The art of enameling began to take form in the early Byzantine era, but borax was not used in the frits applied to metals until the middle of the 18th century. The early borate-containing frits were colored ground glass used almost entirely for decorative purposes, and then in small quantities. The main increase in the use of borax did not come about until the enameling of iron created a new industry in the 19th century.
Enamel was first applied to sheet iron and steel in Austria and Germany about 1850. Cast-iron shapes, such as cooking pots, were pre-heated in furnaces. Frit was dusted onto the hot metal as a dry powder, which sintered and stuck to the iron. The article was then returned to the furnace where the enamel melted to a smooth glaze. In this way, several coats of glass were normally added one by one to achieve the desired color and finish.
The enamel frits had to be easily fusible, and borax became an important ingredient. By the end of the century, a worldwide trade had developed in all kinds of household goods, as well as durable advertisement displays and signs of all kinds.
Ceramics glazing and decoration
The history of glazing, starting with the ancient Egyptian, Chinese, Babylonian, and Greek civilizations, is lengthy and complex. The earliest evidence of boric oxide (B2O3) use comes from China during the Liao dynasty (916 to 1125 CE). In recently discovered green shards, the glaze contains 13% boric oxide. The next examples come half a millennium later in the reign of Kangxi in China (1662 to 1722) and in Japan in 1699.
During the 18th century, potters and glassmakers in many parts of the world began to gain knowledge about the glazing properties of borax, but its price—£750 a ton in London in 1750—remained far too high for general application. Then in the 19th century, technical developments in the ceramics industries coincided with new borate discoveries in Italy, Turkey, and the Americas, which led to substantial reductions in price. Borax cost less than £100 a ton in 1850, and less than £20 by the 1890s. For the first time in history, borax became viable for modestly priced, mass-produced goods.
Benefits of borax
For glazes and enamels, boric oxide is unique in that it acts simultaneously as a glass former, as a flux, and as a viscosity stabilizer that prevents the glaze from running too much while it is being fired. Perhaps most important of all, boric oxide reduces the thermal expansion of the glaze so that it can be matched to the expansion of the underlying ceramic or metallic body. At the same time, it improves aqueous and chemical durability while adding to the brilliance of the glaze.