Lately I've also been economising by painting on top of paintings that have failed. I scrape the surface to get rid of any texture and then wipe with some liquin. I find this gives a better surface than a new canvas board, also some of the under painting can be left to show through to give a more richer effect. Underneath this painting is one I did of wildflowers last year, at the time it looked ok but only when you look back can you see the errors. I am my own worst critic and I think most artists are but with experience you just know when a painting has failed or succeeded in portraying what you want.
Oil on canvas board 7"x5"