Zinc Ortho-Silicate Crystal Glazes

Crystal Glazes & Recipes

True Cone 10 Zinc Crystal glazes have fascinated potters for the last hundred years. One major advance, digital controllers, put Crystal glazes in reach of any potter. In this short article, I will outline the basics and give some recipes.

Clay: use a smooth, white clay for cone 10; such as New Mexico Clay' s Domestic, CK-mix, or any cone 10 porcelain. Try making plates or tiles at first, as crystal glazes are VERY runny*. If you wish to make a vase you must throw a little dish to fire your pot on; after bisquing, glue the dish and the vase together with alumina hydrate.

The glaze: After trying many different glazes, I recommend one based on Ferro Frit 3110. Herbert Sanders book on Glazes for Special Effects (sadly, out of print) lists this as Glaze #3. 

 
  • FF3110--- ---------------------52%   
  • Calcined Zinc Oxide------------24%
  • Silica 325 mesh-----------------24%
  • To this base glaze add:
  • Rutile ----------------- 2%
  • Bentonite------------- .75%
  • Epsom salts--------- .3%
  • CMC------------------- .5%

Notice that this glaze is very high in Zinc and contains no Alumina. The excessive amount of Zinc crystallizes into Zinc Orthosilicate crystals in the glaze, the same way sugar when super saturated in water will turn into rock candy. Low alumina allows the necessary fluidity* that the crystals need to be able to grow.



For color add these oxides to base glaze:

Cobalt Carbonate .75% to 1% for dark blue crystals with a lighter background.

Iron Oxide 4% for brown crystals.

Nickel Oxide Green 4% for blue green crystals on brown background.

Manganese Dioxide 1% to 4% for lavender on tan.

Uranium Oxide 6% to 10% for yellows and golds.

Praseodymium Oxide for white with yellow edges.

Apply the glaze by spraying onto bisque, as it contains no clay and is horrible to brush on. Try layering the glazes, as opposed to mixing the oxides, for interesting varied colors.

Firing: In general fire to cone 10, cool the kiln to 2000 degrees and hold for 3 to 5 hours in-between 2000 and 1800 degrees. 

With a digital kiln a firing would go like this:


Ramp 1: rate 250°, to 1000° no hold.

Ramp 2: rate 500°, to 2320° hold 15 minutes. (00.15)

Ramp 3: rate 500° (to 9999 to cool faster), to 2000° hold for 03.00 hours.

Ramp 4: rate 500°, to 1800° hold for 01.00 hours.

Let cool, no peeking!

Brant Palley


*These glazes are very runny. A catch plate is a base you throw that matches the bottom of the pot, it is then glued onto the bottom of the pot with a mixture of alumina hydrate and elmers glue. After firing the catch plate is removed and the bottom is ground to a nice finish. That is why I just made plates and bowls, not vases.

The Sandia Mountains - Plate by Brant Palley Cone 10 crystal glazes 1988

Zinc Ortho-Silicate Crystal Glazes

Low-Fire Casting Slip, White in 1 Gallon Jar

$10.46 Per Gallon in wide mouth Jar
  • Obsidian Clay ^5/6

    $1.60

    Aardvark Clay's Obsidian Cone 5

    Very black, ebony like finish. Needs lots of oxygen during bisque firing.

     

     (Formerly Cassius Basaltic) Fired Shrinkage is 14.5% and Water Absorption is .5% when fired to cone 5.


  • Giffin Grip Mini

    $199.00

    Giffin Grip Mini

    The Giffin Grip Mini is a re-centering tool for potters. 

    Designed specifically for trimming, it works equally well for waxing the foot or banding.
    After a simple one time adjustment, the Giffin Grip quickly snaps on and off  your wheel.

    Features

    • Centers and holds your pots with ease
    • Fits all standard wheel sizes, Does fit the new Shimpo Aspire™
    • Is assembled
    • Ergonomically shaped hands gently hold your pot in place
    • Works for many functions in addition to trimming, including waxing the foot & banding with oxides

    Box Includes:

    • lengths of rods with hands
    • Sliders
    • Sliders

    works both ways


  • IRONSTONE

    $0.90 Per Pound As low as: $0.59 Per Pound

    IRONSTONE  Black Clay Cone 6

    NEW and Improved black clay, fired to cone 6

    Has a lot of iron in the body, a magnet will actually stick to it!

    A medium texture clay body, will not stain your hands. Glazes react to the high iron content, and may speckle.

    This clay has a wide reaction to temperature, glazes, and atmosphere, you should do a lot of testing. 

    Please post your results to #ironstoneclay and #blackclay.

  • StudioPro SpaceSaver Bat System

    $60.00

    StudioPro SpaceSaver Bat System

    The SpaceSaver is a convenient system for making smaller pots and maximizing table space in your studio. The entire system is fully compatible with the now unavailable Wonderbat. It consists of a 14" adapter bat and 8- 6" insert bats. Both are made from a 1/2" exterior grade MDF which provides excellent bottom drying and rigidity. The adapter bat mounts on standard wheel-head pins with rubber "through hole" grommets making a true two-sided bat.