Butter London Nail Foundation Flawless Base coat This Nail Foundation Flawless base coat from Butter London is a treatment that will hide and smooth tiny ridges and imperfections in the nail. It is like cover-up, or foundation make-up for the nail. It leaves a silky, matte finish when used alone. This makes it an excellent product for MEN who want an invisible, but immaculate manicure. When used as basecoat, it provides a beautiful, smooth surface on which to paint.