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

Mon Feb 13 20:15:59 EST 2006

Hey Mike,
The background color is blue green.
I looked at some scratches of the gold layer where it was scraped away from 
the plastic below it, with my stereo microscope and can't detect a clear 
layer.
It looks like the gold was vacuum deposited directly on the  Didymium 
plastic material.
Chuck
----- Original Message ----- 
From: "Mike Porter" <michael.a.porter at comcast.net>
To: "Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Sunday, February 12, 2006 3:37 PM
Subject: Re: [TheForge] Re: Subject: Didymium? I say "no way."


> 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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