(You can vessel a gem more than once, if you don't fill it up completely. For example if you start casting Vessel at 7.5 favor, you will fill it up with approximately
2.5 favor (gain 5 favor on use), then when you use it the gem will lose around 3-4QL and can be revesseled and reused until it disappears after reaching below 0QL)
A Priest can not use a linked priest's favor when vesseling. (You use your own, but not the link'ed priests)