Pure gold does not tarnish. The "grade" depends on the amount of alloy metals like silver, copper, nickel, zinc mixed with the gold which do tarnish. 10 karat gold, for instance, is only .4167 % gold, so tarnishing of the alloys is quick and obvious. 18K gold is 75% pure gold and the alloys will tarnish more slowly over time. In neither case does the gold tarnish.
Perhaps tarnish is incorrect...let’s go with patina.