This invention relates to methods for embossing a pattern in a piece of glass.
Hot glass is a relatively sticky material that tends to adhere to hot embossing tools. In the manufacture of glass articles, this sticking tendency is controlled by working the hot glass with chilled tools. Fine detail however, cannot be embossed in glass with chilled tools because a skin forms on the surface of the glass, which limits the fineness of the pattern than can be impressed. This skin inhibits the flow of the glass into the small detail of the embossing die.
If the die temperature is increased to permit a greater glass flow, a condition will be reached where the glass will adhere to the tool making the embossing impossible. The adherence of molten glass to mold surfaces has been reduced by vibrating the mold while the glass was in contact with the mold as shown in U.S. Pat. No. 1,482,760 issued on Aug. 9, 1922 to J. A. Milliken. This vibration was heretofore used to eliminate the necessity for cooling the mold between separate molding operations. Carbon and graphite die materials have nonstick properties that permit their utilization in glass forming. However, these materials cannot be employed to emboss fine patterns because the details in the patterns are destroyed by the oxidation of the materials at high temperature.