Will adding agate into the glaze have much impact on the properties and color of the porcelain glaze?
The glaze color and quality of genuine Ru porcelain do not depend on whether agate is added to the glaze?
The agate in the glaze is just a pile of materials, and it just reflects the royal luxury?
Chen Wenzhe definitely does not agree with these views, because this is obviously not the case!
First, there is no precedent for agate being glazed, nor has it been done before. There was no such thing in the official kilns of the Northern Song Dynasty, nor the official kilns of the Southern Song Dynasty, nor the official kilns of the Ming and Qing Dynasties.
Since Emperor Huizong of the Song Dynasty could build the "Huashi Gang", why not transport gemstones as raw materials from all over the country to produce "Northern Song Dynasty official kiln" products?
In fact, the agate used in Ru kiln was not the emperor’s favorite; it was an invention of local kiln workers;
Second, the emperors of the Ming and Qing Dynasties cherished your porcelain and imitated it many times. Wouldn’t they use precious stones as glaze?
In fact, both Ming and Qing imitations of Ru porcelain cannot achieve the effect of Song Dynasty Ru porcelain;
The "celestial glaze" porcelain imitated by Ru kiln in the Kangxi period is quite expensive, but it is not fired with iron reduction, but with cobalt as the coloring agent. The effect and difficulty are not as good as the Ru kiln porcelain of the Song Dynasty.
Comparable.
Third, why is only agate used in the glaze and not other gemstones?
There are many quartz gemstones, such as crystal, opal, tiger spar, etc.;
There are many places with gemstones across the country. Why don’t other kilns use gemstones as glazes, but your kiln only uses them?
All kilns use local materials to fire porcelain, which is consistent with objective facts.
The Ru kiln craftsmen's "agate into the glaze" is an innovation. Burning the azure color of Ru porcelain to the extreme is the Ru kiln craftsmen's pursuit of excellence.
It is recorded in "Tanzhai Biheng" by Ye Ji from the Southern Song Dynasty that "the Dingzhou white porcelain had awns and was unusable, so it ordered Ruzhou to make green kiln wares. Therefore, Hebei Tang, Deng, and Yaozhou all had them, and Ru kiln was the leader."
It is authentic and trustworthy.
Ruzhou is a large place with many kiln entrances, but only the Ru kiln in Baofeng Qingliang Temple produces the best.
The value of Ru kiln lies in its shape and glaze color, and there must be a reason why agate is used in the glaze.
The luster of Ru kiln porcelain is very subtle and restrained, as soft as silk and as moist as jade, which is in line with the traditional Chinese concept of modesty and implicitness.
However, it is difficult to achieve a subtle luster on the glaze of porcelain without being dazzling. To achieve this, the glaze needs to be thickened.
This requires adding alkali metals to the calcium glaze to enable thick glaze.
The earlier lime glaze flowed as soon as it was thickened, and it was difficult to achieve a subtle and restrained moistening effect. This was limited by the historical conditions at that time.
Therefore, Ru kiln craftsmen boldly broke through the tradition and invented the agate glaze.
The first time Ru kiln craftsmen added agate, it must have been an unintentional move.
Just like adding malachite to the Jun kiln, it was an unintentional move, and the result was a copper-red glaze.
Agate has a waxy luster, birefringence and high refractive index, which must have a very important impact on the azure color, opacification and jade texture of the glaze.
The discoloration effect of your porcelain glaze under sunlight is also the result of the light reflected by the agate's non-birefringent properties.
The porcelain glazes at other kiln entrances are incomparable.
Ru porcelain uses lime glaze, and the glaze layer is thin. The official kiln and Longquan kiln of the Southern Song Dynasty use lime alkali glaze, which requires multiple glazing to achieve the jade texture.
Seeing this, Chen Wenzhe gained a lot, especially the knowledge about agate glazing.
Furthermore, he discovered that there were two deviations in his cognition. One was that the agate glaze had little to do with the azure color of Ru kiln.
Although he knew that the glaze of agate was related to the glaze color of Ru kiln porcelain, he really didn't expect that the relationship was so big.
Another thing is that Ru kiln porcelain may use lime alkali glaze, so that thick glaze can be applied.
But after seeing the firing process of Ru kiln and the lessons learned by Yan He, he realized that things were not at all what he imagined.
First, the glazing of agate is very important. It is related to the color change of the porcelain, the color shaping, and the texture of the glaze, especially the jade-like texture.
Second, the Ru kiln porcelain used lime glaze instead of lime alkali glaze. However, the craftsmen of Ru kiln also produced thick glaze.
And this thick glaze is different from the thick glaze of lime alkali glaze.
In comparison, Ru kiln glaze is thinner, but its effect is no worse than that of Southern Song Dynasty lime alkali glaze.
And this must be related to the agate glaze. Without the additive of agate, the simple lime glaze will definitely not achieve the effect of Ru kiln porcelain.
These techniques are all real stunts!
If he hadn't seen the firing process of the Ru porcelain in front of him, if he hadn't seen Yan He's works, how could he know these secrets?
There is a certain connection between the azure color of Ru porcelain and the agate glaze. As long as the research is thorough, it will be easy to produce high-quality Ru porcelain.
After reading some secrets, Chen Wenzhe truly understood that the emergence of the concept of Ru porcelain's azure color was inseparable from Song Huizong's pursuit of art.
However, the actual firing of porcelain with this color benefited from the wisdom and skills of Ruzhou porcelain craftsmen.
After seeing the production process of Ru kiln porcelain, Chen Wenzhe truly understood the importance of agate glazing.
Combining some modern research, Chen Wenzhe has a clearer understanding of the problems inside.
There are many reasons for agate to be glazed. The first one must be understood by ancient ceramic enthusiasts. The biggest difference between northern enamel and southern enamel is that the north has low silicon, high aluminum, and high-temperature kilns;
In the south, there is high silicon and low aluminum, and the firing temperature is relatively low.
The firing temperature of northern glaze is high. High firing temperature will cause the porcelain body to be heavy in color, which is not conducive to obtaining azure color. However, after agate is added to the glaze, this situation will be improved.
The main component of agate is silica. Adding agate to the glaze can increase the silicon content in the glaze, while reducing the proportion of aluminum and lowering the firing temperature of the glaze.
At the same time, it can also control the color of the porcelain body. You must know that the higher the firing temperature, the darker the color of the porcelain body. These characteristics are more conducive to obtaining azure color.
In addition to this, adding agate to the glaze can also affect the enamel.
The enamel of Ru porcelain is a typical lime glaze, and the content of calcium oxide, a cosolvent in the glaze, reaches about 15%.
If agate is not added to the glaze, in order to obtain the azure glaze color and the firing temperature is lowered, the glaze will not be burned through and the body will not be fired.
At high temperatures, exceeding 1220°C, it is easy to burn into a vitreous glaze and does not have the opalescent jade quality.
Moreover, the iron oxide content in your porcelain glaze is as high as 2% or more.
This is comparable to the glaze of the Southern Song Dynasty official kiln and Longquan kiln, both of which have higher iron content and the thickness of the glaze is not as thick as them.
In a high-temperature reducing atmosphere, where ionic iron is abundant and the glaze is fully melted, only a green vitreous glaze can be obtained, and the azure opalescent jade texture cannot be obtained.
The addition of agate to Ru glaze lowers the firing temperature of the glaze, which is beneficial to obtaining a milky jade-like glaze.
How could Chen Wenzhe know these things if he didn't see them with his own eyes?
Of course, the ancients definitely didn't know the reason, but through long-term practice, they slowly figured out the best firing formula and technology.