Here is a bow screw's button that had three missing mother of perl pieces. The unusual thing about this button is that each piece was seperated with a small piece of ebony. A couple of those were also missing.
The easiest way to repair this was to find a matching mother of perl slide. Then cut off small pieces that were the same width as the facits of the button. Then just hand fit them.
IMG 20160304 162201 IMG 20160304 170213 IMG 20160305 175916