We've been doing this for years, but I've never used a mason jar to do it. I just take a bottle of the cheapest vodka (the stuff we used to get in Virginia came in a plastic bottle), put about a half-dozen whole vanilla beans in (depending on the size of the bottle), and leave it alone until it looks the right color. Sometimes, when the old bottle is used up, I'll transfer the vanilla beans to the next bottle (along with some new ones, of course). You sort of have to plan ahead, and start the next batch in time to have it ready when the first batch is used up.
One other thing. After all the extract is used up, don't throw the beans away without squeezing out every drop of the remaining liquid in them. It's the most potent part of the whole process, don't let it go to waste!