Sorry to take so long to reply to this.

There are two things that I think are helpful, in dealing with old compromised glass:

1) Apply oil to counter the white or off-color decay of glass. Any oil will help. However, my friend (anonymous) in the bead business SWEARS that the BEST oil is Regal Diamond Compound. This is made for oiling diamond trim-saws. It absorbs wonderfully well into old glass, and makes the colors stronger, and yet does not feel greasy afterwards. This is what I used on the early Venetian star-millefiori bead from the 16th C., that I showed a couple of weeks ago. It can be used sparingly (repeatedly), or you can fill a small jar and actually soak the beads in an oil bath.

2) For beads that have iridescence that you want to protect, there is a new product that is reversible and does the job. Unfortunately, I haven't committed the commercial name to memory. (But I can find out.) This stuff comes as white flakes (basically, it's resin), that you dissolve in acetone and apply to the bead. It dries totally clear, and sort of congeals or stabilizes the flakes of iridescent glass, so they won't break away from the surface and fall off. Yet, unlike other products, it does not counter the iridescent effect by "wetting" the glass. It's reversible by being soaked-off in acetone (of course).

In terms of what's available in the marketplace, related to ancient beads, I think a LOT of beads are recovered in good condition, and don't require much work for presentation. Those that are compromised, no doubt, do receive some work. However, most of the time, this is fairly apparent. What exactly they are doing or may be doing is almost unknown. (The folks who do this stuff are not going to tell anyone what it is they do!) A lot of it is (reasonably careful) abrasion. Basically the light sanding of the surface to scale-off discolored decay. I don't doubt that oil is used, perhaps liberally....

All of this is separate from the reverse situation, where fakers will take new beads, and dirty-them-up to look old. There are likewise a number of approaches or procedures to do this work too.

Jamey