I feel like a good bit of the joint discomfort that comes with scrimshawing is from how difficult it can be to manage the horn will working on it. You end up losing a lot of efficiency from your scribe hand and are forced to overwork it. I was fortunate enough to sit by a journeyman horner at that class I went to and he let me borrow this rice bag he made, he brought in extras for people to try out. It was about as big as whatever you'd imagine you'd need to rest a horn on and it was made from chamois leather (natural shammy cloth like what you'd dry your car with), the tackier side out. You could put that chamois rice bag over a vice or, in my case, this bag of rice and beans I brought in and the horn would conform perfectly to it and it would grip it firm. Wouldn't move while you were working on it. I'm about to stitch one up for myself.