Lasse Östman, Swedish potter. More about Crystal Glazes
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!
|I think I have tested
about 2000 crystal glazes today. I use about 50 of them
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,
All, except a few, crystal glazes fire at 1250-1280oC. 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
|Here I will concentrate on 4 of my base
They represent about 80% of my commonly used ones.
|Base Crystal Glaze No 6, silky mat|
|Base Crystal Glaze No 7, glossy|
|Base Crystal Glaze No 6713, glossy|
|Base Crystal Glaze No C4, semi glossy|
Base Crystal Glaze No 6
with ferric and uranium oxide and
a small amount of cobalt oxide.
|This is a very simple glaze, only three
ingredients. Easy to use and not at all difficult. It was
one of my very first crystal glazes, but I use it still
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.............
Base Crystal Glaze No 7
with rutile and ferric oxide.
I have no really good picture.
|Sometimes it gives good crystals, sometimes
not. It gives very sharp colors, flashing orange and
blue. It is one of my earlier glazes. I use it very
Because of its ingredients it is quite unstable and will flow a lot unless not exactly the right thickness and temperature. It was a starting point for further tests that led to one of my best base crystal glazes, the 6713.
Base Crystal Glaze No 6713
with copper, ferric and manganese
with cobalt and ferric oxide
with rutile and cobalt, copper and
|This is one of two favorite bases. I have it
in at least 100 variations. Always good crystals and not
too difficult to master. Crystals up to 1", maybe
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.
Base Crystal Glaze No C4
with cobalt oxide and rutile
Zinc Barium Frit 90420
Rutile or Titanium oxide
|The previous 3 glaze bases are not
containing Frits. This one is based on Borax and Zinc
Barium Frits. I have tested a lot of other Frits too,
Alkaline and Lithium ones. Many are very good. Try it
with your Frits and correct it with the China Clay and
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.
last: Remember one thing - without a good body, the form,
an interesting glaze canīt make a good pot. Crystal glazes needs simple
forms with sparse or no decoration. Else it will be "too much".
luck with your testing of one of the most exciting glaze types!
Donīt use crystal glazes for food ware and be aware of the toxic risks
with some of the ingredients. Have fun!
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