How to tell if your glasses lenses are glass or plastic

When you receive a new set of glasses, chances are the material of the lenses isn’t the first thing on your mind. You might be preoccupied with your optometrist appointment, safeguarding your prescription, selecting frames, and considering extras like anti-reflective or anti-fog coatings. Once you’ve donned your new spectacles, the matter seems settled. Yet, the choice between plastic and glass lenses holds surprising significance in how you care for them, the products suitable for them, and their repairability in case of scratches or frame damage. Have you ever taken a moment to consider whether your personal lens crafter defaults to plastic or glass lenses?

Whether you’re scrutinizing your current eyewear or stumbling upon a vintage pair in your attic, determining if the lenses are plastic or glass doesn’t require a scientific background—just a few investigative tactics. Here are seven tried-and-tested methods to discern your lens material:

1. Sound Test:

Distinguishing between plastic and glass is often as simple as noting how the material responds to a light, sharp impact. Plastic, being softer, lacks the resonance of glass when struck. Glass emits a distinct ringing sound or a soft tink, while plastic typically yields a muffled thud, even with gentle taps. To conduct this test, use a small rounded metal object such as a penny or a wedding ring. Hold the glasses by one earpiece with two fingers to avoid interfering with resonance, and gently tap one of the lenses. A clear, high-pitched sound suggests glass, though it could also indicate very hard plastic.

2. Temperature Check:

Glass and plastic share many functions but exhibit notable differences. Beyond sound transmission, they respond differently to temperature variations. Glass, akin to smooth rock, efficiently retains heat and cold, unlike plastic, which tends to resist significant temperature changes. In cooler climates, glass lenses feel noticeably cold to the touch, while plastic remains neutral. To confirm, place the glasses in the fridge for about five minutes. If the lenses emerge cold, they likely comprise glass.

3. Count the Scratches:

Surface hardness stands as a major distinction between plastic and glass. While plastic’s inherent softness makes it resistant to shattering, it also renders it prone to scratching, prompting the inclusion of anti-scratch coatings. Older lenses might lack this protection, with numerous scratches suggesting an older model of plastic lenses.

4. Tooth Tap:

A popular and accessible method for discerning lens material involves tapping the lens against your teeth—a tool always at hand. Glass typically produces a soft ringing sound upon contact, while plastic elicits a subdued thunk. A ringing sound indicates glass, while a thunk confirms plastic.

5. Check the Weight:

Even when comparing identical, brand-new lenses with no scratches and similar sound responses, one method always reveals the truth. Glass lenses inherently weigh more than plastic, a characteristic contributing to their ability to achieve higher indexes. If the lenses significantly outweigh the frames, they likely consist of glass.

6. Consult an Optician:

When uncertainty persists or you require assurance before using products rated for specific lens materials, consult an optician—a professional well-versed in lens intricacies. Opticians possess expertise in assisting individuals with frame selection, determining focus centering, and fitting glasses. Their familiarity with high index lens types, specific materials, and coating combinations ensures reliable identification of lens materials.

7. Scratch Resistance Test:

For those willing to experiment, a final method involves testing scratch resistance. Rather than relying on visual inspection alone, use a small sharp knife to mark the edge of a lens. Easily created scratches indicate plastic, while resistance suggests glass or hard plastic.

By employing these techniques, you can confidently identify the material composition of your lenses.

Remember, understanding the material—be it glass or plastic—guides you in selecting appropriate cleaning products, handling techniques, and repair solutions. And when in doubt, don’t hesitate to seek guidance from opticians, the experts in all things lenses. With these techniques at your disposal, you can confidently navigate the world of eyewear, safeguarding your vision and enhancing your optical experience. If you have any further questions or need assistance, feel free to reach out to us anytime.