PROVINCETOWN — The Prussian blue in cyanotypes feels like the stuff of dreams and memories. The color itself has serene depth, and the process is antique. Astronomer John Herschel invented cyanotypes in 1842 in order make copies of notes and tables; the first blueprints were cyanotypes. His family friend botanist Anna Atkins took the method a step further and used it to make photographs.

The technique is endlessly adaptable. “Out of the Blue,” curated by Michelle Law at the Provincetown Art Association and Museum, features three longtime Cape Cod artists who, hewing to the tradition of Atkins, push and prod at the pliable medium.

Cyanotypes are made by painting an iron-compound emulsion onto a substrate, usually paper. The emulsion dries, and then a negative or a positive (Atkins used plants) is placed on top and exposed to ultraviolet light — the sun or a sun lamp. A water rinse fixes the image. The iron produces that sumptuous Prussian blue. The process is hands-on and potentially toxic, a far cry from the virtual manipulations of digital photography.

But this is the 21st century. In “Out of the Blue,” Rebecca Bruyn marries analog and digital methods, shooting images with her iPhone to create large, 16-by-16-inch negatives. She totes those outside to make cyanotypes. Her photographs of older houses in Provincetown reflect on the vernacular architecture of this small town.

Because these are cyanotypes, they already read like relics. The digital images are sharp, but their edges sometimes swim. In “160 Commercial St., c. 1820,” a cupola and two chimneys appear on the verge of dissolution, as if the blue is time’s mists settling onto and eroding away the house.

Bruyn has a sharp eye for the compositions found in the angles and planes of Provincetown’s clustered clapboard houses. She amplifies the effect in a group of three photographic collages: “Above the Rooftops,” “Looking Out, Looking In,” and “Front Porch.” The collages, mounted on boxes that jut from the wall, lead the eye through, inside, up, and over in a way that evokes the cheek-by-jowl, nooks-and-crannies structures and spaces of this town.

Amy Heller’s earlier pieces, dating back as far as 2006, are spooky and typological. “Doll Triplets” portrays three limbless, numb-faced antique dolls floating out of the blue as if they’ve been entombed in a shipwreck. Heller’s cyan backdrop appears almost generative — the stuff of mystery, a depth from which images arise.

Her more recent, increasingly nuanced works veer from traditional cyanotype printmaking in fresh ways and shine a light into that mystery. In a series of terrific prints on silk mounted on light boxes, she layers negatives, positives (such as a trailing sprig of seaweed, a nod to Atkins), and more to create lusciously aqueous fields.

“Liminal Jellyfish” is as vividly vertical as a classical Chinese landscape painting — a force in Chinese art through several dynasties. It’s easy to see a craggy mountain and a storm-tossed sky here, but Heller’s rippling, sun-bleached emulsion and the moiré effect of layered silk make that association deliquesce into an intimate undersea experience, complete with passing jellyfish disquietingly close to the surface.

A photographer’s emulsion is like a potter’s glaze; mix up the chemistry and it alters the effect. Midge Battelle experiments, tossing spices, salts, vinegar, and soap suds into what she paints on the page. For “Pilgrim,” she exposed such a brew to UV light in a form shaped like the Provincetown Pilgrim Monument landmark, turning that tower from granite into luminous sea green spangled with blue — or from a phallic declaration commemorating the Pilgrims’ arrival and subsequent takeover of Native lands into a slyly mystical inquiry.

Batelle’s “Saint Joan” recalls the coat of arms granted to Joan of Arc’s family by King Charles VII around 1429. The heraldry features a sword down the center of an azure shield with gold fleurs-de-lis on either side. Battelle’s dazzling version peers directly down into the center of a deep blue blossom, petals languorously splayed, and bisected down the middle by a slash of pale blue light. The fleurs-de-lis are echoed in several delicate sprays like baby’s breath that whirl over the central flower and its surroundings.

As in “Pilgrim,” in “Saint Joan” Battelle collapses a hard-wrought symbol into something more elusive — a passion, the flowering of an inner truth. Blue is an apt color for such things: easy to lose yourself in. Add to that the touch of hand-painted emulsion, the kiss of the sun, and the patience and uncertainty of the process, and you can see why cyanotypes have never lost their magic.

OUT OF THE BLUE: Cyanotypes by Midge Battelle, Rebecca Bruyn, and Amy Heller

At Provincetown Art Association and Museum, 460 Commercial St., Provincetown, through Nov. 13. 508-487-1750, www.paam.org

Cate McQuaid can be reached at catemcquaid@gmail.com. Follow her on Twitter @cmcq.

Work at Boston Globe Media