OPI Natural Nail Base Coat OPI Natural Nail Base Coat is a nail lacquer designed to keep the strength, colour, and integrity of your natural nails ever after the most intense and repeated painting. Natural Nail Base Coat is a base coat painted onto your nails to prevent paint from seeping through your nails and staining them permanently. As with any OPI base coat, Natural Nail Base Coat is formulated for smoother paint application and longer lasting paint treatment. Use Simply apply Natural Nail Base Coat before painting with another OPI nail polish and finishing with a top coat.