For many long years, we were told the rumor that glass is acidic and should not touch the fabric or threads. THREE organic chemists have verified for me that glass is neutral. If anything, it may be INSIGNIFICANTLY very slightly alkaline, the opposite of acidic!
However, if you live in a highly humid or damp climate, you may want the framer to use frame "spacers" to make a tiny space between the glass and your project to prevent condensation, which can cause mold or mildew to grow on the project. This will ruin it. The space allows it to not accumulate the condensation.
Another consideration is fading. Needlework should be framed with museum glass or UV glass, which will prevent sunlight from fading the floss/threads/fabric. If you display it in a hallway or a room where it won't get much sun. Have you noticed that most museums do not have any windows in areas where paintings are displayed? Fading is why!
Hope that this answers your question. I am not an employee of ECS, just an old stitcher on this chat group.
I saw your question and wanted to share this info.