I think after you send the gun to Mal H ( mods first-right?) send the gun to me...we'll get back to you.
[ work with me here Mal...I'm trying.
OK, in the pic's it appears to be pearl all right. Follow me on this if you will. If you go to a Jewelry store and look at a "loose" mobe',[mabe' ]pearl (unset, not in a mounting) you will note similarites to your pic.
The skin ( nacre') is 'shaved' removed from the oyster. In this state it is very thin and weak. Thickness- if you will -is determined by age of pearl in oyster. Ok they then "fill" this hollow nacre' with putty type substance for strength and stability. Usually a off-white putty color. Often times, not always a transparent coat of hardener is applied over the putty substance only ( kinda like a clear coat). In Jewelry, this color ( off white/gray.kahki) is more appealing to the various mountings...gold ( 14K and 18k yellow and white) and Platinum...just looks more appealing.
On the Gray, "Black" ...various other colors of pearls they use a darker putty, which is what your pic/grips show. Being as these were designed as grips and the back would never show, they used the dark putty. I really never noticed a difference in the strenght of the two putty(s) btw.
The putty is just allowed to dry and then shaped, smoothed for cosmetic appeal.
Nice looking grips!
Drilling pearls is tricky ( I don't see grip screw holes in yours). Pearls will split/chip/break easy. Getting a start on a smooth slick surface takes a knack too .. Drill will skate all over the place...you don't want that. They do make a special "pearl drill bit" for , naturally, drilling pearls. Pearls will dull a bit--quick, the heat from drilling will discolor and break the pearl. The "twist drill" can work...but...this is where using a very low speed on a Foredom Flexshaft and having a good foot pedal rheostat really really is needed. Having the "touch" and experience is a bonus. Start small, go slow, keep changing to larger sizes, and be patient. Not a bad idea to stop, walk away, then go at it again. I can't stress enough the importance of only using the Foredom Flexshaft in the variabe mode. I made my point 20 yrs ago with my buddy whom had his set on "high" as we call it. I moved that cabe to the other 'shaft setting and he never regretted it and never used "high speed" only again. Applicable to not only pearls btw.