Is a 0.5 cm thick obsidian plate good to see the Sun directly?


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NO. Do not trust your eyesight to anything other than a product that has been specifically designed to protect it.

For a good starter resource on eye safety for seeing the Sun, see e.g. this AAS eclipse-viewing resource. Use only certified Sun-viewing eyeglasses, or welding glasses of shades 12 or 14 $-$ and only purchase either of those from a reputable vendor.

If the object you have in your hand is

0.5 cm thick obsidian plate,

and that is all that you can tell us about it, then it is not safe to use for solar viewing. Obsidian is a type of glass and, like all naturally-occurring glass, there's a substantial amount of variability in its properties. The only way to tell whether a specific sample is safe to use is to measure directly how much UV light it lets through: it is the UV light that causes the most damage, and you cannot see it with the naked eye.

What are the risks of using unsafe products (or using products not certified to be safe, which is the same thing as unsafe products) to view the Sun? You risk losing your eyesight, and it's simply not worth the risk.

  • $\begingroup$ Thanks, yes I prefer to be safe than sorrow. I saw a paper "Radiative thermal conductivity in obsidian and estimates of heat transfer in magma bodies" (1981) by Judy Stein that says that it absorbs in the 400 nm range and the uv that passes the ozone layer is from 350 nm to 400 nm, so I thought it could be safe in that range for Sun viewing, but as I said, I prefer not to risk my eyes and be safe than sorrow. Thanks again. $\endgroup$ – Gndk Mar 25 at 16:04

I wouldn't risk my eyes on some random chunk of obsidian with an unknown absorption spectrum. It might look dark, but that tells you nothing about its absorption of ultraviolet.

Retinal sunburn is not fun. Get a proper viewer.


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