[TheForge] didymium glasses?

[Justin Fellenz]

Thanks for this good writeup, Steven. I went looking for eyewear on a variety of sites and found "check with your eye care professional" on more than a few. I don't know any opthalmologists that I can just ask a question of nor any who have ever forge welded anything. So this is valuable info.
   
  Cheers,
   
  JRF

Stephen Viola <stephen.viola at gmail.com> wrote:
  Here is some interesting information about this topic: (written by
some 'pot heads' (ceramic workers), but the basic principles apply)

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"
originated (1700's).

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 filters. 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.

Wombat
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