Ok, here's a bit of a weird one. I've put two bones in a hydrogen peroxide mix (50% water and 50% 6%concentration, hydrogen peroxide) and my small vertebrae was fine, the other started to go a lilac colour. The other bone (the one that started to go lilac in places) is a rather long, hollow bone. I found both of these bones about a month ago. Both were washed up very clean, on the beach. I gave them both a good three washes in tap water. I'm not bothered by this odd change of colour (which has already begun to fade). Yet I'm very curious as to how it got there. A reaction with any leftover sea salt? Contamination in the solution? To be honest, I really don't know... And that bugs me, a lot. So, any theories or suggestions folks?