It's usually a very long process. Something will interest me, and I'll read about it. But it usually doesn't become an idea for a novel until I find something else about it. This is often by chance and often can take years. For my new novel, Sweet Bitter Cane, I read the first idea about it in 1989, or so. But without really trying, I kept hearing small bits of information until someone gave me a folder with documents relating to the topic. The thing is that whilst this folder formed the backbone of the novel, without the prior knowledge from the last 30 years, I probably wouldn't have read it with such interest or understanding.