technique - crystalline glaze

Crystalline Glaze

Crystalline glazes instantly capture the eye. They can dazzle and excite. They are seductive. Turning a piece to the light, the intricate crystals appear to float within the glaze. Images of frost, flowers or thistles blowing In the wind excite the imagination. Using crystalline glazes is much more than a technical process involving recipes and firing schedules. It is understanding what crystals are, how they grow, the ingredients that go into a crystalline glaze and how each ingredient reacts in the melt. To really know the glaze and when to use it is a skill that requires research, time and sensitivity to artistic expression. History The process has existed for over 1000 years. Some say crystalline glazes were first made in the Orient many centuries ago. Ancient Chinese oil-spot glazes from the Sung Dynasty (AD 960-1279) contain very small crystals, but they may have been unintentional. Perhaps the potter was trying to prolong the cooling of the kiln and the crystals developed accidentally. The history of crystalline glazing as we know it began in the 19th century. It was not until the development of the Art Noveau movement that crystalline glazes became popular. Among the first scientists working on ceramics was Alexander Brongniart at the Sevres National Porcelain Factory in France. He produced some crystalline glazes around 1850. However, the Sevres factory did not start formally producing crystalline glazes until 1897. In Berlin Wilhelm Pukall, a chemist from the Royal Porcelain Manufactory, who was also head of the Royal Ceramic College, worked with crystalline glazes and published his results in 1908. In England Royal Doulton became internationally recognized for their outstanding achievements with crystalline glazes. At the Brussels Exhibition in 1920, every piece was sold within hours of the opening. Doulton stopped producing crystalline glazes because they were very expensive and the technique too unpredictable. The idea of artist-potter changed dramatically during the 1920s and 1930s. Individual potters now performed nearly all the production processes. The factories could mass-produce the functional ware; folk art could no longer compete, but artist-craftsperson became a means of defense against the materialism of industry and its insensibility to beauty. Studio potters have been working with crystalline glazes for about the last 50 years, some obtaining remarkable results. Most find their own unique way of working with crystals and have developed their own glazes and firing procedures, the methods being as varied as the crystals themselves.

Technique

Crystalline glazes are those special ceramic glazes in which crystals actually grow inside the glaze while it is still very hot (about 2100 F). The crystals start out as microscopic spots in the glaze, called "seeds." These seeds form spontaneously in the glaze, in random numbers and locations. The glaze is first fired to about 2500 F. to thoroughly melt all of the ingredients. It is then cooled to the crystal-growing temperature, where the crystals start growing on the seeds. The longer the glaze is held at that temperature (from 6 to 12 hours), the larger the crystals get-- until the maximum size for that particular glaze is attained. In order for the crystals to grow, the glaze must be very fluid. Because of this, much of the glaze runs off the piece during the firing. In order to contain the run-off, a catch basin and specially-shaped pedestal are made for each piece. The piece is placed on the pedestal in the catch basin for the firing. After the firing, the piece is carefully separated from the pedestal, and its bottom is ground flat. Most potters consider crystalline glazes to be the most difficult and challenging of all glazes to produce. This is because they are unusually difficult and time-consuming to formulate and fire. They require meticulous attention to every detail. Also, the "success rate" is much lower for this glaze than for any other. Usually less than 50% of the pieces turn out; the others either have poor color, no crystals, or break.


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									Crystalline Glaze Crystalline glazes instantly capture the eye. They can dazzle and excite. They are seductive. Turning a piece to the light, the intricate crystals appear to float within the glaze. Images of frost, flowers or thistles blowing In the wind excite the imagination. Using crystalline glazes is much more than a technical process involving recipes and firing schedules. It is understanding what crystals are, how they grow, the ingredients that go into a crystalline glaze and how each ingredient reacts in the melt. To really know the glaze and when to use it is a skill that requires research, time and sensitivity to artistic expression. History The process has existed for over 1000 years. Some say crystalline glazes were first made in the Orient many centuries ago. Ancient Chinese oil-spot glazes from the Sung Dynasty (AD 960-1279) contain very small crystals, but they may have been unintentional. Perhaps the potter was trying to prolong the cooling of the kiln and the crystals developed accidentally. The history of crystalline glazing as we know it began in the 19th century. It was not until the development of the Art Noveau movement that crystalline glazes became popular. Among the first scientists working on ceramics was Alexander Brongniart at the Sevres National Porcelain Factory in France. He produced some crystalline glazes around 1850. However, the Sevres factory did not start formally producing crystalline glazes until 1897. In Berlin Wilhelm Pukall, a chemist from the Royal Porcelain Manufactory, who was also head of the Royal Ceramic College, worked with crystalline glazes and published his results in 1908. In England Royal Doulton became internationally recognized for their outstanding achievements with crystalline glazes. At the Brussels Exhibition in 1920, every piece was sold within hours of the opening. Doulton stopped producing crystalline glazes because they were very expensive and the technique too unpredictable. The idea of artist-potter changed dramatically during the 1920s and 1930s. Individual potters now performed nearly all the production processes. The factories could mass-produce the functional ware; folk art could no longer compete, but artist-craftsperson became a means of defense against the materialism of industry and its insensibility to beauty. Studio potters have been working with crystalline glazes for about the last 50 years, some obtaining remarkable results. Most find their own unique way of working with crystals and have developed their own glazes and firing procedures, the methods being as varied as the crystals themselves. Technique Crystalline glazes are those special ceramic glazes in which crystals actually grow inside the glaze while it is still very hot (about 2100 F). The crystals start out as microscopic spots in the glaze, called "seeds." These seeds form spontaneously in the glaze, in random numbers and locations. The glaze is first fired to about 2500 F. to thoroughly melt all of the ingredients. It is then cooled to the crystal-growing temperature, where the crystals start growing on the seeds. The longer the glaze is held at that temperature (from 6 to 12 hours), the larger the crystals get-- until the maximum size for that particular glaze is attained. In order for the crystals to grow, the glaze must be very fluid. Because of this, much of the glaze runs off the piece during the firing. In order to contain the run-off, a catch basin and specially-shaped pedestal are made for each piece. The piece is placed on the pedestal in the catch basin for the firing. After the firing, the piece is carefully separated from the pedestal, and its bottom is ground flat. Most potters consider crystalline glazes to be the most difficult and challenging of all glazes to produce. This is because they are unusually difficult and time-consuming to formulate and fire. They require meticulous attention to every detail. Also, the "success rate" is much lower for this glaze than for any other. Usually less than 50% of the pieces turn out; the others either have poor color, no crystals, or break.