How Do Sunglass Lenses Get Their Color?

_{Article first published: June 2022}

From blue, green, gray, red or yellow to two-toned gradients – no matter what the color, there are countless options when choosing sun protection for the eyes. But how do sunglass lenses actually get their color? To sum it up in simple terms, there are two methods: using colored material or by tinting clear eyeglass lenses in a temperature-controlled dye bath. Read on to find out more.

Sunglasses designed for sports like skiing and cycling often come in functional colors, special shapes and non-standard sizes as well as special features, such as contrast sensitivity in the snow. In the fashion world, there are hardly any limits when it comes to tinting, with possibilities including color gradients, and two or even three colors on each lens. ZEISS has specialized in the industrial production of non-prescription sunglass lenses for precisely these applications at its Italian plant in Varese near Milan (ZEISS Sunlens). Around a thousand different colors are offered as standard at the plant. And customers, including high-end brands like Lindberg and Andy Wolf consult on the individual colors that are possible.

How are the colors for the sunglass lenses determined in this case? A device known as a spectrophotometer can be used to define the color of a specific sample such as an existing sunglass lens or potentially a fabric or similar material. The color is then replicated with absolute precision. Alternatively, sunglass designers describe the color in words or refer to a Pantone color, for example. Whatever the customer's preferred color, ZEISS Sun has the capability to create the right mix.
The question of how exactly the tint is then applied to the lenses depends on the intended purpose of the finished eyeglasses and the frame of the lens. This determines which material is used (see info box), and this in turn dictates the tinting process.

Once a color is defined, the right blend of dyes is mixed with the raw (synthetic) material for the eyeglass lenses – usually in the form of pellets – in large industrial containers. These two components, the dye and the material, are then melted down and hardened again. This results in colored raw material pellets.

This colored raw material is melted down in turn and then pressed into what are known as molds for eyeglass lenses in the particular shape required. These colored eyeglass lenses are then hard coated and other coatings such as mirroring can be applied if required. Over 500 different options in a wide range of colors and intensities are available. The quality check and marking with the discreet ZEISS laser engraving are an obligatory step for each individual eyeglass lens.

With this method, the eyeglass lens has already been processed into a semi-finished state. The experts start by mixing a specific dye that is measured to the millimeter in powdered form and then dissolved in an immersion bath.

These heated tinting baths (approx. 90°C) hold a wide spectrum of different dyes. The eyeglass lenses are immersed for a defined period of time depending on the desired color and intensity. This method also makes it possible to apply color gradients or several colors to each eyeglass lens – depending on which side is immersed and at what depth. After this, the lenses are rinsed briefly, sometimes also placed in a hard coating bath and then finished as described above, for example with mirror coatings. It goes without saying that the engraving and quality check are key steps here as well.

What's more, and depending on the final tint, this method can also be used to apply a second color in the form of a gradient to tinted eyeglass lenses that have been previously fabricated via the material mix. Self-tinting eyeglass lenses can be slightly pre-tinted or given a gradient that moves from color to clear and thus combine the advantages of photochromy with constant sun and glare protection, like that provided by ZEISS AdaptiveSun.

ZEISS operates dye works for prescription glasses, i.e. corrective lenses, at all its production locations in America, Europe and Asia. The basic elements of the process have already been described – here too, the eyeglass lenses are tinted in a tinting bath. Once an eyeglass lens has been fabricated to its genuine round shape with the correct, individual visual correction, it makes its way to the dye works. The various dyes are mixed directly on site. Which means there is nothing preventing a pair of individual, custom-made progressive lenses from now being produced as sunglasses with the desired tint. This method is also used to color stock lenses before coating.

The dyeing process is carried out by hand, and instinct and long-standing experience play an indispensable role in this process. Every lens made in prescription production is unique, and the dyeing times vary accordingly. The results of the dyeing have to be exactly the same for the right and left lenses and is always checked under a daylight lamp. Even color gradients are dyed and examined by hand. Based on this, special tints and gradients can also be implemented for sunglass lenses with the individual prescription. It is also interesting to note that the dye works tend to be staffed by women – given that color vision deficiencies and color blindness are inherited via the Y-chromosome, it's men who are primarily affected by these limitations.

In fact, everyone who wears regular corrective spectacles and does not use self-tinting glasses also needs prescription sunglasses. Applications vary to a significant extent. Glare protection is especially relevant in terms of safety while driving and is indispensable during hiking, water sports and other outdoor activities. Whenever there is glare from the sun, the sunglasses provide relief for the wearer. And why shouldn't people who wear glasses have a fashionable pair of sunglasses with a special color gradient or mirroring too? Read everything you need to know about prescription sunglasses here. An eye care professional can provide advice on which tinted prescription eyeglasses lenses are the best match for which situation.

Self-tinting eyeglass lenses are a special case given that they are initially clear, i.e. transparent, and only become dark when they come into contact with UV radiation. Self-tinting eyeglass lenses contain phototropic molecules that change shape when activated by contact with UV radiation. In other words, they are not dyed but rather have a special material characteristic. This method is used for both ZEISS PhotoFusion X as well as for the ZEISS AdaptiveSun intelligent eyeglass lenses that are already produced with an initial tint but then become even darker depending on the strength of the UV radiation.