Paint thinner and nail polish remover have completely different properties, so the latter won't replace the former as effectively.  However, it can be a cheap alternative to thin out the paint. Acetone bonds quite well with oil-based paints, so it can be used for dilution.  To use nail polish remover as a paint thinner, follow these steps:  1. Stir the paint thoroughly with a wooden stick or disposable mixer.  2. For every gallon of paint, add about an ounce or an ounce a half of nail polish remover into the container.  3. Mix the solution for about 30 seconds.  4. Test the thickness on a disposable surface. If the mixture isn't thin enough, add up to a maximum of 12 ounces per single gallon of paint.