One of the earliest uses of borates is the production of glazes and frits to impart color and texture, as well as heat, chemical, or wear resistance to appliances, ceramics and tiles. Boron assists in the production of smooth, hard, resistant, blemishless ceramic surfaces.
Glazes are the thin, glassy coatings fused onto the surfaces of ceramic substrates such as wall and floor tiles, as well as tableware. Before they are used in glazes and enamels, borates are incorporated into frits to render them insoluble. Frits are materials of a glassy nature rich in silica, obtained by fusing different crystalline materials at high temperatures (more than 1100°C).
In glazes and enamels, borates are used to initiate glass formation and reduce glass viscosity. They also help to form a smooth surface and reduce thermal expansion. This facilitates the coating and a good fit between the glaze or enamel and the item it covers. Borates also increase the refractive index (or luster), enhance mechanical durability and resistance to chemicals, and help to dissolve coloring agents.
Recently, borates have become important ingredients in the manufacturing of ceramic tiles since they act as powerful binders, allowing manufacturers to reduce the thickness, use a wider range of clays, increase productivity and decrease energy usage.