The worlds first stoneware glazes were developed during the Shang Dynasty in China (1,600 – 1,100 bce). This is an astounding feat when considering that stoneware was not achieved in Korea and Japan for another 2,000 years and in the West for another 3,000 years.
One theory for the early development of stoneware temperatures in southern China was that the clay being used at earthen ware temperatures was actually under fired stoneware bodies. Observation would have shown that these clays when fired hotter produced more durable ceramic. The glaze was likely another observation of the process already being employed, wood ash fluxing at higher temperatures would have lightly glazed both the pots and the interior of the kiln. It would have been a simple assumption to begin testing wood ash mixtures and developing glazes.
These early glazes, being based on the variable material wood ash, have a wide variety and composition. In addition to the innovation of glaze and kiln design allowing the higher temperatures, the Shang also began the pursuit of Chinese porcelain. This proto porcelain as it is known is made from a kaolin bearing stoneware. The pieces were modeled after The bronze vessels being produced at the time and were lightly glazed with the same ash glazes common at the time.
This type of glazing persisted through the Han Dynasty, techniques and form being refined through the generations.
Unlike the high fire glazing tradition of most early cultures, the first Chinese stoneware were composed primarily of clay and calcia, rather than feldspars, in the form of limestone, but also derived from wood ash and sometimes crushed shells. The composition of these glazes were Silica, alumina, and calcium carbonate. The silica and alumina were provided by the clays and the ash or limestone was the second ingredient. The glazes were usually yellow to green and were colored by incidental trace amounts of titanium and iron in the clays used in the mixture. There was also a range of surface qualities that were largely dependent on firing and cooling speed. The more matte glazes were fired and cooled more slowly allowing calcium crystals to grow.
Over time the ash in the glaze was largely replaced with limestone, though it is likely that wood ash was used in some combination throughout the early history of Chinese glazes.
The height of these stoneware glazes were achieved in the Yue wares which were made during the Five Dynasties Period in the early 10th century ce. These works are revered for their refinement and beauty.
From these simple beginnings, the tradition of Chinese stoneware and porcelain glazes unfolds and reaches its great peak during the Song Dynasty. From elegant celadons to rich temmoku’s the potters of the Song were some of the most accomplished in the history of ceramics. 
I used Chinese Glazes; Their Origins, Chemistry and Recreation by Nigel Wood and 10,000 Years of Pottery by Emmanuel Cooper for sources in this post