Wear gloves when gathering used velveteens.
Some labs collect used velveteens in an empty bucket.
The dark color of the velveteens is necessary for seeing your cream-colored yeast prints. If the container is kept on the floor be especially wary of lab tools that may have fallen in, e.g., pasteur pipets, razor blades, toothpicks. They may be hung up to dry, or dried in a laundry dryer. The dryer is better because it fluffs up the velveteen and raises the nap. Otherwise, use as little detergent as possible.