Revive tired denim

I'd read sometime ago that you can 'revive' faded denim by washing it with a new dark denim item. I never had the combination of the two to test the theory until today. My faded denim is a much loved skirt that has, unfortunately, begun to see better days as the hem is starting to fray and it is seriously faded. But it's still perfect for hiking, camping, cleaning the house, gardening, etc. and I wanted to freshen up the colour. Today, I tossed it into the washer with a new dark denim skirt I bought recently. A half hour later, my faded skirt was about two shades darker!

The second part to this story is to, of course, wash new dark denim separately as it obviously does run!