That looks like a bone handle. Something I forgot - when Ivory cracks it will (unless really brutalised) crack along the length of the grain - bone doesn't as its structure is completely different. Bone cracks tend to either radiate from the pin or wander of jaggedly. Point taken about using thick ivory but those are, after all, custom scales (I'd love to see 'em!). Old ivory is generally very thin and cracks easily especially when it's a good age. Anyway, it gives the razor character!