold in colour. This effect can be increased by adding more talc in a simple lineblend.

These glazes are produced by an overload of magnesium in the glaze, whic crystallizes out on cooling producing opacity and a varity of satin to matt surfaces. Increasing the magnesia (or reducing silica and alumina) tends to increase the mattness of the glaze surface. As a result of this these glazes tend to craze, which can cause problems on porcelain - beautiful kiln loads of pots cracking apart as they see the light of day. Crazing can be eliminated on some bodies using flux substitution, though this isn't generally a problem on stoneware.

A good starting point is: Potassium feldspar 40, whiting 16, talc 11, china clay 7, flint 26. OR Nepheline syenite 20, whiting 15, talc 15, china clay 16, flint 28.

It is important to note that as these are high flux (magnesium) glazes, they are satin and static at cone 9 but will become increasingly fluid at the temperature is increased, eventually becoming very runny clear glazes!

Copper red: Potassium feldspar 79, borax frit 9, whiting 12, bentonite 3, copper carb 1, tin oxide 1.

Reduction honey: Potassium feldspar 54.8, whiting 23, flint 18.5, bentonite 3, red iron oxide 8.

Calcium matt: Potassium feldpar 60, whiting 20, china clay 20. Good base for colour additions.

Another: Potassium feldspar 35, china clay 30, whiting 30, dolomite 5, bone ash 5. A good base for colour additions - copper gives a lovely soft aqua at 1% in oxidation, darker with charcoal crystals at 3%.

Peach bloom red: Nepheline syenite 25, whiting 15, flint 20, china clay 15, alkaline frit 20, borax frit 5, tin oxide 3, copper carbonate 1.

Deep blue cone 8-9: Potassium feldspar 42.2, whiting 19.5, flint 13, china clay 15, borax frit 11, red iron oxide 2, cobalt carbonate 2.

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At present this section is rather small. After many months of tests on various new materials I managed to reconstruct my Australian glazes, but have not managed to recreate effects I was managing to acheive in my salt kiln in Australia. Partly this is due to the very different nature of the clays in the two countries, also because I was using a lovely impure clay I dug from a friends property as one ingredient in nearly all my slips and clay bodies. Commercial clays don't seem to give as interesting results.

The recipes I have to share so far are:

Light tan/yellow: HV clay 50, china clay 50.

Pink: Grolleg china clay 85, porcelain powder 15.

Dark tan: AT ball clay 60, china clay 40, red iron oxide 1.

Red/tan/yellow (depending on amount of salt) slip: AT 45, china clay 45, nepheline syenite 20.

Brown: ESVA 50, china clay 50.

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