~~~ ivory chips for cracks is in the actual groove (ring or rings) recess by holding the chip up to a light and wiggling it at different angles to notice if light passes through. If ivory turners knew back then what we know today, they probably would not have placed those rings in the same exact position from the edge on both sides of the chip; making that depression the weakest area of the chips... especially when in heavy use being tossed around against and upon other chips. This ringed area is often overlooked while inspecting chips.

I once bought a bunch of remnants from a single set that had so many holes in them, that they were 'plugged' with actual ivory (I guess to prevent further cracking). You can sometimes see those plugs on ivory pool balls as well.