As a former reference librarian, I love to do research. I confess to having spent half a day searching for the origins of the chocolate sprinkles to put on ice cream. I thought I'd failed, and got diverted into the history of the lollipop. Then, lo and behold! The same man invented the sprinkles. All this time spent so I could allow a character to ask for sprinkles on his ice cream in my 1920's novel, QUEEN OF THE MARDI GRAS BALL. This was an easy detail to work into the novel. Many other marvelous tidbits had to be set aside least the book start sounding like a non-fiction account of life in the Twenties.
How much historical detail to add? What to leave out? Usually, I try to work signs of the times into the conversation. People took picnic baskets and went out to watch the levee protecting St. Bernard Parish being blown up to save New Orleans. Surely, people would have talked or written letters about this event. On the other hand, it is not necessary to describe the making of bathtub gin, no matter how fascinating, to say someone is drinking it in a scene. I wish I had a formula to offer like fifty percent fact, fifty percent fiction, but I don't. I still haven't figured this out for myself. Just yesterday, I learned how a wigwam is built, step-by-step. Will I use this? Probably not. But it is just so tempting.