Underneath the traditionally low-key librarian garb hides a living gallery of tattoos, with everything from treble clefs to tribal designs inked into the skin of staff members.

Cataloguers, contractors and other employees stripped down yesterday as part of the library's latest project on body art, but participant Marion Kruger said they were showing more than just skin.

"For me, this tattoo is about telling the world what I am and putting myself out there," she said.

"I think a lot of people use tattoos to express their personality and things about them that are kind of subversive or might otherwise be difficult to express."

As a cataloguer, Ms Kruger said her role of invoicing and itemising was stereotypically librarian and a huge contrast to the pin-up style ink on her arm.

"I got it done as a representation of my lesbian identity as a femme," she said. "Most femmes are invisible in society. They look just like an average straight woman."

The design was three years in the making and took three hours to complete, but it's not the physical pain or the hundreds of dollars making Ms Kruger hesitant about returning to the tattoo parlour.

"I'm very conscious of the permanence of them," she said.

"I'm thinking about my next one but I haven't even booked an appointment yet, because I want to make sure it's just right before I get it done. I really love having them but I can't just get them if they don't mean anything."

The National Library's image content coordinator Kate Ross said the idea of documenting these expressions of "secret self" was borne out of a brainstorming session several years ago.

"We started by wanting to look at not just tattoos but scarification, piercings, body painting," she said.

"We've dug out some culturally significant images from the past and we've got some great contemporary photography. I think something like body art and tattoos are a really big part of Australian life these days."

The National Library's head of publishing, Susan Hall, said the book, to be published next year, would also feature some of the stories behind individual tattoos.

She said the project was a little unusual for the library, but showed the variety of what could be found within its walls.

"There are so many interesting things in the collection," she said.

"There's a lot here for people to discover."