Didymium and didymium-variant filters (like the next-generation
AUR-92) are sodium flare (yellow) filters. They will remove the
yellow in the flame, they will remove the yellow flare that results
when the flame hits metals or glass. It is not a protective filter,
but a filter that allows you to see your work better. Didymium and
the variants do not filter IR to any great extent. Please don’t
confuse them with specific design lenses for filtering IR. Kiln and
furnace workers are exposed to much greater amounts of IR than torch
workers (unless you are working 2-3" in diameter or larger).
Damage to the eye from IR sources is cumulative. And it affects
people differently. There is some data that shows that people with
high content of melanin (skin colorant) have a higher resistance to
IR damage, meaning that it will take longer for them to show the
signs of IR injury than those that have lesser amounts of melanin.
For example, people of equatorial descent (lumping together a lot of
racial backgrounds, I know) like Mediterranean, African, Indian, etc.
typically have darker skin colors, and brown eyes. These people tend
to have less IR related eye injuries than a person of northern
European descent with fair skin and blue eyes. The classic case is
the glassblowers of Murano, Italy. For hundreds of years these people
have been blowing glass in front of furnaces and glory holes with
little historical evidence of eye damage. Compare that to the
glassblowers of old England, where there was a high level of eye
damage, in fact this is where the term "glassblowers cataract"
The eye does not have pain receptors for burns. The only indication
you have of over exposure to IR is dry itchy eyes, as the eye reacts
to the desiccation from the heat. In long term exposures, this will
lead to the development of retinal burns and corneal irritations
which lead to cataracts.
What does this mean to you? If your work is small soldering or doing
granulation, then didymium will help you see your work better. You
don’t have a massive IR exposure, but you should be aware of the
symptoms and take the necessary measures to protect yourself if your
work changes. If you are doing casting or enameling with a kiln or
furnace, or large, heat intensive work, then you need specific IR
It is a common misunderstanding that sunglasses are good to wear
while working in front of a kiln or torch, after all, sunlight is
hot, right? Sunglasses are about the worst thing you can wear, in
fact. Sunglasses typically do not filter IR. UV, yes, but UV is not
an issue for the work you are doing. Sunglasses pass IR, and with
your pupil wide open because you are working inside and the lenses
are so dark, your eye is getting blasted with IR.
I’ve read that a lot of metal workers have tried using welding
filters from the welding shop, but have found them to be too dark. A
welding supply shop is going to stock the items that welders need,
not necessarily the items that jewelers need. We have found that a
shade 2.0 filters 98% or better of the IR, while still allowing 40%
visible light. Compare this to a shade 5 (the usually available
filter) which filters 99% of IR and allows only 5% visible light.