Dee Ledger can remember exactly when she found solace, if not salvation, after the death of her 10-week-old son, Obed. It is where she found it, and how, that surprised her: in a colouring book.
Ledger, a former English teacher and hospice chaplain, had always been able to use words and prayer to find peace in difficult times and to help others do the same. But after her son died in April 2011, she needed something more, something different, to calm her nerves and help soothe her grief.
"I was looking for something quiet that could get rid of this restlessness," she says, to help quell the churning thoughts that made it hard for her to focus or sleep.
Back then, colouring books weren't the phenomenon they are today. Ledger found hers in a spiritual catalogue.
Now, of course, adult colouring books are ubiquitous, crowding bookstores and bestseller lists. Colouring-book groups have sprouted up everywhere - in cafes and libraries, on Facebook and Instagram.
Last year, an estimated 12 million adult colouring books were sold in the United States, according to Nielsen Bookscan. There are adult colouring books for hipsters, Dr Who fans, cat lovers, Taylor Swift devotees, and admirers of Supreme Court Justice Ruth Bader Ginsburg - pretty much anyone with a niche interest and a need to relax. In other words, everyone.
"It's easy to pooh-pooh colouring books as just another fad," Ledger says. But maybe, she says, we shouldn't be so dismissive: "Anything can be a fad, even prayer."
For Ledger and others, colouring books offer a real elixir, a way of getting past hurdles - mental, physical or both - that can't be replicated by more traditional approaches.
Joanne Schwandes, a 67-year-old Silver Spring, Maryland, resident, says that colouring books have boosted her confidence in fine motor skills weakened by a tremor in her arm. A Virginia mother says that colouring has helped her stay calm in the face of her son's violent behaviour. On one Facebook colouring group, members share their creations along with their stories of healing - using colouring as a tool against self-harming or as a way to manage the effects of physical illness or fend off depression and other difficulties.
Colouring books work like other mindfulness techniques such as yoga and meditation, says Craig Sawchuk, a clinical psychologist at the Mayo Clinic in Rochester, Minnesota. Such approaches work "almost like a volume knob to turn down the sympathetic nervous system, the stress response". Colouring can help slow down heart rate and respiration, loosen muscles and stimulate the brain, he says.
Colouring has a "grounding effect", he says, a benefit that can be amplified with deliberate focus on the process - "the gentle pressing of the crayon or pencil on the page, the texture of the paper across your hand, and the soft sounds of the colouring instrument moving back and forth in a rhythmic fashion," he says.
Although there have been no large clinical studies of using colouring books, the benefits of colouring are comparable to those of mindfulness practices, he says, which have been studied. And colouring can help with more severe problems beyond stress; Sawchuk spoke about one patient who used colouring books to stop an obsessive habit of picking at her skin.
Indeed, art therapists have been using colouring books for years. "There's a self-soothing meditative benefit because you are doing the same motion over and over, especially with symmetrical drawings," says Lina Assad Cates, a psychotherapist and board-certified art therapist in Washington who uses colouring books as part of her practice. "The books help create boundaries - the literal boundaries of the lines and the metaphorical boundaries for drawing healthy boundaries in relationships. There's also the potential benefit of just mastering something you've created."
This reflects Ledger's experience. "As a pastor, I am fascinated by how easily colouring becomes meditative," she says. "By selecting colours and working with the design, I find that I can lose myself in ways that are healing and creative." Ledger, who lost her husband to cancer in 2013, less than a year after giving birth to twins, spends about three hours a week colouring, mostly at night, when her children are asleep and she can sit quietly in the kitchen of her Rockville, Maryland, home and gather her thoughts.
"I'm not an artist," she says as she spreads out her works on her bed. And she understands that colouring is neither a panacea nor for everyone.
"If someone was grieving, I wouldn't just pay a visit on them and say, 'You should colour, and that would take your grief away'," she explains. "I don't believe that." But "being able to sit there and actually control that little world" inside a colouring book has been "really instrumental in my starting a new chapter of my life", she says.
"I don't know if you ever fully heal from loss and trauma. But colouring has definitely helped me start a new life again."