I often mix finishes to create custom colors or match existing finishes. Because oil finishes take longer to dry, the leftovers often need to be stored for a day or longer. I mix my stain in a plastic container with sloping sides. When I'm ready to store the leftovers, I lay a large piece of plastic wrap on top of the container. I use a second empty container of the same size to slowly push the plastic wrap down to where it lays on top of the unused finish to make an air-tight seal. When I'm ready to put on the second coat, I carefully remove the empty container and plastic wrap, stir and I'm ready to go.