OXFORD, England — A series of boyhood doodles engraved on copper plates by English poet and painter William Blake around 250 years ago have been discovered by researchers using new technology capable of picking up the almost invisible etchings.

Blake, who became one of the greatest poets in the English language, had worked as an apprentice to engraver James Basire, who made pictorial prints, one of the main ways to print illustrated books at the time.

Blake's poem "And did those feet in ancient time", better known as "Jerusalem", is often considered England's unofficial national anthem, while "The Tyger" is a staple of English textbooks.

One of the previously unknown doodles depicts an arrow, a frequent motif across Blake's works, while another depicts a miniature face.

"When I first saw the face, it was a staggering moment. I almost fell off my chair," said Blake expert Mark Crosby who found the engravings. "I was looking back at something that had been made 250-odd years ago that hadn't been seen before."

Many of the engravings are invisible to the naked eye and were found using new, high-resolution scanning technology at the Bodleian Libraries at Oxford, to which the copper plates had been bequeathed in 1809.

The drawings appear on the reverse of Basire's copper plates, a space an apprentice might have used for practise.

That, along with the motifs represented in the drawings, points to Blake as their artist even though the plates do not carry his signature, Crosby, associate professor of literature at Kansas State University, said.

Crosby, whose research will appear in two peer-reviewed journals, said the discovery also provided other insights about Blake when he practised at Basire's studio.

"I think he's like any teenager, who possibly gets somewhat bored easily with doing this sort of very repetitious work, so he's doodling away."