Hello,
Saw this and couldn't resist the thought of some funky black telescope glass.
The prices for the pre-curved blanks are surprisingly good though and the BVC is better* than Pyrex over 400mm for acclimation.
The blanks have between 3-5 F/l up to 20", after that its mostly only two options for the focal length up to 30".
They are thin light weight mirror blanks!
It is not a secured site however... so proceed at your own risk which is a little sad for this day and age.
http://www.bvctek.ca/thin-pre-curved-mirror-blanks.html
*"We have been passed test figures from the Canadian company showing a range of 2.56 -2.64PPM/Deg C, which supports their claims. Note even the worst of the figures quoted, - 2.8PPM/Deg C, - is still lower than Pyrex." from Astrofox Astronomical Instruments website.
**Easier better cheaper = Easier this is soft glass, a lot softer than soda lime and the black colour apparently helps with pit detection. Better = cools down even faster than Pyrex and sandwich is very light you can get to 24" before you break 10 kilo. Cheaper well certainly compared to some pre-curved large blanks I've looked at....
And a page about working with the glass with all the makers spin, but looks like you will need to smooth the backs.
http://www.bvctek.ca/bvc-glass.html