Found out I had 4 hardware store masks in the garage (I thought I had only 1). They have been in the garage for several years and are a bit on the dingy dusty side. I currently have them soaking in a bucket of water with some oxi clean and a few drops of laundry detergent. I'll let them soak overnight and see what happens. If they do ok, I'll give them a good rinse and dry them in the sun tomorrow.