The famous "Green Rouge" polishing compound is used in the final stages of sharpening your knives to give them a great polished finish and to help remove any final burring when using your leather strop.
To use, wipe on your leather strop until you have a green layer on the surface and then strop as normal. This block can be very messy and so it is recommended you prepare your work area with some newspaper or a towel beforehand.
Note this block is 500g/19oz and is big enough to last a long time even with regular use.