(Edinburgh) -- A previously hidden self-portrait of Vincent Van Gogh is being revealed. The National Galleries of Scotland discovered the artwork on the back of the canvas of one of the artist's paintings. It was found under layers of cardboard and glue behind his 1885 painting "Head of a Peasant Woman" while performing a routine conservation X-ray. It's believed the self-portrait is part of an experimental series. Five similar works are on display at the Van Gogh Museum in the Netherlands.