Hey Superdav. Yeah, I think I'll just leave the sinew bare. I had a snake skin, but I used it on a different bow, so I don't know what I would use to cover it. The method I used was the one "rediscovered by Keith Shannon" where you build a pit fire using cinder blocks and charcoal briquets for a nice controlled fire and then lay the bow over the fire clamped to a form. At this stage, I had just shaped the bow out and barely even done a floor tiller. I used a form that curved backset into the whole length of the bow. You can see a picture of the bow unstrung here. Notice how it still has a slight curve towards the back. There were originally about 2 and a half inches of backset, but most pulled out because I'm not an expert on tillering to preserve that.
Anyway. After I put it over the fire, I checked it every 15 minutes. The bow was elevated about 14 inches above the coals. There was no flame; the coals were just glowing and making a lot of heat. After about 30 minutes, there was already quite a bit of color. I left it there for almost 3 hours trying to maintain a constant heat, but going slowly to make sure not to over do it. I did scorch it a little in a couple places. That's part of the reason I wanted the sinew for insurance, but I think it probably could have survived without it because of the toughness of hickory.
Here's a picture of what it looked like when it was finished before I took more wood off in the tillering stage.
If you're interested in making one of these, you should check out the DVD made by Keith Shannon, Thad Beckum and Billy Burger. I think there's also a way you can order fire hardened blanks to shape out if you want to make one, but don't have access to a fire pit.