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I say stag too for the reasons mentioned. The fissures on the ends of the scales on the larger knife and the semi trasluscent colour variations from some age and wear. One point if I may in response to an earlier post. Pores will only be seen in bone scales and not antler or synthetic. These pores indicate fine blood vessels which supply bone but not external antlers and horns. I think you did well acquiring the two for $30 IMO.
p.s. it may be some sort of European stag rather than Sambar.
I can always tell in person, by pic is much harder.
Agreed on this being bone, at least on the big knife. Cracks are something that won't likely occur on plastic knife handles. They can be damaged, sure, but it's more likely to have bone just crack on its own from exposure to air &/or light (not sure which is the culprit here -- other than the fact that it's no longer attached to the animal, of course).