Glass that gradually shades from one color to another has ingredients such as uranium and gold, which are sensitive to heat. When part of the object is reheated, it "strikes" or changes color. Heat-sensitive glass became very popular in the late 19th century. Many companies used heat-sensitive glass to create a variety of products, sometimes imitating porcelain. A matte finish could be attained by exposing the glass to acid. Companies gave heat-sensitive glass exotic names like Amberina, Peachblow and Burmese. This video shows the 50th Annual Seminar on Glass session by William Gudenrath: An Investigation of Some Glass Decorating Techniques Used in Early 20th-Century American Factories.