Best Glass for UV Contact Printing

I seem to remember from my college days that regular glass filters UV. What's the best glass for UV contact printing in a print frame.

Is possible UV filtration the only issue one deals with in selecting a glass? Can Newton rings be a problem? I'm going to be printing with digital negatives.

Gosh, I just saw a pre-existing thread ON THE SAME PAGE as my thread. I obviously missed it. Apparently, there's a Water White glass that does a good job at passing UV light. But, I don't see too much mention of whether or not Newton rings can be a problem, or how to prevent it.

I just use regular old picture frame glass. It cost more if you want the UV Protective layer on it...so just dont get that.