Art restorers have uncovered a self-portrait of Rembrandt which had been retouched hundreds of years ago to feature a Russian nobleman, a museum says.

Layers and layers of paint were painstakingly scraped away to reveal the original picture of the Dutch master, complete with the round chin and gentle eyes common to other self-studies.

[Unsold portraits] were eventually recycled... by Rembrandt himself or by one of his pupils Rembrandt House museum

The painting was first done in 1634 when Rembrandt was 28-years-old, according to the Rembrandt House museum in Amsterdam where the work is now on show temporarily.

It was probably painted over by a student of Rembrandt who recycled works that had not been sold to save money.

Museum spokeswoman Anna Brolsma said Rembrandt's pupil added earrings, a goatee beard, shoulder-length hair and a velvet cap to make it appear to be a Russian aristocrat.

Signature clue

Various cleanings of the portrait since 1935 had begun to reveal what lay underneath but the final work was carried out by the Rembrandt Research Project, a group of scholars whose task is to authenticate the hundreds of paintings done by Rembrandt van Rijn.

Ms Brolsma said the group were asked to investigate the piece by an unnamed French private collector in 1995.

Although the portrait clearly resembled Rembrandt and bore his signature, the researchers at first ruled out that it could be genuine because it lacked the master's finesse.

It took them six years to remove the layers of added paint with a scalpel.

The museum said: "Rembrandt must always have had one or more self-portraits in stock. Some of them remained unsold. These 'wallflowers' were eventually recycled... by Rembrandt himself or by one of his pupils."

It was unclear how much the wood-panel painting, 70.8 by 55.2 centimetres (44.3 by 34.5 inches), was worth, but recent Rembrandts on the market had price tags of more than $30m.