A Passion for Ceramics
here a very nice and comprehensive report on how to make crystals... by my friend Ian Childers...
Crystalline by nature is comparatively expensive to produce. It is labour intensive, demands meticulous record keeping and exacting control of all materials and processes. It is one of the more challenging techniques a potter can undertake. Losses can be dramatic and heartbreaking and for this reason Crystalline is considered by most potters too difficult to undertake or pursue to any degree.
White porcelain clay is generally the material of choice for throwing as any impurities in the clay will affect the colour and growth of the crystals. Due to its lack of body and ability to stand up on the potter's wheel the use of porcelain clay demands skill, especially on large pieces.
The specially formulated crystalline glazes require careful application and are fired up to peak temperatures of 1320 Celsius
(2400F) over 18 hours. At these temperatures the glaze is very fluid and has the tendency to flow from the surface of the pot.
This fluidity necessitates the pot being attached to an added pedestal and catch basin to contain any glaze runoff.
The glaze runoff during firing requires the pot to be separated from the base after firing. The separation process of cutting, grinding and polishing can cause substantial losses, especially of larger pieces which can often crack due to the tension created on cooling between the pot and its pedestal.
Once peak temperature has been reached, the kilns are rapidly cooled to pre-determined temperatures where the crystals are grown. As crystal formation requires slow cooling, these temperatures are held and further manipulated within this growth window for a further 6-12 hours or more to allow for crystal growth within the glaze matrix.
Crystals are formed at random, can take on a myriad of shapes and are three dimensional in nature. In direct sunlight or strong light, spectacular effects created by the refraction of light bouncing off the crystals give each piece a three dimensional quality and depth. Crystalline is one of the most stunning glazing techniques available.
Metallic oxides and combinations of various materials are used to produce a wide range of colours. These range from dark cobalt blues through to golds, browns, pinks, pearls and reef greens.
The beauty, depth and life expressed in a Crystalline glaze is spectacular and unsurpassed. It is a challenge to even the most experienced and knowledgeable potter. Like the gems which come from beneath the earth's surface, the Crystalline process does not come easily and must be won by many hours of hard work and dedication.