Katherine Ashenburg has been writing nonfiction for decades, as an academic, a contributor to Toronto Life and the New York Times and author of four books. At 72, she is breaking into the fiction scene with her novel Sofie & Cecilia.

The book, inspired by two of Sweden's most celebrated painters, Carl Larsson and Anders Zorn, redirects the spotlight onto the lesser-known stories of their wives and the friendship between them that evolves over a lifetime. In the process, she paints a rich scene in early 20th century Scandinavia, in which history, art and sexual politics intersect.

Below, Ashenburg shares what inspired her foray into a new genre.

"One of the things I wanted to do in the book was write about imperfect relationships which still work on many levels. It's also about the very gradual growth of the friendship between Sofie and Cecilia. They were born in the 1860s, raised never to wash the dirty linen of the family in public. So it was very hard for women to have intimate friendships. As a matter of fact, I think my own mother didn't really have intimate friendships in the way that my generation and younger ones do."

"I had always loved the watercolours of Carl Larsson, but I'd never been to Sweden. The first time I went, my daughter who was working there, insisted that we find the village where he and his wife had painted and decorated their house. I realized that I knew nothing about their biography. I was just looking at these idyllic pictures of the rooms of his house, his wife and seven children. On that trip I learned that he and his wife, Karin Larsson [named Sofie in the book], had been educated at the Royal Academy of Painting and had the same training, but when they got engaged he said to her, 'Oh, did I mention that women can't paint? So you won't be painting after we get married.' So all of a sudden, I saw that underneath this beautiful surface of these watercolours was probably another story that was maybe less beautiful, but probably more interesting. I got interested in their marriage.

"During my three research trips to Sweden, I discovered the other most famous Swedish painter at the time, Anders Zorn. I learned that he was even more of a philanderer than was normal for most painters in those days and how his wife, of a very small Jewish community in Stockholm, became his dealer and curator. Although I don't know if the two women ever did become friends in real life, the story of their developing friendship became part of the book."

"I had been in this little informal fan club of Carl Larsson, with my friend the novelist Jane Urquhart and her husband Tony Urquhart, the artist, for a long time. When I got home from Sweden I called and told her that I found out something about the Larssons marriage on this trip and how Karin was forbidden to paint. I said, 'I'm telling you this as my present to you from Sweden because it might surface in one of your novels.' Jane writes a lot about visual artists and she said, 'No, I'm giving you your present back because this is your story.' I thought she meant that I had to learn Swedish and write a double biography of Karin and Carl Larsson and I said 'No, Jane. As crazy as I am, I'm not about to do that.'

"And she said, 'No, I don't mean that. This is your first fiction.' And she must have been either tremendously persuasive or it was the right time for me to start. So I would call her regularly during the 10 years it took me to write this book cursing her for setting me on this miserable path."

"I think nonfiction is like a continuation of school. You write paragraphs, then you learn how to write a book review and an essay, whereas writing a novel was so scary at the beginning that I had to pretend to myself that it was just like a non-fiction book. I needed to do my research, which I love to do. So I read everything that you can possibly read in English about Sweden at the time, Swedish art history, the Larssons, the Zorns and the milieu in which they lived.

"I've also done a lot of travel writing, so I knew how to get to places and figure out the spirit of the place. I went to their villages, houses, synagogues, art schools and things that they would have seen. So this was all very fun and very easy. The hard part was writing. I think I probably made every mistake in the How Not to Write a Novel book, which I never read. I wrote scenes out of order. I would write a scene just when I thought I could bear to write it and then I was faced with this puzzle at the end and had to put it all in order."

"One important moment for me was when another novelist friend read the draft and she said it was something between a biography and a novel. That was not what I wanted to hear, but it was so important to me because I realised that I had to throw out a lot of the facts and go for the truth because real life is messy and I had to make a novel that had some kind of shape. So that was a very big moment for me. As a fiction reader, it's just so thrilling to be able to make up your own stories."