Re: ATM 11.5" mystery glass

["PETER JOHN SMITH" <pjifl@bigpond.com>]

> Last night I started rough-grinding a piece of glass "inherited" from the
WW2-era
> stocks of the old National Institute of Standards. It's 11.5" in
diameter, 2"
> thick, and it has some interesting data written on the side with
grease-pencil and
> engraved into one side of the glass.
> 
> Anybody care to decipher them? They are written in a European hand (1's
with a
> pronounced upward zig, crossed 7's, etc)
> 
> Here goes:
> 
> BaF4 - Z4135 Opt 7702 / Pos 2/38
> 
> I suspect the BaF4 means a type of glass containing Barium Fluoride, and
the 2/38
> may mean February 1938, but the rest I really cannot guess at.
> 


BaF4 is a relatively unusual light flint glass. 

It could certainly be used as the flint in a refractor.  In fact I would
guess it could be used in something approaching an APO design.

Have no time at the moment to investigate further.

BUT UNDER NO CIRCUMSTANCES SHOULD YOU WASTE A VALUABLE PIECE SUCH AS THIS
ON A REFLECTOR.

Peter Smith.