Hempel Thinners No. 6 (also known as 851) is a paint thinner and brush cleaner specifically for use when spray painting Hempel two-pack polyurethane paints and Hempel Diamond Varnish.
It is important you only use the Thinners recommended for each application. Not doing so, or substituting other proprietary products, will result in an unsatisfactory finish. Also, with two-pack products, only thin the mixed product.