Sor Juana wrote this sonnet about her own portrait. The painting that flatters her — the «coloured deceit» of art — claims to defeat the years and save her from oblivion, but she takes it apart line by line: it is a vain artifice, a useless guard against fate.
The ending is one of the most famous chains in Spanish poetry: the portrait «is a corpse, is dust, is shadow, is nothing». In a single line she undoes the illusion of permanence a portrait promises, and turns the poem into a Baroque meditation on the vanity of everything that seems to hold off time.
The verse is kept in Spanish. Translating it in passing would replace the work with a paraphrase of it.