What metaphors are in my last duchess and what is the message they convey?

Robert Browning's "My Last Duchess" does not rely heavily on metaphors. It is rather a monologue delivered by the speaker describing a painting of his wife and his wife as a person when she was still living. The painting can be said to symbolize the wife, the last duchess. There are a few metaphors sprinkled throughout the poem, though, as the speaker paints a verbal portrait of his former wife.

When the speaker says in lines 1-2 "That’s my last Duchess painted on the wall, / Looking as if she were alive," his choice of words could be considered metaphorical. The duchess herself is not literally on the wall; rather, this is a painting or a likeness of her, which stands in for her throughout the poem. One of the few metaphors in the poem is the "spot of joy" referenced by the speaker. The speaker suggests that most people wonder what exactly makes his lady smile and appear happy in the painting.

impartial means: treating all rivals or disputants equally; fair and just.

i would say that impartial is agreeing with something, because impartial means to treat your rivals, arguments, and reasoning equally and fair. so if you rival says something, agreeing on it means you did the impartial.