From: dwilkins@orion.polaristel.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Didymium Glasses
Date: Sat, 03 Aug 1996 10:53:24 GMT

On 1 Aug 1996 21:39:31 GMT, darylb@bnr.ca (darylb) wrote:

>Just thought I'd relate todays experience at a scientific glass blower's place.
>He went to make something and said you better wear these and handed me
>some glasses. I thought they were safety glasses, in case of a splatter or
>something. He started heating up the glass against the gas torch and as I
>was watching he said take a look without the glasses and when I lowered
>them was slightly blinded by the flare of the burning gas etc and could no
>longer see what he was doing. Slip the glasses back up and everything was
>sharp and the flare gone.  
>
>Very impresive! The tint was so slight, just a bit blueish like shades,
>but the effect was radical. Comparable to the flare reduction with welding
>(shade5) glasses but without the darkening. That was the impressive part.
>I think I may get them for blacksmithing after all 8^)

You were blinded by the emission lines of sodium. Didymium is a name
given to a rare earth mixture. The glasses have a sharp absorption of
the sodium lines but are not very useful at other wavelengths.

I would not recommend these glasses for use  for any purpose other
than there intended use i.e. glassblowers filters for the prevalent
sodium emission lines.

From: dwilkins@orion.polaristel.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Didymium Glasses
Date: Mon, 05 Aug 1996 14:14:21 GMT

On 4 Aug 1996 22:12:44 GMT, dide@dgsys.com (Dave Ide) wrote:


>: I would not recommend these glasses for use  for any purpose other
>: than there intended use i.e. glassblowers filters for the prevalent
>: sodium emission lines.
>   
>   I got a pair to use for silver soldering.  They seem to do a slightly
>   better job of reducing the flux glare than the glasses sold by the
>   welding supply houses.  Is this hazardous to my eyes? I really do
>   hope to keep my eyes as long as I live..which is why I spent a lot
>   more money on the didymium glasses.      


I am a chemist who has done glass blowing and have not done any silver
soldering. The didymium in glasses provides a very narrow absorption
band for sodium emission lines. Normally one uses a hydrogen-oxygen
torch in glass blowing. The flame is almost colorless so the strong
emission from the heated glass is predominately sodium emission. The
emission from the torch used in silver soldering as well as the
emission from components in the flux will determine the safety of
using these glasses for silver soldering.

The manufacturer of the glasses should be able to provide safety data.

Subject: Re: Didymium Glasses
From: dwilkins@orion.polaristel.net (Don Wilkins)
Date: Aug 07 1996
Newsgroups: rec.crafts.metalworking

>OK, I give up. What is didymium? I know of Praesodymium, Neodymium and
>Dysprosium but I've never heard of the rare earth didymium.

Didymium is a mixture of neodymium and praseodymium. In practice it
probably has other rare earths present as well (with the exception of
cerium).  At one time the mixture was thought to be a distinct
element.

Didymium should be listed in any decent English dictionary.