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
, 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
. 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
, 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.