The easy answer is, there is no easy answer, because for one thing, who is to say definitively what is the feel of an era? My editor flagged words as sounding too modern that came straight out of period literature, but I changed them because I decided actual accuracy wasn't as important as not jarring the reader's perception of accuracy. There is also the concern of not confusing a reader. In the 19th century, and into the 20th, oftentimes "dinner" was the midday meal and "supper" the evening meal. My grandparents still say supper. Lunch was not in such common use. But nowadays supper has fallen out of favor and many readers would be confused by the mid-day dinner/evening supper situation, so I stick with lunch and dinner.
Period voice is, for me, intuition as much as anything. But where does the intuition come from? Books!
Tip #1: Read a lot.
I am a non-fiction ADDICT. I buy some novels, sure, but what really opens my pocketbook is a good non-fiction book. My reference library is just to the right of my desk. Lots of books aren't even in there because they are scattered everywhere. (And of course, I'm also a heavy library user!)
If you're trying to capture a period voice, you have some options:
--Reading novels or memoirs/travelogues/whatever written in the time and place you are trying to capture
--Reading non-fiction about the era or collections of diaries and letters
--Reading novels/memoirs set in the era by someone who lived in the era, but written afterward...it might change their voice, but it might also be a bit easier to read
I recommend some of all of the above to get the most rounded picture. And what are you trying to pick up while reading?
#2: Pay attention to small details.
For instance, Magic Under Glass, pg. 28: "The servants filled a tub with hot water from brass canisters." I could have left off the brass canisters, certainly, and just say they filled the tub. And one mention of brass canisters or the silk lining of a carriage won't fill out the book. But when you slip them in here and there, it helps set a mood and paint a picture. These are the sorts of things I take note of when I read, to stick in later.
You can also take note of the words people use. The Betsy-Tacy books, for example, are full of natural teenage dialogue that doesn't sound like nowadays, the kind of thing you could jot down or the rhythms of which you can absorb if writing an early 20th century American novel:
"I don't see anything so special," Tib remarked.
"Why, we're sitting here drinking coffee," Betsy repeated somewhat lamely. "And not just for a lark."
Tacy's thoughts followed hers.
"We're actually juniors," she said, "stopping in for coffee after shopping, not freshmen or sophomores pretending to be juniors stopping in for coffee after shopping."
Tib looked confused. "You usually take chocolate. I've just got you in the habit of coffee because I come from Milwaukee."
"But Tib!" Betsy cried. "That isn't the point. The point is that we're so frightfully old."
#3: Which brings me to the mood and rhythm...
Even though so far I write fantasies inspired by historical periods rather than actually history, the mood and rhythm of the language is a huge part of creating the world. Between the Sea and Sky was intended to take place around 1800. I feel that writing around 1800 was often actually simpler-sounding than the Victorian period. Marie Antoinette's letters, for instance, often sound very modern to me. Of course they're translated, but still. Jane Austen is wordy but not as wordy as Dickens! So the language in the book I tried to keep straightforward, a little bit "classic" perhaps:
Ginnia led Esmerine from the dim bedroom. Dusk had crept up almost unnoticed until Esmerine came into a dining room lit by a candle and glowing hearth-fire. Sometimes the mermen started a fire on the islands for some purpose or another, but only certain men knew how, and children couldn’t come near, so Esmerine had never been close enough to fire to feel the heat. An older woman with gray curls falling across her cheeks beneath a squarish black cap was sitting quite near it, smoking a pipe. Could this be Belawyn? Esmerine couldn’t believe a mermaid would smoke.
Ginnia went to stir the pot while Swift waved her to an empty seat. Alan was pouring red wine. “Esmerine, do you want wine or water?” he asked.
“I’ve never tasted wine.”
He poured a little in a cup and handed it to her. She took a sip and was surprised it was not at all sweet or salty, just nasty and like nothing else she had ever tasted.
Swift laughed. “She doesn’t like it.”
Magic Under Glass is inspired by the Victorian era, and the voice was more "affected":
I joined Mr. Parry in the tower—not the top of the tower, which must have been shut off like the rest of the upper stories, but the second floor, a small circular room with three huge windows overlooking the woods. A table already bore a spread of food: thin soup, more crusty bread, and some kind of drink in a silver pitcher. A footman waited in the shadows, in the invisible way of servants. Mr. Parry was standing, waiting for me to arrive before he took his seat. The footman pulled out a chair for me.
I smoothed my skirts underneath me and took the heavy, carved chair.
“A pity it rains,” Mr. Parry said, pouring himself the drink: something red and bubbly. “I suppose the gardens had to wait.”
He held the pitcher over my glass and I nodded. “Yes, sir. I don’t mind. I explored the house, the library—I spent ages reading. The sun might have set without my notice.” I chose my words carefully, feeling the need to make proper conversation, whatever that meant. I’d read it in stories, but I’d never shared a table with a gentleman before.
I'm working on a Weimar Berlin inspired setting now, and the voice in this one becomes more modern, a tad choppier and more cynical:
Thea hoped for a moment that it would be one of the old cakes, but of course it wasn’t. Mother didn’t even know how to make a cake right anymore. She used to make buttery pound cakes, and moist apple cakes, and gingerbread… When Thea opened the pantry, she saw the same old chocolate cake sitting there. It wasn’t even a good chocolate cake. Too dense, with a strange sour taste.
Still, she sliced it and got the coffee going. She set the table with plates and cups, all chipped by now from something or another, and when all was ready, she pulled Mother away from the window and into a chair.
Mother picked at her cake. “I do like this cake.”
“I’m glad you do, because you made it.” Thea chewed on hers, sorry that good flour and sugar had gone to waste.
(I used three eating scenes, to try to offer the best comparison...
And one more note, because good HEAVENS this is going on forever:
#4: Don't forget to consider the age, sex, class and location of your character(s) when shaping the voice. My great-grandmother was born in the teens and grew up in Ohio, and the letters she sent to me as a kid and the way she talked always carried the flavor of an older era. Consider the past of your world too! And of course, a character's class can have a huge effect on their speech.
Of course whatever voice you use, it won't work for someone. For every two people who praise Magic Under Glass's voice, I see a review that said it was too "precious" or something. But at least I know it's as accurate as I can make it, being a modern girl, and that's the best you can do!