What are some of the purest things in the world?
There are many substances employed in high technology that are extremely pure.
Some of the silicon used in very high performance semiconductors is pure to less than 1 part per trillion of impurities.
Some of the material in atomic weapons is similarly pure.
So also for the glass in the very best optics in the very best telescopes.
Science can now deliver some things to extreme levels of purity.