Years, not a season
A historical novel is a long tenancy. Research, draft, revision and the wait for a reader all happen inside the same century. Writers who choose a period because it is selling this spring often discover, in month fourteen, that they do not want to know what these people ate. The reader will notice the boredom before the writer will admit it.
Fascination is not a mood. It is the willingness to be interested on a dull Tuesday, when the scene is not a battle but a bill, a funeral, a quarrel about a dowry. If that Tuesday feels like homework, the century is wrong, however fashionable the jacket on the bookshop table.
A gap in the market is not a reason
Markets move. The Tudor court, the wartime wireless, the Regency ballroom — each has been declared full and then filled again by someone who could not stay away. A gap is useful later, when you are describing the book to an agent. It is a poor reason to begin. You cannot out-research indifference.
If two periods attract you, choose the one you already return to when nobody is asking. The shelf you browse without a project. The documentary you rewatch. The argument you have had more than once. That habit is the fuel. Taste can be educated; obsession is quicker.
The week in the library
Give the century a week before you give it a plot. Read one diary, one chapter of a social history, one newspaper or sermon, and write down only what surprised you. Surprise is a better compass than admiration. Admiration produces pastiche. Surprise produces questions a novel can use.
Then notice your boredom honestly. If the religion feels like an obstacle you hope to skip, you will write characters who also skip it, and the century will go thin. If the clothes, the law and the food start answering each other — what a fabric cost, who may wear it, what happens to a person who does not — you can live there.
Narrow until it is a life
“The Victorian era” is not a place. A decade, a city, a trade, a class of household is a place. The narrower the room, the more of it you can furnish. A novelist who knows one street in 1854 can imply a nation. A novelist who summarises a nation usually produces a textbook with names.
You are allowed to change your mind before a draft exists. You are not obliged to stay from loyalty to an idea you have not tested. Leave a century that bores you. The years you save will be the years the book needed.
Try this
Spend one sitting with a primary source from the period you think you want. List ten things that surprised you and three that bored you. If the boring list is longer, choose a different room in the same century — or a different century.