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How are glasses glazed or reglazed? by james Styles
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How are glasses glazed or reglazed? |
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Health,Seniors,Recreation & Leisure
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There are many different materials that used in the modern construction of glasses and spectacles. The glasses frames themselves come in a large assortment of styles, colours and materials - but selection of which glasses frame to choose is mostly down to personal style selection and cost. The lenses for glazing or reglazing glasses and spectacles however come in an equally dizzying array of materials, each of which has its own attributes but also has specific properties that make it suitable for glazing glasses lenses for a particular purpose. The most popular glasses lens in use today goes by the description of CR39 glasses lens material - which obviously doesn't tell the consumer much about what kind of glasses he or she will be receiving or what the benefits of glazing with that lens material may be. The term CR39 actually comes as an abbreviation of "Columbia Resin #39," which has its origins in the late 1930's America when a company called Columbia Southern Chemical Company had been tasked with developing a material suitable for oophthalmic lenses. The team investigated many compounds and resins until finally arriving at its 39th attempt - a resin that had good structure, thermal properties and relatively easy to manufacture. Instead of making glasses though, it was originally combined with fiberglass and used to make aircraft components such as fuel tanks (of course this was during WWII). Later in a search for peacetime use, several manufacturers started to develop CR39 as eyeglass lenses. It was a common "target" material as it had some specific properties that made it an excellent material for making glasses or spectacles from. It was able to be made in sufficiently large volumes that it became cheap to purchase, and when used in glasses were easily formed into spectacle lenses. As it was a hardened resin, it was highly resistant to lens scratching, was durable, had outstanding shelf-life (it did not degrade over time even when exposed to sunlight) - and of course had very good clarity. These glasses lenses are also very lightweight and less prone to shattering than glass which of course is important when the spectacles are worn on a regular basis and safety is always an issue when materials such as glass or even polycarbonate are in proximity to the eye. The biggest problem with CR-39 lenses in the early days of development was the shrinkage of the lens in manufacture that made it very difficult to actually cast a lens with a specific power and so address a prescription for glasses. This became the biggest barrier to widespread success of the material for making glasses until the late 1940's when a new way of casting the glasses lens was developed as well as a suitable process for grinding and surfacing the lenses to make them accurate and suitable for making spectacles from. From that point there was a constant stream of improvements to the material itself as well as the manufacturing processes used to convert the blank lenses into optical lenses to correct vision - issues such as lens coatings, further hardening of the surface and improvement in quality all continued to make the CR-39 lens material the dominat choice for making spectacles for over forty years.
Related Articles -
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