A heat-proof material, Fire-King glassware is made of a chemical substance called borosilicate --- a soft glass, the likes of which are normally used for items such as glass bowls. Durable and strong, this material has even been used to store nuclear residue. Prominent in science labs in the form of beakers and test tubes, borosilicate uses particles of boron oxide to replace the soda and lime particles typically found in the soft glass variety. This boron oxide is an adhesive that keeps the silicate particles bonded together, along with aluminum oxide and sodium oxide. These boron oxide components' small size causes the silicate to group tightly together, which strengthens the glass considerably.
Fire-King glass has extremely clean lines, which made it popular for use by other companies for branding purposes. Companies such as McDonald's and Pillsbury have offered items made of the special glass as giveaways printed with their respective logos.
Collectors of glassware sometimes have a great deal of trouble with the proper identification of pieces. One of the included aspects of Fire-King glassware is its distinct markings. Fire-King pieces are branded or labeled with the word "Fire-King." Over the decades, the markings have included the company name and more specifications, but as of 2011 the word Fire-King has always applied. The small percentage not branded carries an identification label for the pieces.
Since the 1930s, Anchor Hocking developed a large collection of colors for the Fire-King glass that included Forest Green, Ivory and Jade-ite --- also green but quite opaque. The company also produced a color called peach luster and others with names such as Royal Ruby and Sapphire Blue. It also produced plain white glass printed with designs.