In what chapter of The Scarlet Letter is Dimmesdale's mark first revealed?

Dimmesdale's mark is first revealed in the novel's penultimate chapter, "The Revelation" (Chapter 23). He calls Hester and Pearl to him, just after he has delivered the Election Day sermon, and though Roger Chillingworth tries to stop it, Dimmesdale asks Hester to help him up onto the scaffold. He says to the disbelieving crowd, "'behold me here, the one sinner of the world! At last! — at last! — I stand upon the the spot...

Dimmesdale's mark is first revealed in the novel's penultimate chapter, "The Revelation" (Chapter 23). He calls Hester and Pearl to him, just after he has delivered the Election Day sermon, and though Roger Chillingworth tries to stop it, Dimmesdale asks Hester to help him up onto the scaffold. He says to the disbelieving crowd, "'behold me here, the one sinner of the world! At last! — at last! — I stand upon the the spot where, seven years since, I should have stood.'" First, he confesses his guilt and his connection to this woman and her child. He asks them to look again at Hester's scarlet letter and claims that it is only a shadow of the one he carries on his own chest, of the one that is burned into his own heart.

Then, "With a convulsive motion, he tore away the ministerial band from his breast. It was revealed! [....] For an instant, the gaze of the horror-stricken multitude was concentrated on the ghastly miracle." It is at this moment that Dimmesdale reveals the mark on his own breast, and Chillingworth realizes that the minister has "escaped" him. Pearl kisses Dimmesdale, and "A spell was broken."

Later, in the last chapter, "Conclusion," the narrator says that "Most of the spectators testified to having seen, on the breast of the unhappy minister, a SCARLET LETTER — the very semblance of that worn by Hester Prynne — imprinted in the flesh." They speculate that he tortured himself by putting it there, perhaps with a blade, perhaps with a brand, but neither we—nor they—know for sure.