Going Back in Time
Historical pictures must give us two things: context and narrative.
For context, the drawing or painting must pull us in, placing us inside the setting ("Ah, that’s a gas-lit street scene!"). For narrative, the artist places the characters and elements within the setting.
The watchword with historical paintings is "accuracy." (No, they didn’t have rifles in the American Revolution!) Woe betide the artist who paints it wrong! So historical paintings always require a fair bit of research.
Even though the client might give the illustrator some direction as to what should be in the final painting, one shouldn't venture back in time lightly. Luckily, I enjoy the research almost as much as creating the illustration, and I strive to create paintings that are as historically accurate as my research material allows.