Pyrex supplies running low ?

[John]

I've been following an interesting thread on the Cloudynights web site which raises severe doubts over the continuing availability of Pyrex glass suitable for astro scope mirrors because the main (only ?) manufacturer and patent holder, Corning, has stopped production now.

According to the posters in that thread, some of the premium scope producers in the USA have already announced major price rises to the scopes that use Pyrex mirrors to reflect their need to find and work another comparable glass type.

I know that some of the Skywatcher dobs use Pyrex mirrors wheras Orion Optics in the UK seem to use mostly Suprax glass from a German manufacturer. What other scopes could be affected by the dissapearance of Pyrex if and when it happens ?.

John

[FLO]

I think the benefit (low expansion) that Pyrex has over other glass types used in the manufacture of Newtonian mirrors is rather overstated.

I don't think its anything to be concerned about and suspect there are other more practical economic reasons for the price rises.

[LeoLion]

Hi , Must have missed that thread on Cloudy Nights (?) . The two materials I know as Pyrex (Corning) and Suprax ( Schott ) are as far as I know similar borosilicate glasses and with similar thermal properties . Oldham Optical have identified some recent supply problems within the UK for certain size borosilicate disks. This link http://www.oldham-optical.co.uk/Glass.htm carries those comments. I would doubt that the sole patentee was the Corning company . As I understand it Otto Schott (1851-1935 ) developed this glass to industrial maturity . Boron containg glass has been known of since the middle ages.

I know from surviving my many years of chemical laboratory work that borosilicate is much more thermally stable than soda glass ( not that you will subject your optics to anything like the same conditions ) !

There are , as well , the glass ceramics, such as Zerodur , Sitall and Cervit.I did have a visit to the Schott glassworks at Mainz (Germany) just a few years ago and seem to recall that Zerodur et al have some relationship to 'up market' ceramic kitchen worktops . The same visit we were told that there would be no more 8 metre mirrors from them as they had dismantled the large chamber furnaces used.

I would think that by now our Chinese scope suppliers will be sourcing their borosilicate mirror materials nearer home .

My own mirror making has only been with plate glass and my main scopes have borosilicate mirrors (bought in as part of complete scopes).

[rawhead]

Used to work for Newell, went up to Sunderland a few times, had a tour of the Pyrex factory. Didn't know they had stopped production....

[johninderby]

Pyrex is a brand name, although it has now become a generic term. Similar glasses for making telescope mirrors are available from other sources, so while Pyrex glass for telescopes is gone it's not really going to affect telescope mirror production.

With Pyrex or equivalent it is easier to obtain a smooth finish than with plate glass, which is why it has been so popular with mirror makers. The other advantage is that it cools down quicker (or reaches thermal equilibrium if you prefer) although once cooled there is no advantage over plate glass.

Actually the name Pyrex is still around, but it's now just the stuff used for cookware that's in production.

John

[Glasspusher]

I can only see one down side to the loss of pyrex, that is the price of borosilicate (low expansion) glass will increase. Inevitable I suppose given the ever increasing cost of energy! I have made many mirrors from pyrex and suprax and I have to say that my experience of pyrex is that it is inferior to suprax in terms of striae and homogeneity. Suprax is a better material to work with. Plate glass has it uses but is only made in thicknesses upto 25mm, a little thin for a large telescope mirror. Suprax is available upto 45mm at least. I believe the future of mirror blanks lies along the cellular route, the professionals discovered this years ago of course. Fusing thinner material to make a large stiff structure is what it's all about. The resulting blank reaches thermal equilibrium quickly and is relativily light. For most amateur sized telescopes monolithic blanks will be around in some form or other for quite some time to come.

The Chinese mirror maker, Hubble Optics (unfortunate name, perhaps something was lost in the translation!) of ebay fame produce a sandwich mirror consisting of two pieces of plate glass separted by many spacers. Reports suggest the blanks are well annealed with no print through (ie the effects of the spacers are not seen when testing). Perhaps this is the future?

I look forward with interest to see how the substrates used in larger amateur telescopes will develop. We could see 30 inch plus telescopes which are light enough to be practical.

Take Care

John

[barkis]

I made a 14" f6 mirror using plate glass. It took a beautiful polish.

Dob. mounted of course, it delivered some incredible views of Deep Sky objects. The blank came from a scrap yard, I could not believe it when I found a wooden crate with about 30 varying sizes in it. I bought a dozen for peanuts. Still have several left in a cupboard in the garage. Trouble is, they are all rough cut edges, and need ground off. Can't be bothered now I'm afraid.

Ron.

[The Warthog]

Actually the name Pyrex is still around, but it's now just the stuff used for cookware that's in production.

John

Oh, thank God! I was afraid the microwave and convenience foods may have made it unpopular in the kitchen. So, I don't have to run out and buy up baking pans?