Salt blued for sure.
It's well made. The blue quality is similar to Mauser M1930 (I don't have a S/42, so can only compare with M1930) -- metal polished, covered by near black salt blue.
Mauser's magic is not they could make a few nice guns. Many gun makers could make a few nice ones when the production volume is low, including Norinco. Mauser's magic was that they could make very high quality guns in large volume. Price was a little bit high, but not out of range. Interarms was merely $265 initially. Collectors "cooked" them to higher price, but extra money did not go to Mauser
