what does Broach symbolize in the An Ideal Husband?

Like the tapestry, the broach takes on multiple meanings through the course of the play. First, as a diamond snake, it symbolizes the evil woman—a woman who resembles a skin-shedding reptile in her duplicity.

The brooch also functions as an agent of vengeance. Ultimately revealed as a wedding gift Mrs. Cheveley stole in her youth, the brooch returns as evidence of a past crime, entrapping a woman who would manipulate past wrongs to her own advantage and wreck marriages. The "poetic justice" in her arrest is clear.

Finally, one might comment on the "duplicity" of the brooch. As Goring notes, the brooch is nothing less than a "wonderful"—or, in modern parlance, "fabulous"—ornament, a luxurious object that metamorphoses into a trap. As noted above, the dandy operates by trickery and artifice—not force—and always with style. In this sense, the brooch is the only "weapon" one can imagine the dandy putting to use, emblematizing his artfulness and guile.