If you’ve ever made a scrapbook or created a video mash-up, you probably didn’t realize you were practicing a 19th-century illustrative technique.

Grangerizing, which became popular in the late 1700s, is the process of extra-illustrating, or enhancing books with supplemental materials such as photographs and maps.

The Folger Shakespeare Library’s new exhibit, “Extending the Book: The Art of Extra-Illustration,” details the process from its early days as a way for people to color the books they read to the elaborate paintings that grew out of that.

Amy Arden, a communications associate for the library, likened the process to modern-day information and artistic mash-ups.

“You’re taking material and adding to it in a very unique kind of way,” she said.

The term grangerizing stems from 18th-century author James Granger, who inspired a long-lasting trend. Granger published his “Biographical History of England” in 1769, accompanied by a list of photographs of the people mentioned and where a reader might find the images. According to Arden, people used the resource to track down photos and removed them from other books in order to include them in their copies of Granger’s work.

The practice became quite popular, and people started to grangerize their other books as well.

Arden said that illustration had a much broader meaning during the 19th century than it has today. Extra-illustration included any kind of supplementary material that people believed would add to the experience of reading the book. Once the additions had been made, many would have them professionally bound, and the updated version was often much larger than the original.

In addition to enhancing books with photographs of historical figures and characters, many people added playbills and letters to copies of Shakespeare’s plays as keepsakes and to personalize the work.

Augustin Daly, a 19th-century theater producer in New York City, filled copies of his plays with sketches of costumes and even letters from certain notorious literary figures of the day.

In one book, Daly kept a letter from Samuel Clemens, better known as Mark Twain. The writer had attended a party Daly threw and asked the host to give his regards to the actress Virginia Dreher, with whom he had been chatting throughout the night.

Sometimes, amateur artists would replicate great paintings in order to illustrate particular works. H. Jeayes, who did several paintings for extra-illustrator George C. George, created a watercolor that was very similar to Francesco Zuccarelli’s oil painting “Macbeth Meeting the Witches.” Although not an exact copy, the influence is evident in the choice of colors and the positioning of the figures.

Alexander Meyrick Broadley, a fan of the actor David Garrick, turned Percy Fitzgerald’s two-volume “Life of David Garrick” into a 17-volume work by adding photographs and even entire additional texts to what Fitzgerald had written.

Although grangerizing became quite popular across different social classes, there were some outspoken critics. Some declared it a “pernicious” practice and decried the destruction of perfectly good books for the sake of adding to another.

In some instances, the art lost its impact when moved to a new volume. One extra-illustrator from Kansas removed a picture of Cicero from a book about the lives of emperors and moved it to another that had only a passing reference to the Roman leader.

When J. Moyr Smith’s “The Discovery of the Murder,” depicting Lady Macbeth, is moved from an elegant copy of “Macbeth” to “The Pictorial Edition of the Works of Shakespere,” it loses some of its original character because of the new setting.

On the other hand, extra-illustration was also used to create truly beautiful manuscripts. W.H. Drake painted thousands of watercolors around the text of a 20-volume set of Shakespeare’s works. His paintings of Hamlet and the ghost, which are part of “Extending the Book,” show how significantly thoughtful illustration can add to the experience of reading the play.

Pinckney Marcius-Simons took that a step further, painting a gorgeous, vivid watercolor scene from “A Midsummer Night’s Dream” over the text of that play. It is a French translation, and although the painting corresponds to a scene on the page, it is no longer possible to read the text.

“Extending the Book” is a somewhat quirky and fascinating exhibit that follows the organic creative process at a very common level through the past three centuries.

The exhibit will be on display through May 25.