There are a bunch od methods you can do for velvet preservation . Personally I have injected them using velvet tan, and have done an actual Tanning bath using alum tan to preserve velvet. There are many other methods that have been used and have worked through out the years . I know there is guys using turpentne, some potent jet fuel , white gass,formaldahyde etc. I can say I had 2 caribou that were done in the jet fuel, one turned out OK with some slippage and the other was half preserved and half rotted as all the blood was left in the antlers. You do need to drain the blood out of the antlers or spoilage may occure. You can inject every main vein and poke small holes in the tips of the antlers and you should get them to drain by replacing the blood with some type of preservative of your choice. Key is to get wahtever you use in the veins to replace the blood and them submerge . I could go on for pages on this subject with all the different ways of doing this process.