Do glass shelves affect sound Quality?

The answer is yes, but exactly how much and whether it's bad is debatable. Glass has a bad reputation among some audiophiles. You'll find comments about ringing and glass adding a hardness to the sound of components. In the past I've used glass and didn't have any problems, but I was using fairly thick 1/2 inch slabs. If you want to experiment I would suggest starting with rubber or cork type footers to see if you notice an improvements in sound quality.

Agree with Onhwy61. I've always avoided glass but how much it deteriorates the sound would be hard to judge.

All my racks have glass shelving clamped at the sides in 'U' shaped slots.
I added packing to the slots, (besides the nylon clamping setscrews)
Then most of my stuff is on butyl rubber feet (under the stock feet) and/or clamped between the shelves above and below.
I have no problems with using these racks.
The ywere cheap, pretty, and the frame was sand fillable. Which I did.
They are never going to be replaced.
Naturally they are an odd brand i never heard of before, and have never seen in years since i bought the three I use.

Thanks for your responses.

I inquired about Herbies Audio Lab and they suggest using a set of tenderfoot under each component plus a supersonic stabilizer on each component. Has anyone used these products and will they be effective on glass?