Here are the reasons I no longer use glass either for Claybord or paper based Scratch work.
1. I prefer it for cost, Weight and pain in the ass mounting, cutting matte and glass , etc, etc etc. Also glass should never be touching the Board surface so a matter or Frame space edge needs to be used. Do not forget reflection on flat Back surface. You look at the surface and you see yourself along with the subject. Non - Refective glass, dull, dull and dull!
2. My clients and gallery don,t like glass either.
3. As far as protection, I and the gallery make it clear as to how the board is covered and protective and that Sprays and Clear painted coatings can and do protect from static air condtions but do have limited protection by physical contact. They must buy and preserve under those conditions.
However, I have always let my clients know that from the day they buy an original of mine I will do my best to correct and make presentable any thing that can be repaired the best I can at no charge as long as I am available. They like that and I have repaired about a dozen pictures in my years doing Scratchboard. Keep those Micron Archival ink pens in good condition. They are a god send for many a repair and when you coughed while scratching.
As far as colored frames, A Black, Grey, White frame look great on B&W Scratchboard. Any color in the Pic, the door is open for color or type do to subject matter. Regards