Re: [ATM] Glass Blank Question

["Bob May" <bobmay@nethere.com>]

Jason, since you don't know what the glass type is, it will be of
no use for a refracting element in a lens unless you are
interested in doing a single element refractor.  That leaves the
only possibility of making a reflector with the glass.
As far as glass for a reflector, glass is glass.  Some is harder
than others and some is more brittle than others but that only
matters for the mechanical handling of the glass.  Pyrex is one
of the harder glasses (only the 0 temp coefficient glasses are
harder glasses that are normally used for mirrors) and anything
else will be a quicker grind and polish.
The appearance of a tempered piece of glass will indeed be like
that of the tempered windows of a car.  I'll also note that I
often use the glancing reflection of the light off of a car's
window (no relation of whether the window is tempered or not but
rather that a glancing reflection is highly polarized) and a set
of polarized sunglasses to do my testing for temper in a piece of
glass.  You don't need for the light to come directly from the
source as a slight angle as you would see from a piece of glass
being held in front of you with the light reflection in the
center of the glass will show very nicely the phase changes in
the light.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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