Deborah Heiligman is the author of around 30 books for young readers, including the 2009 biography of Charles Darwin, Charles and Emma: The Darwins’ Leap of Faith, a National Book Award finalist, which focuses on the importance of the seminal scientist’s marriage. In her newest book, Vincent and Theo: The Van Gogh Brothers, she explores the painter’s deep relationship with his brother. Heiligman spoke with PW about the difference between writing fiction and nonfiction, how a book idea grabs her, and trying her hand at watercolor painting while working on Vincent and Theo.

How did you come to writing for children?

It’s a story that combines romance and work. My first job after college was working for a magazine called Moment, in Boston. It was a liberal Jewish monthly and I was an assistant editor. Soon after I started, a man who had had my job before me came back to visit. He had moved to New York City and now worked at a science magazine. So we met and within a few months we started dating. After about a year and half at Moment—where I learned a lot—I realized I wasn’t getting enough writing experience. Plus I wanted to move to New York to be with Jonathan. I interviewed at Scholastic for an opening on a magazine for fourth graders. When they gave me the trial assignment, I found I loved it! Maybe because I was still a fourth-grader inside. Anyway, I got a job offer and a marriage proposal on the same day. Jonathan and I are about to celebrate our 35th anniversary.

I worked at Scholastic for four years. Then I had a child and decided not to go back to work, but started freelancing instead. I wasn’t writing only for children then, but for other publications, too, like Ladies Home Journal. But after I sold my first book, I moved to writing only for children.

What was that first book?

It was a rhyming picture book called Into the Night (1990), illustrated by Melissa Sweet—it was her first book, too. It was published by what was then Harper & Row and went out of print quickly because our editor left. And then very soon after that, Harper and Row became HarperCollins and our book just got lost in the shuffle. That was very sad for us.

You write across all genres—nonfiction, fiction, picture books—and for all age groups. How do you decide what age a book will be written for?

It’s kind of a mystery to me! I think an idea just comes to me for an age. For example, with The Boy Who Loved Math (Roaring Brook, 2013)—probably nobody in her right mind would write a picture book about an obsessed mathematician, but when I heard Paul Erdos’s story, I knew I wanted to write a picture book about him. And then with Charles and Emma and Vincent and Theo—well, their stories clearly seemed like a good fit for YA.

Do you have a favorite audience to write for?

I love them all, honestly! I love writing for little kids and I love writing for teenagers, and I hadn’t written true middle grade for a while, so I’m loving being in that mindset now. I’m working on a middle-grade nonfiction book about a World War II disaster and I keep a note on my desk that says, “Think Younger.”

Do you prefer one genre over another?

When I’m writing fiction, I wish I were writing nonfiction, and when I’m writing nonfiction I wish I were writing fiction! But seriously, I feel so fortunate to write in many genres. I like to say that the best part of my job is that I am never bored. I once wrote an entire fictional picture book—Cool Dog, School Dog (Marshall Cavendish, 2010)—in the shower, in a waterproof notebook.

Is your writing process different depending on the genre you’re working in, or which audience you’re writing for?

I think that whether I’m writing fiction or nonfiction, I am a storyteller. I like to use a clay and marble analogy when I talk about the difference between writing fiction and nonfiction. When I write fiction it’s like making a sculpture out of clay. I have to create something from a lump of clay, building it, forming shapes, making pieces that go together. But with nonfiction, it’s like making a sculpture out of marble. The story is there; I have to find it by chipping away at what doesn’t belong. Slowly you begin to see the shape of the piece. In both cases it’s about getting to the heart of the matter by asking yourself over and over again, “What is this book about?”

I’ve done much more nonfiction than fiction, and the process is always the same, no matter what age group I’m writing for. I always do a tremendous amount of research and the further along I am in my career, the wider and deeper my research is. When I’m researching I focus almost exclusively on primary sources. I only go to secondary sources if I want to check something. I want the book to be mine.

Your books encompass a tremendous range of subjects. How do you choose your subjects?

Since moving out of the phase where I said “yes” to anything an editor asked me to write, I’ve been writing about things I want to learn about—things that grab me by the heart, or by the soul. For example, my current book on a World War II disaster began when my editor, Laura Godwin, showed me a photo she had taken a few years earlier in the Imperial Museum in London. It was of a child’s life jacket. She said, “See if this grabs you.” She was my editor for Charles and Emma and for Vincent and Theo and she really understands me. She knows what grabs my heart.

How about Vincent and Theo, then? How did this book grab you?

Actually, I had a contract with Laura for a different nonfiction book, but it wasn’t working. I just didn’t have enough information to write it as nonfiction, but it took me a long time to figure that out. While I was worrying about that book, my husband and I went to Amsterdam and we visited the Van Gogh Museum. Next to one of the paintings I saw a note about Theo and how he supported Vincent. I had forgotten Van Gogh even had a brother. I said, “When I finish my other book, I have to write this book.”

When I finally realized I couldn’t write that original book, I said to my agent—who was then Ken Wright—“I only have one other idea. How can I go to Laura with only one idea?” He encouraged me to talk to her, and I did. I started telling her about Vincent and Theo and Laura said, “Hold on.” She pulled out a graphic novel—which she had gotten at the same museum in Amsterdam some time earlier. It was a partly fictionalized story about Vincent and Theo. She said she had been thinking that somebody needed to write the longer, true version of their relationship.

What was it about Van Gogh that grabbed you? Have you always loved his art?

I have always loved his art. I was 13 when Don McLean’s song “Starry Starry Night” was released, and I had read Irving Stone’s Lust for Life about him as a kid, too. But Van Gogh was so famous that I had never thought about writing about him. It’s really hard to write about famous people. I have to ask myself, “What can I bring to this?”

It’s a very long book, but obviously you didn’t put in every single thing that happened in Vincent’s life. How did you choose what to put in and what to leave out?

With Charles and Emma I had a mantra: it’s a love story. Everything that I put in had to be in service to that love story. Vincent and Theo is also a love story, but it’s the story of the coming of age of an artist, too. So I put everything in the frame of that relationship—for example, Theo was telling Vincent to lighten up on his paintings and to use more colors, because Theo, being an art dealer, was seeing the new work of the Impressionists. Those are the kinds of things somebody else would not have written about Van Gogh.

What kind of input did Laura have on this book?

I was having some trouble early on with the book; it was the famous-person thing kicking me in the butt. So I showed Laura a first draft of about 90 pages of mess. I knew I didn’t have “it” yet, so we had a conversation. It was kind of like a therapy session. She was brilliant. She gave me permission to tell the story I wanted to tell. One year later I handed in a complete first draft. While she had the manuscript, I had time away from it, which really helped. When I got it back, I was able to see it with a fresh eye.

How long did it take to write?

I started in 2011 and finished in 2016, so five years. Now, I did other things in between, but it really did take a lot of time for me to make it my own. It took a very long time for me to feel about Vincent and Theo that “they’re mine.” The day I felt that, I actually started to cry. It was an amazing feeling.

It was a hard book to write because it was so sad—I did a lot of crying while I was writing it. Their sadness, their loneliness—all that took a toll on me. I became so attached to them. I think the story of their relationship speaks to how much we need people in our own lives to support us; we need connection and support. That’s part of my vision of the book.

The book makes heavy use of their correspondence. Where are the Van Gogh letters kept?

Fortunately, all the letters—that we know of—are available online. Many people have published editions of selected letters over the years. The first one I read was the poet W.H. Auden’s edition. I took notes from those letters and asked myself, “Why did Theo stand by Vincent for all his life?”

In 2009 the British publisher Thames & Hudson published a six-volume set of all the letters, together with lots of art. Any picture Vincent references in the letters is shown in the book. This book is also available online—and constantly being updated—so I started by using that resource. Then my husband gave me a gift of the actual six volumes. That was my main source; it was published in conjunction with the Van Gogh Museum in Amsterdam, and whenever there was any question about anything, that was the source I trusted.

Are they in Dutch?

The early ones are in Dutch, then the later ones are in French. I read them in translation, but I also had some help from a Dutch friend who is a translator and even did some translations for me.

Did you go to the Netherlands or France while you were working on the book?

No. I thought long and hard about this. I had been to Amsterdam, Paris, and Arles in the past but I decided not to go back because I wanted the book to be about the emotional relationship. I didn’t want to be distracted by other things. I thought traveling to the places he lived might get in my way.

On the other hand, I really wanted to know what it felt like to be an artist. So while I was working on the book I painted a lot of watercolors. I was doing hands-on research. The first year I was working on the book I would read and paint. I just wanted to have some infinitesimal idea of what it was like to be an artist.

You’ve mentioned a couple of very different projects that you’re working on now.

Yes, the middle-grade book has the working title Torpedoed. It’s a great challenge for me to write it, but as much as one can love working on a book about a torpedo attack in which many children die, I am loving it. It’s fundamentally a story of survival and heroism. And of course an anti-war story. A lot to think about, research, and maneuver.

And then the picture book is about the geneticist Barbara McClintock and is tentatively titled The Girl Who Loved Science, as a follow up to The Boy Who Loved Math. It’s going to be illustrated by the great LeUyen Pham, who illustrated The Boy Who Loved Math, so I’m very excited to be working on it.

Vincent and Theo: The Van Gogh Brothers by Deborah Heiligman. Holt, $19.99 Apr. 18 ISBN 978-0-8050-9339-1