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Crystal glazes are very special glazes. Delicate, strong colors, spectacular crystals of different shapes, and other interesting effects.

They are a bit difficult to master, runny, difficult to repeat exactly. They try your patience. They ruin your kiln shelves. They demand great care and cleanliness. They are expensive and often poisonous to handle. They drive you crazy.

I love Crystal Glazes!

When I have invented a good base crystal glaze, I try to vary the coloring oxides and carbonates. In that way I can get many quite different glazes in an easy way. Sometimes the coloring oxides affects the glaze in a bad manner and I have to correct the base glaze. Be patient - donīt give up!

For further tests I change the Feldspars, try different amounts of Zinc, Dolomite, Rutile, Whiting and Barium (maybe Strontium), change the frits and substitute Lithium carbonate and common Feldspars for Petalite or Spodumene.

For coloring I use: Ferric oxide, Copper oxide and carbonate, Cobalt oxide and carbonate, Nickel oxide and carbonate, Manganese carbonate, Uranium dioxide,
and sometimes: Vanadium pentoxide, Molybdenum oxide, Antimony oxide, Rutile and Ilmenite.

All, except a few, crystal glazes fire at 1250-1280^oC. You can try Orton cone 7-9.

For my normal firing schedule (even crystal glazes!), look at my "Firing Page".

Best is porcelain and white or light gray stoneware clays. Oxidation in an electric kiln. Later I will add recipes for a silky mat crystal glaze that fires in reduction.

I seldom try to get very big crystals. I think the smaller (2-25mm) ones, often very complex, together with running streaks suite my taste better.
I do not use a longer cooling and I do not use other, not so runny, glazes near the bottom.
I spray all glazes in a normal way, and I have not to grind away glaze from the bottom.
But I make a lot of glaze testing and control thickness and temperature very careful. And if you are observant you can see that there is not so little Alumina in the crystal glazes!
Of course you can get very big crystals with my lithium glazes, but then you must apply it and fire it in a little different way (controlled cooling).

with ferric, copper and cobalt oxide.

You canīt expect too large crystals. They are round shaped and the difference between the bottom color and the crystals can be very striking. It will give very good streaks on vertical surfaces. Up to 1" crystals.

It is a very good glaze for use with many coloring oxides. The surface is silky mat to semi shiny. Test it substituting the LR feldspar for your ordinary and change the relations between Zinc oxide and Dolomite. Try to put in Rutile, Barium carbonate and Whiting.............

I have no really good picture.

It was developed from a mix of bases No 6 and 7, about 1/4 of No 6 and 3/4 of No 7. It is much more stable than No 7, and gives good crystals easier than No 6.

I use it with a number of coloring oxides, often 3 to 5 together. In that way I can have both Primary and Secondary crystals of different shape and color on the same piece. Very distinct colors.

It can be sprayed on right to the foot ring, but a little thinner of course.

I have made variations with other Feldspars, have substituted Barium for Strontium or Calcium. A small amount of Rutile is often good. For other temperatures correct the glaze with the Quarts and Lithium.

It is a good glaze to combine with the next, No C4.

This type is as easy to use as No 6713. It often gives 2 or 3 sorts of crystals in the same glaze. Smaller and bigger ones. It is not so shiny as No 6713.

Good with many oxides and carbonates. In some color combinations you must decrease the Rutile.

If you refire it, the crystals may be smaller but more numerous. Test it together with No 6713. Very fascinating results may occur.