Most photographers of a certain age began their journey with black and white film. We learned the basics of exposure and development and then marveled to see the tones emerge as we rocked a tray of chemistry with our first print. For some, this magic never abated, and they continued to hone their photographic skill in shades of gray. Two recently published books revel in subtle monochrome tonality: Agnieszka Sosnowska’s “För” and Regina DeLuise’s “The Hands of My Friends.” Their pensive and reverent explorations inspire renewed gratitude for photography’s enduring spectrum of grayscale.