The subject of plumbing fixtures is so broad that we are going to limit our coverage this month to the most basic aspect -- an overview of the materials commonly used in making them.
This is an updated version of the product training course introduced by Supply House Times in 1979, authored by Don Arnold.
Vitreous China
The term "vitreous" in connec-tion with china today concerns the manufacturing process in which molded fixtures are baked at extremely high temperatures, re-sulting in a material that is strong, nonporous and impervious to absorption. Though in general, the word "vitreous" means "glass-like," it is important to under-stand that, in plumbing china, the word is used in reference to the en-tire fixture, not just the surface glaze. The raw materials used to make china are basically a combination of special clays, mixed with a few other ingredients such as flint and feldspar, mixed in exact proportions with water (a mixture called "slip."). The slip is poured into a mold, conforming to the shape provided. The mold, be-ing a very porous material, absorbs water from the slip, resulting in a buildup of solid, semi-dry clay against its walls. After further curing, the clay so-lidification develops to the point where the product can be removed from the mold, and then cleaned up and com-pletely dried (but not yet heated). The next stop for the newly formed fixture is the glazing sta-tion, where a liquid similar to slip is sprayed in a thin, even layer over all exposed sur-faces. Color, if any, is combined with this glaze application. The coated fixture is then placed onto a car that slowly moves through a tunnel kiln (oven), transforming it into a solid, strong and nonporous struc-ture with a glassy permanent bond on the surface.