A woman's face with nature's own hand painted,
Hast thou, the master mistress of my passion;
A woman's gentle heart, but not acquainted
With shifting change, as is false women's fashion:
Nature is depicted as an artist painting, or creating, the young man’s face. The point is that his face is as beautiful as that of a woman, with an implication that is better. As the following lines will show, it is without the “defects” associated with female beauty. Implied is the idea that his beauty is natural and unspoilt, not disfigured by cosmetics which, at the time, contained poisons that damaged young skin. 

Sonnet 20