In the medium’s early years, photographers seeking clients often used a bleak tagline: “Secure the shadow, ere the substance fade.” Which is to say, capture your likeness before it vanishes. The portraits in this show were made using the whole-plate format, a large and costly daguerreotype measuring 8.5 by 6.5 inches. Among them are striking likenesses of U.S. senators Daniel Webster and John C. Calhoun—defying time’s erasure. —Elena Clavarino