By far the best way (and the only really reliable way) is to get the antlers in a freezer ASAP and get the velvet freeze dried. Antlers in velvet contain blood. Remember, velvet is live flesh. Of course the less "mature" the antlers are the more blood and the greater difficulty preserving velvet. If you drill a small hole in the base you'll be surprised at the blood that comes out. A good rule of thumb is that Velvet will "spoil" nearly as fast as meat. Over time there have been various methods used to preserve natural velvet. Including velvet tan (as mentioned), injecting formaldehyde, etc... There are many variables (as mentioned - weather, maturity of antlers, etc..) but even best case scenario velvet preservation is iffy. Another option is to strip them and have your taxidermist apply artificial velvet. My Taxi shipped a Caribou rack of mine to Research Manikins in Washington and they did an excellent Job on the artificial velvet. I also have a B.C. Moose rack in full velvet that I was able to keep really cold and have freeze dried. That was 20 years ago and the velvet is still perfect. Hope this helps. Good luck. Chip