Final answer:
A vitreous layer or coating fused to a clay body, known as glaze, is mainly used for strengthening the surface of the ceramic piece, making it more durable and less porous. It also serves a decorative purpose with its array of colors and finishes.
Step-by-step explanation:
A vitreous layer or coating fused to a clay body is most commonly known as glaze. The purpose of this glaze is to serve a few important functions in ceramics:
- Strengthening the surface of the ceramic by making it harder and more durable.
- Creating a non-porous layer that makes the piece less absorbent and more waterproof.
- Decorating the surface, since glazes can come in a variety of colors and finishes that can enhance the visual appeal of the piece.
In response to the question, the primary use of a vitreous layer or coating fused to a clay body is to function as a form of strengthening the surface of the clay object. It can also enable the clay object to hold liquids by making its surface water-resistant, effectively decreasing waterproofing. Options a, c, and d are also valid to a lesser extent, though the key purpose is b, strengthening the surface.