Re: [ATM] Pictures

[Anthony Stillman <atmer@flash.net>]

Speculum Metal Mirrors

advantages
-no need to aluminize
-can test with a faint light sources
-the tube balances close to the mirror
-faster than glass thermal equilibration
-something different (bragging rights)

the down side
-low reflectivity ~60 percent
-temporarily blindness when testing with a bright light source
-the mirror is really heavy
-huge thermal expansion ratio
-hard to obtain a decent polish


I alloyed the metal, 110 grams at a time, from tin (most given to me by
Richard Schwartz) and scrap copper, using an oxy-acetylene torch.

Annealing.  The 62mm mirror (sixth casting) was not annealed.  The second
90mm blank, the one that broke while roughing out the curve, was.  The
metal is very brittle and somewhat weak.

I haven't done enough experimentation with rapid solidification to effect
grain size.  The last three blanks were frozen slowly while the torch was
played over their faces.  In comparison to my early efforts these blanks
are practically free of porosity.  I think this is a far more significant
issue than grain size in obtaining a good figure.

Why bother?  I like to try different things and, reviving obsolete
technology using modern techniques appeals to my idiosyncratic iconoclasm.

Next post I'll report my successes.


Anthony


cives censent, servi non facent
Citizens vote, slaves don't.

The Latin "v" is pronounced as an English "w."  The "i" sounds like a long
"e."  The "c" is always hard.  And yes, I think ATM's are far more likely
to vote than not.  Saddly, not everyone is an ATM.






>At the attached addresses are images of my most recent speculum metal
>mirror failures.
>
>First 90 mm casting.   The casting investment vented steam through the
>liquid metal.  Like visiting "Yellow Stone", on Io.  One of these vents,
>split in two,  is visible on the right two pieces.
><http://www.atmlist.net/contrib/atmer-at-flash-dot-net/Vented.jpg>
>
>Second 90mm blank.  Broken while using an every so slightly unbalanced 220
>grit grinding wheel to smooth the curve roughed in by a balanced 100 grit
>grinding wheel.
><http://www.atmlist.net/contrib/atmer-at-flash-dot-net/Broken.jpg>
>
>Close up of the second blank's broken face.
><http://www.atmlist.net/contrib/atmer-at-flash-dot-net/CloseUp.jpg>
>
>
>
>Anthony
>
>
>cives censent, servi non facent
>
>
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>ATM mailing list http://www.atmlist.net/



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