One of a set designer's mandates is to understand the time period and milieu of a play's setting. Even when you have a dramaturge (a production's Official Research Guru), it's usually still the set designer who is the authority on the visuals. Dramaturges concentrate on aspects that affect actors and director more than set, while set designers have professional interest in architecture. And interior design. And furniture. And...
So it's your job to know what the time period looked like. Plus, as much as possible, to understand the logic - economic, construction, social, artistic - behind why it looked as it did.
Recently I've been researching the countryside and villages of Connemara, Ireland, Victorian-Gothik mansions, ancient Egyptian monuments, and office spaces in 1919 New York. A nice varied menu!
The law office of R. Y. Williams in 1919, part of the Santa Ana Public Library's History Room Photograph Collection
Here's the most inspiring photo I found for Ghost Writer. Though this law office pictured was on the west coast, not in New York, other photos showed it was characteristic of the time.
What I found fascinating as a scenic designer was the spartan quality of the room: the severe wooden furniture; the contrast between dark woodwork versus plain paint; the rectilinear geometries, with only curved chair arms for relief; the details of picture rail and paneled door with textured glass; and the bare, bare walls - that ad-calendar the only decoration.
In my interpretation for the set of Ghost Writer, I added an opened transom above the door for a little 3D-ness and more verticallity for Circle Theatre's short space. (More on my version of that calendar HERE.) But though our writer's office remains bare looking, we did add books (from the script), soften the color contrast into sepia tones, and add a wainscot of bead-board - because spartan was a bit too spartan onstage for a romance!
A theater set needs to be true physically - to its time or location - but it must also be true emotionally.
Many thanks to libraries and collections like the Santa Ana Public Library, that generously make their collections accessible to the public online. It's impossible for a designer to own every book on every topic or even to find all information needed locally, so I'm very grateful.
(BTW, I believe copying this photo here is Fair Use, as I'm teaching theater set design, but please let me know if I'm mistaken and I'll remove it instantly. Please don't copy it elsewhere, Dear Reader, without researching restrictions HERE.)