
First produced in Venice, Italy in the 16th century, milk glass is made white by adding an opacifier - either tin dioxide or bone ash. In the United States, one of the premier manufacturers was the Westmoreland Specialty Company, founded in Pennsylvania by two brothers in 1889. Their focus was pressed glass and, in 1921, the name changed to Westmoreland Glass Company.

Milk glass of many colors was mass produced beginning in the 1940s. Pieces from the Victorian era are lighter and more finely detailed. The best way to tell the difference between an earlier piece and a mid 20th century piece is to hold the piece up to the sun. An older piece will glow pinkish at the edges and a new piece will show blue. I've tried to show you the pink glow in the photo below, but seeing it for yourself in real life is most illustrative. Once you compare two pieces, you'll be able to spot the difference easily.

The four legged covered jar below was made as a mustard pot, circa 1900. It has finely scrolled feet, a fluted and scalloped base and a lid with a crown finial. It still has remnants of its original paper label on the underside. The Westmoreland Specialty Company made lots and lots of different patterned mustard pots before closing their doors in 1984 and they are widely collected. The cherub plate with the openwork border is also circa 1900, but is missing its paper label.
Here's a shot of the label:
And a closeup of the crown finial:
One of my favorite milk glass pieces is a chipped up old covered box that long ago lost its lid. It's nothing to look at but I use it to hold makeup in my medicine cabinet and appreciate it every day.Be sure to stop by Faded Charm for more white!