creative creek artisans
Home
Where Creativity Flows  
Cone 6 Crystalline Glazes  

Crystalline Glaze for Cone 6

Crystalline glazes are at once fascinating and frustrating. Successful crystalline glazes are the result of using a clay body with no grog or sand (ideally porcelain), manufacture of forms with proper support for the glaze firing, accurate glaze formulation and application and matching a firing schedule to the glazes (perhaps the most critical factor).

 

Crystalline glazes are divided into two basic categories: micro crystalline and macro crystalline. Mat glazes are types of micro crystalline glazes. The surface is created by numerous crystals (too small to be seen by the naked eye) suspended in the glaze matrix. The masses of crystals refract light in such a way as to create a non-shiny surface. Other micro crystalline glazes are referred to as aventurine. The crystals in these glazes are very small, suspended in the glaze, reflecting light like little flitters. Iron and/or titanium are used most often to create this effect.

 

Macro crystalline glazes can be large and spectacular. Crystal shapes such as fans, circles, rods and stars may appear in various sizes seeming to float in a smooth background. The crystals are formed from a combination of zinc and silica, known as zinc orthosilicate, similar to the naturally occurring mineral willemite. Titanium is also used to form crystals to a lesser extent.

 

Normally the ratio of silica (glassformer), flux (melter) and alumina (stabilizer) is established to form a glaze that will remain stable (non-flowing) on a vertical surface at a given temperature. Crystalline glazes differ in the ratio of silica and flux to the amount of alumina. The amount of alumina is small, often, none at all, resulting in a glaze which is very fluid when fired to its maturing temperature. A fluid glaze is necessary to form crystals. The glaze is saturated with silica (positive ion) and zinc (negative ion). During the melting process the positive and negative ions are attracted and bond to each other. As the glaze continues to flow molecules are attracted and bond to form the zinc orthosilicate crystals.

 

There are numerous variables that might affect the formation of crystals in a glaze. Contributing factors, singularly or in combination, may include: thickness of glaze application, firing time, shape of the pot, maximum firing temperature, soaking temperature and soaking time.

 

Factors in Crystal Development

  1. Glaze must be fluid to form crystals.
  2. Glaze coating needs to be thicker than usual.
  3. Glaze is best sprayed or brushed on, but can be dipped/poured.
  4. Glaze which is fresh, well mixed and screened works best.
  5. A fast firing and long soaking (1/2 to 4 hours) time produces more crystal growth.
  6. Fritting of compounds or use of frits, rather than raw materials, is recommended. Most frequently used frits are Ferro #3110 & #3134.
  7. High soda content is better than potash or calcium.
  8. Manganese or iron, under 2%, promote larger crystals.
  9. Zinc should range 10 – 35%.
  10. Titanium contributes to smaller, but evenly distributed crystals. No more than 10%.
  11. Alumina must be less than 10%.

Materials most commonly used in crystalline glazes

  • Silica - 325 mesh: up to 25%
  • Zinc oxide – calcined: up to 35%
  • Frits – sodium, Ferro frit 3110 or GF 134: 50 – 55%
  • Alumina - alumina oxide or hydrate, calcined kaolin - .75 - 2 parts
  • Titanium dioxide/ Rutile – 1 - 6%
  • Tungsten - crystal enhancer, .5 -.75 parts
  • Vanadium Pentoxide - crystal enhancer, .1 -.5 parts
  • Molybdic oxide - crystal enhancer

Coloring Oxides in Crystal Glazes

 

Cobalt: Almost always blue on a lighter blue background. Use .2 – 3%. Addition of zirconium and/or tin will lighten and opacify. Works well with copper and manganese.

 

Copper: Various greens on green background. Green on cream background and turquoise blue also occur. Use 1-3%. Combinations with cobalt, nickel and manganese.

 

Nickel: May produce silver on brown, blue on amber or blue-green on chartreuse. Use 1-3%. Use with copper and cobalt. Do not use with titanium.

 

Manganese: Results may yield lavender/pink on tan, silver on tan, orange, brown or purple/brown. Use .5-4%. Works with cobalt and copper.


Iron: Gold on brown, gold/brown on orange and various tan/brown combinations. Use 2-5%.

 

Rutile: Golden brown on brown to tan background. Is an impure form of titanium; do not use too much. Works as a modifier of other colors.

 

Illmenite: May create blues on tan/brown. Use .5-2%.

 

Tungsten: Can produce a luster surface. Reacts similar to titanium as a crystal enhancer. Do not use very much. Use .5-2%

 

Combinations of oxides will produce any number of results. Factors include: specific oxides, percentage of oxides and the base glaze formula. One should expect to see changes in color of the crystals, the color of the background and the shape and size of the crystals. Colorants may also affect the glaze melt. Most colorants act as fluxes, except nickel, which acts as a refractory.

Helen's Crystal (Snair)

Frit GF 134 (FF3110) – 48.48
Zinc Oxide – 24.35
Calcined Kaolin – 1.52
Silica – 17.95
Lihium Carbonate – 5

MFE Crystal (Turnidge)

GF 134 – 50
Zinc – 22.5
Silica – 22.5
Lithium Carb - 2 - 5

Fa’s Tin Foil

GF 134 – 50
Zinc – 25
Silica – 18
Whiting – 5
Tin Oxide – 2
Optional - Lithium Carb – 5

Fa’s Octal

GF 134 – 51
Zinc – 24
Silica – 15.4
Dolomite – 4.8
Titanium Dioxide – 2.9
Spodumene – 1.9

Fa’s Cone 6 Base rev

GF 134 – 53
Zinc – 27
Silica – 15
Titanium – 3
Dolomite – 2
Lithium Carb – 5

Untitled

Frit 3110 - 28
GF 106 - 25
Zinc - 24
Silica – 13
Titanium Diox - 2
Lihium Carbonate – 5

Bory #1 rev

Frit 3110 - 50
Zinc - 27
Silica - 16
Lithium Carb - 2
Titanium Diox - 2
Gerstley Borate - 1

Untitled

Frit 3110 - 55
Zinc - 30
Silica - 15
Gerstley Borate – 2
Lithium Carbonate - 2
Titanium Diox - 1

Manual Firing Schedule

(Manual Kiln, L&L, J18X, 3 sections, infinite switch for each section.)
• Kiln on high
• ^6 over in 4 1/2 hours
• Kiln off, drop to 1000 – 1040°C
(1835 – 1905°F) about 30 – 45 minutes
• Kiln on, switches vary between “L” – “2”
• Hold temperature 4 hours

Programmable Controller Firing Schedule

(L&L J18X-3, Dynatrol Controller)
• USEr/1
• SEG/2
• rA1/500
• °F1/2230
• HLd1/.05
• rA2/500
• °F2/1800
• HLd2/4.00

 

USEr/1 - Firing profile, SEG/2 - two segments, rA1/500 - heating rate per hour, °F1/2230 - firing temp,


HLd1/.05 - 5 minute hold at temp, rA2/500 - drop to cooling temp, °F2/1800 - holding temp,


HLd2/4.00 - hold time 4 hours


Total firing time 10- 101/2 hours

 

Some recent results suggest a higher holding temperature may produce larger crystals.

 

Crystalline Glaze Bibliography

Texts

Glazes For Special Effects by Herbert Sanders,  Watson-Guptill Pub. 1974

 

Contemporary Ceramic Formulas by John W. Conrad,  MacMillen Pub. Inc.  1980

Crystalline Glaze Text by Dan Turnridge,  Turnridege Porcelain  1990

 

Crystalline Glazes by Diane Creber,  University of Pennsylvania Press  2nd Ed. 2005

Includes a section on my work with crystalline glazes for cone 6.

 

Macro-Crystalline Glazes The Challenge of Crystals by Peter Ilsley,

The Crowood Press  1999

 

Crystal Glazes by Fara Shimbo, Digitalfire Corp. http://digitalfire.com/books/518.php  2001 – An E-book on crystalline glazes, 2nd revised edition.

Fara Shimbo’s web site: http://crystalline-ceramics.info

 

The Art of Crystalline Glazing, Basic Techniques by Jon & LeRoy Price, Krause Pub., 2003 

 

Articles

Making and Firing Crystalline Glazes by David Snair, Ceramics Monthly, Dec. 1975

 

Crystal Glazes in Reduction by Thomas S. Carroll, Ceramics Monthly, Mar. 1991

 

Crystalline Glazes: A Precise Method by Bevan Norkin, Ceramics Monthly, Mar. 1992

 

Crystalline Glazes, a series of articles, The Studio Potter, Vol. 25, No. 1, Dec. 1996

 

Crystalline Alchemy by Kate Malone, Ceramic Review 164 - 1997

 

Crystal Glazing by Annet Hamster, Ceramic Review 174 – Nov/Dec. 1998

 

Cone 6 Crystalline Glazing by William Schran, ClayTimes, Sept/Oct. 2000

WEB SITES

 

http://home.swipnet.se/isaksson./glasbasEng.htm – list of various crystalline glazes
http://www.barra.se/stoneware/glasyrer/crystal.htm – Swedish potter, list of glazes
http://its2.ocs.lsu.edu/guests/wwwlawl/lawctr/ccreference.htm#techniques – reference list
http://www.dawnmist.demon.co.uk/xtlsupp.htm - English supplier of commercial crystal glazes
http://www.krceramics.com/english_index.htm - Chinese crystalline glaze potter
http://www.chinaimporters.com/vase/cover2.htm - Chinese crystalline glaze pottery exports
http://home.tiscalinet.ch/magyk/index.html - Magy Reist, crystal glaze potter
http://www.jonpriceceramics.com/ - Jon Price, crystal glaze potter
http://www.seagrovepotteries.com/phil_morgan_pottery.htm - Phil Morgan, crystal glaze potter
http://www.johnstroomer.com.au/home.html - John Stroomer, crystal glaze potter
http://www.wlotus.com/RichardKlump/default.htm - Richard Klump, crystal glaze potter
http://faculty.law.lsu.edu/ccorcos/lawctr/cchistory.htm - crystal glaze links
http://www.palacenet.net/home/jrein/artwork.html - Jerry Reinwand, crystal glaze potter
http://crystalline-ceramics.info - Fara Shimbo, crystal glaze potter
http://www.ceramicstoday.com/ - ceramics list & web links
http://home.earthlink.net/~bsondahl/cryscolor.html - crystalline glaze color tests
http://www.milkywayceramics.com/mf/glazes.htm - crystal glaze, getting started
http://www.milkywayceramics.com/mf/literature.htm - crystal glaze literature/articles
http://board3.cgiworld.dreamwiz.com/list.cgi?id=Crystal - Crystalline Glaze Forum started and moderated by William Melstrom. Post questions and images, get information from some of the experts in the field.