LONDON, March 2 (Xinhua) -- A rare painting used more than two centuries ago in the campaign against the African slave trade is to go on public display for the first time since the early 1800s.

Britain's International Slavery Museum in Liverpool has acquired the painting by an unknown artist which shows a shackled and kneeling slave on a sugar plantation in the Caribbean.

The painting carries the legend "Am Not I a Man and a Brother" and has been privately owned for many years.

It is based on a design commissioned by the Committee for the Abolition of the Slave Trade on July 5, 1787, and is considered to be one of the first instances of a logo designed for a political cause, and used by the famous English potter Josiah Wedgwood.

National Museums Liverpool (NML) say there is no evidence of the painting ever being on public display.

"We imagine it may have been used to campaign for abolition in the 1800s. It is a significant acquisition for the UK, and only the second known painting to exist featuring this motif, the only other being 'The Kneeling Slave' at the Wilberforce House Museum in Hull," said an NML spokeswoman.

The artist of "Am Not I a Man and a Brother", although unknown, has revealed aspects of his or her profile in tell-tale traces across the canvas.

The style points towards a skilled British amateur, while the application of paint hints at a familiarity with the medium of watercolour.

The artist may have been a travelling, itinerant artist, or alternately someone established in the picture's town of origin, which is as yet unknown.

NML pointed out that interestingly the painter makes a number of fascinating departures from the commonly known famous version of the motif propagated by Wedgwood, "Am I not a man and a brother". In a curious rhetorical twist, the artist has inverted the second and third words of the established accompanying phrase. The foot of the canvas reads "Am Not I a Man and a Brother" spelled out in emphatic capital letters

Stephen Carl-Lokko, curator at the International Slavery Museum said: "This acquisition represents the first painting ever to be acquired by National Museums Liverpool to depict the powerful and resonant iconography of abolition."

"The painting is a remarkable surviving product of the early phase of the British movement to abolish the Transatlantic Slave Trade during the 18th and 19th century," said the curator.

Following restoration and cleaning work by experts, the painting will go on display towards the end of 2018.