I started using Future Floor Polish last fall. I mix 1 part Future, 4 parts water, and ink to make a wash. I have also used paint to supply the pigment, but the ink provides a smoother result.
I used the wash on my 40K Necrons. I "painted" them with a spray on chrome, and then washed them with a black wash to protect the chrome and define the areas. (In my first attempt, I destroyed 6 months of work when I did not cover the chrome before spraying on the sealer. Six months of work destroyed in 5 minutes. I was heartbroken for days.) I then added paint over the Future for details.
I started an experiment on some High Elf Swordmasters, because the High Elf scale mail drove me nuts when I painted it. The results are encouraging, but I used a wash based on paint rather than ink. I haven't created a new wash with ink yet.
It occurs to me that I used my purple Future wash on my daemons for my Daemon army. See the Warmaster Tale of Painters. See especially "The Watcher in the Sky". All the Daemon horde units were washed with a wash to bring put the details.