I would prewash the new by throwing into a mesh laundry bag. and throw some color catchers in with them. The older one's maybe hand wash. I got some vintage squares and washed in a mesh bag on a delicate cycle in warm water. I threw a color catcher in the mix just in case. These squares were a light-medium green and yellow. They all bled. Was glad I washed them. I tossed them into the dryer on tumble low.