When a publisher proclaims a book a classic, as Penguin has done for the last 75 years with its Classics series and since 1961 with its Modern Classics spinoff, it raises a slew of potentially thorny considerations. What distinguishes a book as a classic? Who gets to make the decision? Will today’s classic, let alone 50 or 100 years from now, still be a classic?

“It’s a really slippery term,” concedes Henry Eliot, who has published a book on the former and is preparing to publish The Penguin Modern Classics Book on the latter. “People have made sense of it in a variety of ways,” he adds.

“Ezra Pound’s term is the one I use the most. He said that a classic is timeless not because of any structural laws or standards that it satisfies, but because of an inexhaustible inherent freshness. And it resonates with me.”

When it comes to who makes the decisions, Eliot argues that rather than boxing off the literary landscape by publishing a stock of classics, Penguin editors are really opening it out and encouraging readers to extend their views. Both series have significant inequalities – four-fifths of the Modern Classics stable are male, and nine out of ten are white – but Eliot argues that things are improving. “A classics publisher’s job is to identify and correct these imbalances,” he adds.

Another, less vexing point, but one that has certainly kept many Penguin designers up at night over the years, concerns exterior rather than internal freshness: How can you make a classic-worthy cover?

According to Eliot, the answer is “not easily.” “This idea that the books need to be beautifully designed has been built into the DNA of Penguin from the beginning,” he explains. “If there’s one thing that has defined the Penguin design ethos, it’s a kind of elegant simplicity – a Penguin cover is deceptively simple.” Putting things together takes a lot of time and effort.”

Eliot’s new book begins with a section on how cover design has changed over time, and you can see the subtle but noticeable modifications made by successive art directors throughout the decades (the Modern Classics series turned 60 this year). Dominant colors (orange, dove grey, eau-de-nil) fade away, just to reap reappearance in subsequent rounds.

After great deliberation, typefaces are phased out and replaced with more modern-looking alternatives. Grid layouts are enforced – many 1960s covers were produced using the so-called Marber grid, which divided the publisher’s logo, title, author’s name, and picture – only to drift or be entirely redone within a few years.

Some of Eliot’s favorite covers came from the 1960s, when the Modern Classics series was just being started. Penguin had relied mostly on typographic designs from the start, but by the late 1950s, images were becoming increasingly prominent. Penguin covers got more flamboyant and bizarre as younger designers and artists were recruited in and allowed much more artistic license to match the content they sold.

Eliot says, “but within that quite muted, subtle framework, the art directors were commissioning these sometimes really shocking and startling original images from the illustrators of the day.” David Gentleman, Michael Ayrton, and a teenage Quentin Blake were among those charged with illustrating Evelyn Waugh’s books.

Waugh’s mordant humor and strong awareness of life’s absurdities are captured by Blake, whose irreverent, scratchy style was well established. The work of André Francois, a Hungarian-born French cartoonist, is much more disturbing. “Where each eye of the face is made up of a mouth with another set of eyes,” Eliot says of his cover of William Faulkner’s The Sound and the Fury. It’s simply such a terrifying, eye-catching sight.

There’s something nauseating and vertiginous about it that reminds me of Escher or one of Borges’ short novels.”

The artists experimented with the shape in a variety of ways. The masculine figure in the front of Carson McCullers’ The Heart Is a Lonely Hunter – one of the series’ early novels – looks to be resting against the side of the book, as though held up by the designer’s carefully constructed borders, according to Eliot.

This promotion of original artwork lasted just a few years, yet it resulted in over 100 covers. The designers “began to increasingly use existing artworks” after 1963, according to Eliot, “the idea being that the cover artwork was roughly contemporaneous with the text, so you get an instant visual link to what you’re reading.” As a result, a cover of Virginia Woolf’s To The Lighthouse displays a piece by Duncan Grant, a Bloomsbury Group member.

The covers have remained eye-catching and brilliantly crafted to this day, but for a short time in the early 1960s, Penguin let its hair down and exhibited its wilder, stranger side. “The best covers find a way to make new titles intriguing while also making well-known authors appear new and irresistible,” adds Eliot. By that standard, these early Modern Classic covers were a wild success.

Thanks to at The Guardian whose reporting provided the original basis for this story.