Wiss scales.

If it has little black "specs" or almost like pinholes that you can see as it looks like in the photo, then it is bone. That is proof of the remnants of the Haversian system (blood vessels running through the bone I think). If the black dots aren't there, then it may be Ivory, but it could still be tough to tell. Bill Ellis says that most of the time it isn't and he has seen some examples of celluloid where you can't tell the difference. I got a razor recently that I think has genuine Ivory scales. There is a test which I have not yet done. If you heat a pin (don't know how hot- I assume very) and try to touch it to the scales, if is plastic material the pin will melt into the scales. If it is Ivory or other natural material, it won't.