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Spectacle frames are manufactured from either plastic or metals-usually nickel-silver, monel and high-nickel. The ratio of metal to plastic frames varies with fashion trends. At this writing, it appears that 70 to 80 percent of the frames are of the metal variety. A fairly large percentage of these are gold plated to achieve a yellowish finish. The rest either are nickel, chromium or rhodium plated to realize a white finish. Manufacturers of optical frames started to switch from goldfilled to electroplated gold during the mid-1960s, primarily for cost savings. At that time, they deposited 2~5㎛ of a bright nickel on the nickel-silver substrate to yield a quality finish. After the nickel deposit, the frames were preplated with a gold strike and the gold electroplated topcoat was applied. usually at a thickness of 3 to 5 ㎛. This thickness was sufficient to prevent attack through the gold to the base metal as a result of perspiration or cosmetic by the user. However, towards the mid-1970s, gold thickness sometimes was reduced to less than 1 ㎛ due to the high price of the metal. Pitting of the substrate resulting from perspiration or cosmetic became fairly common, especially in areas where humidity and temperatures were high. Some manufacturers did increase the total gold Thickness to overcome these problems, whereas others chose duplex plating of palladidm-gold alloy topcoated with a layer of hard acid gold to achieve the final desired color. Still others currently are evaluating organic coatings. Many optical frame manufacturers supply goods in a slightly pinkish flesh tone. Because these colors cannot be attained with the acid hard gold baths, these manufacturers must utilized color gold for the final desired tone. Again, the thickness of these color golds is less than 0.2 ㎛ which means they give the final color, and afford corrosion protection and wear resistance.
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