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How are glasses manufactured?
We often take the most basic things we enjoy for granted. We are able to enjoy improved vision through wearing glasses today because of the innovation of others throughout history. Some of the first spectacles were simply glass magnifiers that were held by hand.
While glass was once used to manufacture lenses and metal was mostly used for frames, materials that are lighter, more versatile and easier to work with now mean that the glasses manufacturing process is now faster, cheaper and can be automated. Bone, ivory, leather and even tortoise shells were once commonly used to make frames to house lenses.
While the glasses manufacturing process may need human hands at specific points, much more of it is now automated, meaning your glasses can be manufactured and sent to you a lot faster.
What are glasses frames made from?
Most frames are either made of a plastic or metal material. One of the most popular materials used for manufacturing glasses is acetate, so we'll focus on this as part of explaining the glasses manufacturing process.
How glasses frames are manufactured
Most plastic frames are made from acetate. Acetate is light, durable and is derived from bioplastic cellulose acetate. This is a natural material compound that is extracted from the fibres of cotton balls or wood pulp.
The cellulose acetate goes through several processes, including organic synthesis, where the purified cellulose is mixed with acetic acid. This creates the compound we then call 'cellulose acetate'.
In this phase, the cellulose acetate is easy to manipulate, and dyes can be added to the compound depending on the end desired style and the cellulose acetate is then cut into thin sheets of acetate. This also known as routing.
The front of the lenses are cut from the acetate using machinery, although in some cases, some handy work is done. The process includes heating to create the curvature of the frames so that the lenses can sit comfortably.
A metal rod is sometimes inserted into the core of the temple for reinforcement. You can sometimes see the core if the frames have some level of transparency.
Manufacturing lenses for glasses
Modern-day lenses for glasses are made using a mixture of science, technology and art. The varying prescriptions and frame sizes means every lens has a different curvature.
How are lenses for glasses manufactured?
Modern-day glass lenses are made from polycarbonate or CR39 plastic.
A technician selects a lens blank with the correct amount of existing curvature so that it corresponds with the patient's prescription. Using a lensometer (also known as a focimeter), the patients optical centre is marked. This will be the exact point that sits over the patient’s pupil.
How are coatings added to lenses?
The coatings for the lenses are added by several different methods. One is by dipping the lenses into heated metal bins filled with the desired treatment/tint. Spraying on the coating is another method. The lens then gets exposed to high heat for a prolonged time resulting in the hardening of the liquid and adhering to the lens
Another process is to built-in the coating at time of lens manufacturing. Advantage is that it gets distributed evenly.
Common treatments include ultra-violent tints, scratch-resistant and reflective anti-glare coatings. Scratch resistant coating is important, especially for plastic lenses as the material is softer and therefore more likely to scratch.
The lens then goes through a grinding and blocking process, where it is perfectly moulded into the correct shape and curved, matching the patient’s prescription, and fitted into the frame
The lens will then go through a quality control check to ensure there are no scratches, cracks or chips and that the correct prescription has been applied to the lens.
The individual parts of the glasses can now be affixed and put together to produce the final frame.