When you’re writing a novel set in a period that’s not your own, research is an inescapable part of the equation. Not that it bothers me—I love setting off on a journey of discovery into the ‘foreign’ yet teasingly familiar country that is the past, and on the way learn lots and lots of things, which will often set me off on new and intriguing paths. It is indeed often so much fun that it can be hard to tear yourself away from the research to begin the hard work of the book itself! And you also have to temper enthusiasm with temperance—to know the point at which enough research becomes too much. And not to paralyse your creativity with too much emphasis on logistics or facts—to remember you are not writing a historical textbook, but a historical novel. Over the years I’ve become familiar with those tipping points and now, by instinct, know when to stop—and not to become enslaved by historical fact. The trick is to learn enough facts and absorb enough cultural atmosphere to feel as though you are comfortable in that period; but not to think you need to know absolutely everything—after all, you don’t even know absolutely everything about your own times!
When I do research into a historical period, I look at a whole range of source materials. Though I do briefly look at secondary sources such as general histories of the period (and also books focusing on particular aspects of that period, say, clothes, transport, weapons, social or cultural developments, etc), the major part of my reading is done in primary sources: novels, plays, poetry, non-fiction of that period, letters if any have survived, and contemporary magazines. These give a much better and warmer feel for the actual atmosphere of the times than books written later, with the benefit of hindsight. You get a real sense of how people thought and spoke—and it can be really surprising.