[TheForge] Re: Subject: Didymium? I say "no way."

Sun Feb 12 16:37:19 EST 2006

Chuck,
Thank you. This kind of reply is what pays me back for the time spent 
writing technical emails to news groups. Two more things you could tell me 
are: (1) Is the gold layer deposited on a green polycarbonate film or on 
clear and; (2) Is the background color viewed a blue-green or something 
else? I have already seen the NIOSH report you mentioned. It has become a 
permanent presence on the Net, and is pretty enlightening for a government 
document.

Bailey Pottery is a good company to look to first, whenever you want to get 
a line on cutting edge products for heating work. Someone there keeps a 
close eye on technological changes. They even wanted to carry Gas Burners, 
but couldn't cut a good enough deal with the publisher.

Gold deposits on polycarbonate reflect IR. What wavelengths and how much is 
disputed back and forth between various 'experts' who have commercial axes 
to grind. I would love to find out more about it, and will write to Mr. Gene 
Moss to see if he has S.E.D graphs available. I will also write to the 
manufacturer for the same information. Sometimes they are very obliging, but 
are more often are into obfuscation.

Here's the deal; infrared radiation stretches clear from 700nm (or 760nm, or 
780nm depending on which source is disputing the point), up to 3000nm. 780nm 
to 2000nm is the optical band of concern set by NIOSH (but that will almost 
certainly be reduced to 700nm in the next few years). Industry standard uses 
400nm to 700nm as the visible light band.

The ultraviolet spectrum stretches from 10nm to 380nm or 400nm depending on 
the expert. NIOSH is slowly folding the last 20nm into the UVA (near) range. 
It is now listed as far blue light or as near UV depending on the document 
in question. However it is treated in a special near UV category. The UV 
ranges of concern to NIOSH are far UV (UVC) with stretches from 200nm to 
280nm, mid UV (UVB) from 280 to 315nm, and near UV (UVA) which includes 
everything from 315nm to 385nm or 400nm, depending :-) Physicists prefer: 
UVA 400nm to 320nm; UVB 320nm to 290nm; UVC 320nm to 100nm.

Did you notice that 10nm to 200nm isn't of any concern  to NIOSH? The ocular 
range of radiant hazard is set from 200nm through 2000nm. That can change 
any time the experts who sit on safety comities gain new information giving 
them a reason to go through that much trouble.

I'll bet you also noticed that, even though IR comes in three bands: Near 
(NIR); mid (MIR); and far (FIR) that I didn't give any cut off points at 
all--not even tentative. This is because infrared is part of the 
communications bands, and everything about it is disputed. It's a political 
football; a turf war, with BIG money involved in where the lines are 
permanently drawn.

The practical points are that the UV spectrum is much shorter and better 
defined than the IR spectrum, even though UV definitions are pretty 
imprecise. So, we can have a "consensus of opinion" that allows statements 
like clear polycarbonate safety glasses as thick as .92" in their thinnest 
cross section will block 99.9% (or 99.97%, which is quoted by another 
manufacturer) of UVA and UVB. UVC blocking takes special tints or additives. 
When you read a statement like "blocks UV completely," you are hearing 
double talk. This is even more true for statements about IR, especially, 
when it is exchanged for terms like heat blocking. Well, we all grew up 
listening to TV hype, so why should we be surprised that the truth is never 
so pretty as commercial descriptions would lead us to believe?

For me it means months more of digging into the question of gold deposits on 
filter plates and spectacles, and for you it means always translating 
commercial certainties to probabilities in your mind, while deleting 
everything else and sending it the recycle bin of "hoped for truths."
Mike P.

----- Original Message ----- 
From: "Chuck Robinson" <robi5515 at bellsouth.net>
To: "Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Saturday, February 11, 2006 4:02 PM
Subject: Re: [TheForge] Re: Subject: Didymium? I say "no way."

> Hey Mike,
> I have a full face shield that Jim Schell sold me about 10 years ago. It 
> is similar to the one in the below link:
> http://www.baileypottery.com/safetyequip/eyesafety.htm
> The main advantage is, it eliminates the sodium flare, so I can see my 
> billet much more clearly and easily detect any welding voids.  Almost like 
> having X-Ray vision The gold filters out the IR so effectively that the 
> heat is almost completely blocked.
> The gold also does this without reducing your  ability to see what you are 
> doing when not looking directly into the fire, the way standard green 
> filter lenses do.
> As has been said before, the main disadvantage is that the gold layer is 
> fragile, and the shields are expensive.
>
> Jim Schell was involved in some of the NIOSH studies done on this subject 
> about15 years ago He sent me this in an email:
> ........... My contact at NIOSH
> is:  Mr. Gene Moss-NIOSH-MS-R-13, 4676 Columbia Drive, Cincinnati, OH, 
> 45226
> phone:  (513) 841-4374.
> I do not have any way to address Doug Learn's comments about UV emissions
> from gas or coal forges.  However, while at my studio here in Houston, 
> NIOSH
> did check for UV and IR emissions from my electric kilns, propane glory
> holes and propane/oxygen torch.  Gene Moss can address each of these areas
> for you or you can see his report:  HETA 95-0119-2554.  Doug Learn's
> comments about genuine didymium being only in glass spectacles is correct.
> The polycarbonate spectacles and faceshields I have incorporate a
> "didymium-like" material that mimic's the effects of didymium glass.  The
> goal of reducing the yellow sodium flare in didymium polycarbonate lenses 
> is
> almost the same as in genuine didymium glass.  The polycarbonate lenses 
> are
> much lighter, cost less and are less fragile.
> JIM SCHELL
> -----Original Message-----
> From: Chuck Robinson <crobin at datastar.net>
> To: Jim SCHELL <jhschell at ix.netcom.com>
> Date: Thursday, April 09, 1998 1:59 PM
> Subject: Fw: Didymium glasses and UV/IR protection)
>
>
> Chuck
>
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