'Die Waage der Hinternmondgerechtigkeit' by Friedrich Schroder Sonnenstein (1892-1982) is valued by Anderson & Garland at £15,000-20,000.

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The Heppe collection of close to 400 canvases was assembled from the 1970s onwards by Christian Heppe, a pioneer of the bottled water industry as founder of Hildon Mineral Water and one-time commercial gallery owner.

Heppe’s passion was for Art Brut, the label created by French artist Jean Dubuffet to describe art created outside the established art scene. Many of the works are associated with the Haus der Kunstler (House of the Artists) at the Gugging psychiatric hospital, near Vienna where patients showing significant artistic talent live independently and focus on their creative work.

Famously, David Bowie’s visit to the Gugging clinic with Brian Eno in 1994 inspired his Outside album.

The Heppe collection has made its way to Newcastle-on-Tyne from a warehouse in Southampton where Heppe’s sometimes huge canvases were covered under drapes.

Specialist John Anderson describes the sale as a career highlight and a consignment that reflected “a bit of good luck and a lot of hard work”.

“Nearly every artist from within the Outsider movement is represented in the collection. We’ve had interest from collectors from every corner of the globe. It’s one of the most important single groups from the Gugging school to come on to the market since 2010.”