Question

Which poetic technique does Robert Browning use in this excerpt from “My Last Duchess”?

"Of joy into the Duchess' cheek: perhaps
Frà Pandolf chanced to say "Her mantle laps
Over my lady's wrist too much," or "Paint
Must never hope to reproduce the faint
Half-flush that dies along her throat:" such stuff
Was courtesy, she thought, and cause enough
For calling up that spot of joy. She had
A heart—how shall I say?—too soon made glad,"