Bone for tone, goes the saying (well, in certain circles, at least).
And it's right. Bone's my favourite substance for nuts and acoustic saddles. It looks great, lasts well and works nicely. And, of course, the tone's all there.
Except when it's not.
The problem is that bone's a natural substance. Sometimes there are bits that are less hard or dense than others and it's important to keep an eye out for this when you're making a nut or saddle.
The less dense area of the piece in the photo is easy to see. A hefty semi-circle that allows more light though gives it away. It's not always so obvious and it's not always so big. If I'd cut a string slot in this part, there's a good chance that string would have a different tone to the others. The slot would certainly have worn more quickly than the others, too.
By the way, bone (especially unbleached bone) has many small differences in colour here and there. If you spot small specks and streaks in your own nut, it doesn't necessarily mean you've anything to worry about. When you're making a nut or saddle, though, it's not a bad idea to examine the blank bone first.
This one? This one went in the bin.