Here's an excerpt from an article in the Providence Journal about French milk glass.
Milk glass, an opaque white glass, was, of course, named for its color. The thick white glass was first popular from 1870 to 1880. It regained popularity in the 1920s and ’30s, and then in the 1950s to ’80s. Glass factories made thousands of covered dishes, pitchers, small trays and even figurines.
Milk glass was made in many colors in the United States and Europe, especially France. The descriptive terms “blue milk glass” or “black milk glass” are now used for some colored glass. The pieces are similar enough to be confusing. Portieux and Vallerysthal are two French names that appear on some colored milk glass made in the 20th century. The two companies merged in the 1970s.
One unusual sugar bowl made of blue milk glass by Portieux in 1933 has a cover shaped like a fat man’s head. He is smoking a pipe.
Much of the French milk glass from the early 1900s is quite attractive, and very collectible.