Try the Picro - thionin method that you will find in any good text-book.  
A GOOD sample of thionin is essential for the best results, but you will 
probably get along with a batch that is a little less than perfect.
Strongly recommend a BSC (Biologic Stains Commission) approved 
batch.

Silver staining is also surprisingly good, if a bit more of a "fiddle" than 
picro-thionin.  Almost any method will work so try the simplest or that 
you are most familiar with

Fixation should not matter - except that it should have been used.
Even so, I have stained dinosaur bone and I do not believe formalin 
had been invented when that poor chap died.
Russ
Russ Allison, 
Dental School
Cardiff
Wales