Summer's in-colors are apricot, mint, citrus and sea blue, but sunglasses are usually tinted brown, gray or green. The reason is that these are the colors which distort color perception the least. When lenses are tinted with other colors, the brain requires a certain length of time to neutralize the shade distorted by the glasses. Therefore, it perceives colors differently.
But how do the lenses actually get colored in the first place? There are many different procedures, depending on whether the lenses are made of plastic or glass.
Glass lenses are tinted through the vacuum deposition of absorbent coatings. These thin coatings consist of metal or metal oxide mixtures and may be deposited at specific high temperatures only. They also have a high refractive index, therefore the reflectance is increased. They are deposited in multiple layers so that the properties of the glass remain intact. Due to the tinting of the metal or metal oxide mixtures, these lenses are available only in brown shades of different levels of absorption.
Almost all plastic lenses are tinted in a special dye bath. To do this, several lenses are mounted on special holders, then plunged into the bath. While the lenses are in the immersion bath, the color particles penetrate about 0.1 millimeter into the surface of the lens, becoming firmly embedded in it. Each plunge basin is equipped with a magnetic stirrer which ensures that all lenses are tinted evenly. Color substances which are also have applications in the textile industry are used in this process.
In accordance with a color sample, plastic lenses may be tinted to any conceivable color and light reduction level — based on the primary colors red, yellow and blue. Lenses with gradient colors may also be produced using special equipment: by setting a pre-determined exchange speed for the eyeglass lenses, tints which transition gradually from light to dark may be achieved. Thus, not only the frames, but also the lens tint may now be chosen, to personalize the final eyeglasses — even if this means that not all colors can be perceived in their original shade.
June 13, 2012