I'm sure that Spray Nine would take care of the mold, but be careful. Keep in mind that antlers are just bone, i.e. they're white. All the colouration that you see is from rubbing on bark, etc. to remove the velvet, as well as old, dried blood from when the velvet came off. If you clean them too well, they will start to look like they've been exposed to sun and weather for a few years, i.e. bleached and white. Bone is porous, so it would take some doing to overclean them, but it can definitely happen (don't ask how I know!).