I would definitely sash. Only I would use narrow sashing like maybe a strip of either black or white and cut the strips one and one half inches wide so it would be only one inch or one and one fourth with it ending up at three fourths inch. It will separate the blocks so you can enjoy each block on it's own and yet not be so white or black to detract from the beauty of the block. If you lay it out and stand back I think you'll see how nice that it can be.