In our applications so far, this typically means coating the INSIDE of various size vessels. Such a Teflon coating can do many things, such as reducing the absorbtion of metals from the pyrex into the chemical being processed, or prevent/slow down the chemical eating its way out of the
pyrex vessel. . .

We have successfully coated the inside of moderate sized vessels, such as 50 liter flasks. We have also coated the inside of some more complicated items, such as a condensor - where we coated the coils and the inside of the cylinder.

Several problems occur when coating pyrex with Teflon. The primary one is ADHESION. Getting teflon to stick to anything is a challenge. To slippery glass even more so! So, off to research the problem. And we found a dozen chemicals that people claimed would etch pyrex. None worked. But we figured out a special process. . . and can now etch pyrex!

By the way, etching normal soda glass is trivial. But since no one would want to coat a soda glass container with Teflon. . .

A second problem is that all forms of PFA and PTFE are made to be applied over a primer, which has been applied over an etched surface. Close examination of the ingredient lists shows that all of the primers contain heavy concentrations of heavy metals. So, if you are trying to
keep a tiny bit of boron or some such out of your product, and you accidently scratch the Teflon coating, exposing the primer. . . you now have heavy metal soup.

We have had excellent success with avoiding these heavy metal primers. Which can often result in a translucent, almost transparent surface! (with excellent adhesion)

PFA and PTFE are fascinating coatings, with interesting properties that are not in the literature,
and application notes/requirements that are - well, fascinating. And we may now be some of the
world experts in their application!