| Quote #1
Sir, ’twas not
The Duke is offended that the Duchess would take pleasure in anything other than him. Notice that the way she shows her pleasure is involuntary, (i.e., a blush counts as showing pleasure), but the Duke describes it as though it were a stain or taint, a "spot of joy."
| Quote #2
The Duke’s jealous fantasies are very elaborate – he’s imagined in detail the kind of compliments that the painter might have paid to the Duchess, and the coy way that she might have responded. It’s important to remember that, as far as we know, this could all be in his head. There’s no evidence in the poem that the painter said these things or that the Duchess blushed in response.
| Quote #3
The Duke seems to believe that the Duchess chooses to blush or react to compliments and gifts. He describes her as "calling up" her blushes, instead of experiencing them as an involuntary reaction. As readers, we know that she probably isn’t blushing intentionally, and the Duke’s jealousy is illogical.