"A Face" begins with a daydream. The poem's speaker longs for a painting that never existed: an Italian Renaissance portrait of a woman whose beauty he finds irresistible.
He's clearly a guy who knows something about Italian art. He desires, not just any Old Master, but a work in the style of the "Tuscan's early art"—that is, in the style of a master from old Florence, the greatest city-state in Tuscany and the nerve center of the Renaissance. He may even be thinking of one Tuscan in particular: Giotto, whose unprecedentedly naturalistic religious paintings were often said to have marked the dawn of the Renaissance. Giotto frequently used the "background of pale gold" the speaker desires, a fine layer of gilding meant to gleam mysteriously by church candlelight.
The imagery of that pale gold background suggests that the speaker sees the lady's “little head” as something almost sacred. Her beauty, he specifies, should be framed like a venerated saint’s. For that matter, her face is worthy of depiction by an immortal artist, a long-dead great whose work lives on. The speaker romanticizes not just this lady’s beauty, but the art of the Renaissance, an era that many 19th-century European thinkers (like this speaker) admired.
The tone here isn't pure awe and delight, however. Pay careful attention to the enjambment in the first lines:
If one could have that little head of hers
Painted upon a background of pale gold,
For a split second, the line break makes it sound as if the speaker wants to have this lady's head in a more Henry VIII sort of way—a way that might involve not a paintbrush, but an axe. Even the simple word "have" feels a little uneasy in that light. The speaker longs not just for a record of this lady's beauty, but a way to possess her beauty. And the rather condescending tone of "that little head of hers" suggests that he might not have thought too much about what the lady herself might feel. The dear, she shouldn’t worry her pretty little head about anything.
All in all, these first lines suggest that this erudite, aesthetically sensitive speaker loves this lady's beauty, not the lady herself. To him, in fact, her feelings, her independence, even her identity might not matter much: she's "A Face," not a person. As this dramatic monologue develops, this speaker will subtly, sinisterly join Browning's catalogue of dangerous men, admirers who want to possess and control what they claim they love.
The speaker will expound on his imagined, ideal painting of this lady’s face in 22 lines of iambic pentameter—that is, lines of five iambs, metrical feet with a da-DUM rhythm, as in "If one | could have | that lit- | tle head | of hers." This form makes him sound as if he’s delivering a Shakespearean soliloquy—a suitably Renaissance-y tone for a man with Renaissance-y tastes.