"Listen, then, Jane Eyre, to your sentence: to-morrow, place the glass before you, and draw in chalk your own picture, faithfully; without softening one defect: omit no harsh line, smooth away no displeasing irregularity; write under it, 'Portrait of a Governess, disconnected, poor, and plain.'
"Afterwards, take a piece of smooth ivory—you have one prepared in your drawing-box: take your pallette, mix your freshest, finest, clearest tints; choose your most delicate camel-hair pencils; delineate carefully the loveliest face you can imagine; paint it in your softest shades and sweetest hues, according to the description given by Mrs. Fairfax of Blanche Ingram: remember the raven ringlets, the oriental eye;—what! you revert to Mr. Rochester as a model! Order! No snivel!—no sentiment!—no regret! I will endure only sense and resolution. Recall the august yet harmonious lineaments, the Grecian neck and bust: let the round and dazzling arm be visible, and the delicate hand; omit neither diamond ring nor gold bracelet; portray faithfully the attire, aërial lace and glistening satin, graceful scarf and golden rose: call it 'Blanche, an accomplished lady of rank.'
"Whenever, in future, you should chance to fancy Mr. Rochester thinks well of you, take out these two picture and compare them: say, 'Mr. Rochester might probably win that noble lady’s love, if he chose to strive for it; is it likely he would waste a serious thought on this indigent and insignificant plebeian?'" (2.1.72-74)
Notice that the portrait Jane draws of Blanche is completely imaginary; she hasn’t seen or met Blanche yet, although we already know that Jane’s drawings and paintings sometimes have an eerie way of looking just like real places and people that she’s never seen.
These portraits probably tell us more about the contrast between who Jane is and who she wishes she could be than about the real contrast between Jane and Blanche. It’s like feeling a bit depressed, having low self-esteem, and comparing yourself to airbrushed pictures of Zoë Kravitz.