I recently bought some tung oil (Formbys) and some Danish oil (Watco) in 1 quart cans. I put some of each in 1/2 cup glass containers for convenience. The Danish oil is like new but the tung oil in the glass container has turned to wax. Also, I use Minwax Polyurethane, and have to buy a new can about every four months. It gets so thick it can't be applied. After five or six months it turns so solid I can't push a screwdriver into it. Whatsup?