Five Vintage or Antique Black Glass Iridescent Buttons

Here a five black glass iridescent buttons. They probably date to the first half of the 20th century. They have a please design with a depressed or concave center with a stippled design around the edge. Four have an iridescent coating, and for some reason one does not. There is an optical illusion in some pictures where the center looks raised. The buttons are 5/8 inch or about 16 mm.