Hi
As phomer pointed out, you need 2 types of glass to make an achromat, or ED lens, that have different refractive indices. There was a book published by Willmann-Bell who have recently ceased publishing, unfortunately.
https://www.willbell.com/tm/refractor-telescope.htm
I don't think that Pyrex was a suitable glass for one element of a refractor objective. Much easier to buy an objective if you wanted to make a refractor but the price of achros' these days make it more worthwhile buying a complete ota. Unless of course you are like me and just like making your own anyway with commercially available lens and other bits.