Bisque Firing: The Prologue to the Beauty of Porcelain
When we appreciate a Ru porcelain that is as smooth as jade, or a blue and white porcelain that is as transparent as water, we often only pay attention to the lustrous glaze, but few people know that before the glaze, there is an important process that determines the success or failure - bisque firing .
Bisque firing may seem low-key, but it is a key step in the transformation of ceramics from "clay" to "porcelain".
What is bisque?
Bisque firing, as the name suggests, means "firing the base of the porcelain." It refers to the process of pre-firing the porcelain body in a kiln at a temperature of around 800-1000°C before glazing.
During this firing, the body still maintains its plain color without any glaze embellishment, but it has transformed from a fragile "clay embryo" into a tough "semi-finished product", laying the foundation for the next step of glazing and high-temperature firing.
If glaze firing is the "transformation" of porcelain, then bisque firing is the "refining" of porcelain.
Why do elements burn?
In the world of ceramics, bisque firing plays a vital role, just like the "draft" of an article.
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Increased Strength, Reduced Damage <br data-start="465" data-end="468">After drying, the green body is very brittle and can break at the slightest touch. After bisque firing, the body becomes hard and strong enough to withstand glazing, handling, and even re-kilnization.
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Eliminate moisture and impurities <br data-start="540" data-end="543">During the bisque firing process, residual moisture, organic matter, and impurities in the body are completely decomposed and expelled. Without these hidden dangers, the porcelain will not explode due to gas expansion during glaze firing.
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Optimizing the Body Structure <br data-start="623" data-end="626">After bisque firing, a stable microporous structure is formed inside the body. These tiny pores not only ensure the body's air permeability but also facilitate the adhesion of glaze. In other words, bisque firing prepares the body for glazing.
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Reduce deformation and cracking <br data-start="712" data-end="715">Unbisque-fired porcelain bodies are prone to uneven heating during high-temperature glaze firing, resulting in cracking or deformation. Bisque firing, on the other hand, "tames" the body in advance, allowing it to better maintain its original shape during the high fire.
The art of temperature
The temperature selection for biscuit firing is extremely important.
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Too low : The blank is still fragile and has no reinforcement effect.
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Too high : The body is too dense, the water absorption is reduced, and the glaze is not easy to penetrate.
Therefore, craftsmen often control the temperature between 800°C and 1000°C . This range can not only improve the strength of the body but also retain the water absorption rate suitable for glazing.
It can be said that unglazed baking is a "test of just the right amount".
Unglazed and the Beauty of Porcelain
Throughout history, from the blue and white porcelain of Jingdezhen to the masterpieces of famous kilns such as Ru Kiln, Guan Kiln, Ge Kiln, and Ding Kiln, all of them had to undergo bisque firing without exception.
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The cobalt blue color of blue and white porcelain requires a solid "canvas" after bisque firing;
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The warmth and smoothness of the Ru porcelain celadon glaze is inseparable from the firm support of the base.
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The rabbit-hair and Yaobian glazes of Jianzhan can only be stably presented by relying on the body structure after unglazed firing.
Bisque firing is not only a technical process, but also a precipitation of craft aesthetics.
Summarize
The bisque firing process may not be as stunning as the kiln firing, nor as dazzling as the glaze, but it is the "prologue" in the life of porcelain.
Without bisque firing, there would be no tough body; without bisque firing, the brilliant glaze color could not be achieved.
Just like writing an article requires a draft and building a tall building requires a foundation, although bisque firing is "plain", it is an indispensable preparation before porcelain can be transformed into a gorgeous piece.
-Brewin Teaware
