It's a white chalky powder you mix with water to a runny paste (experience gives the right consistency) that you then rubbed onto shiny areas of the boat/yacht. This could be left on all through storage time or washed off twenty minutes later. It did a very good job of removing yellow staining and left the hull clean and ready for polish. Oxalic acid was one ingredient I believe. V good stuff. £12 for 500mlish and lasted 2 years
Instructions are a bit different to how a lot of people used to use Wipe-Out though - may have to do test piece before leaving on all winter to wash off in Spring!