Gold-filled eyeglasses used to be very popular before the early 1970's, and as far back as 150 years ago. Gold fill involves a process that allows a thick layer of gold to adhere to eyeglass frames, which provide sharp surface shine and protection against the elements. Gold was cheaper before the early 1970's, until President Richard Nixon removed the U.S. from the Gold Standard. Vintage and antique eyeglass were often manufactured with the gold-filled process, and some companies continue to make eyeglasses in gold-filled designs today.
The process of gold-filled manufacturing, as it pertains to eyeglasses and other jewelry, has also been called "rolled gold," "metal cladding," or "gold overlay." The industry produces hollow tubing, wire and gold- filled stock which comes in sheets, to overlay a base metal with an appropriate thickness of white or yellow gold. Do not confuse the term "gold-filled" with "gold plating," which involves a much thinner layer of gold to the frame by using chemical and electronic processes for adhesion.
Manufacturing -- Welding.
A crafstman places a thin sheet of gold metal, in the desired thickness and karat purity, over the base metal, usually made of brass or nickel. They transfer them to a an air-tight steel furnace chamber. The edges of the two opposing metals (frame and gold) receive a flux paste to guard against oxidation and impurities. The temperature of the enclosed furnace must be raised to about 900 degrees centigrade to quickly melt or weld the metals together.
Manufacturing -- Pressing
The metals then are pressed at abut 2500 psi (pounds per square inch) in an industrial hydraulic press immediately after their removal from the furnace. The crushing force causes an "alloy diffusion," where the atoms of one metal diffuse or bleed into the atoms of the other, forming a tight metallurgical bond. In essence, the metals become one material.
Manufacturing -- Rolling
After the metals join, they need to be rolled in a rolling mill. The rolling mill press, combined with additional heat for annealing or softening the metal, further compresses the gold fill material into the base metal. This produces a melding or welding bond so strong that the gold filled layer can be bent and formed into any configuration, without it de-laminating or detaching from the base metal. Workmen can also solder it without deformation or damage.
Round and Wire Gold Fill for Eyeglass Frames
Eyeglass frames typically receive a type of round or wire gold fill that completely surrounds the core base metal around the frame, but the same welding, pressing and milling process remains the same. Eyeglass frames that have square or rectangular shapes can be "cladded" with one or two layers. A single clad layer of gold filled sheet can be applied to one side of the eyeglass frames, typically the side that shows on the outside.
Gold Filled Thickness and Karat
The thickness layer for eyeglasses, depends upon the usage. High usage items such as pocket watch cases and cigarette lighters can receive layer thicknesses from 75 to 400 microns, whereas eyeglasses can hold up well to thicknesses ranging in the 15 and 30 micron range. White or yellow gold comprises most types, and the purity can range from 10 to 18 karats, discounting custom pieces which might be higher in fineness.
Gold-filled eyeglasses sold on the commercial market, designated as gold-filled or "rolled," must adhere to the definitions prescribed by the FTC (Federal Trade Commission) standards. The total amount of gold used in the piece or object must contain 1/20th of the finished item's weight.
Gold Filled Advantages
Virtually any thickness, color type and karat purity can be used in eyeglasses. Different base metals can produce stronger gold filled coverings, able to withstand more form-ability and manipulation. Gold-filled eyeglasses stand up to wear better than plated gold coverings, because of their thickness, welding and pressing process. Gold-filled frames can last up to 75 years without seeing any noticeable signs of wear or deterioration. Gold-filled eyeglass frames offer a surface that can be polished repeatedly, or repaired if scratched.
Types of Eyeglasses
Gold-filled eyeglasses can come in classic styles, composed of round, rimless, rectangular or oval frame designs. Some can come with nose pads or without them. Many antique and vintage reproductions can be made to custom order. Many eyeglass frames can receive treatments to guard against hypoallergenic skin irritation and conditions.