Authenticity is the Grail most production designers seek, though they’re not above a little trickery to achieve it.

Outlander” designer Jon Gary Steele reports producers “didn’t want anyone watching to say, ‘Oh that’s not right,’” so the team sought to present Starz with “an 18th-century slice of life in Scotland. Architectural detail, drapery, props, all of it authentic.”

Still, incessant Scottish rain forced them “to build more than we might normally — tons of big sets, furniture. We took places and turned them into villages and taverns. But all designers love to build. That’s the fun part!”

Bruce Robert Hill’s marching orders on Fox’s “The Last Man on Earth” (pictured above) were to create a believable post-apocalyptic Arizona, but with a wry twist. “They didn’t want cars parked askew or debris all over the place. … They wanted it to look a little more vacant, as if everyone had left for the weekend and just never came back. We had to dress all the locations with truckloads of brown vegetation, as if it had been neglected for years.”

Whenever AMC’s “Mad Men” called for Gotham haunt Pen & Pencil, Dan Bishop’s team swooped down on Cole’s, a longtime downtown L.A. eatery. “We’d have to pull out all the glass of the facade that had Cole’s lettering on it,” he recalls, “then switch out most of the bottles, the glassware, the barware….We’d make fake thermostats out of cardboard, spray them with hammer-finish paint and slip one over an existing alarm box.” Outside, “you’d stick in some trash cans, or park a period truck to catch the eye.”

Such trompe l’oeil, Bishop believes, is “a studied craft, to a certain extent. We develop artifice going along to make things a little quicker, a little easier.” Or, he adds, “a little cheaper.”