A print of a sea of umbrellas in the rain by a little-known Australian artist has fetched 10 times its top estimate .

Wet Afternoon by Ethel Spowers 

The growing demand for Picasso ceramics was in evidence at Christie’s in New York last week, where a collection of more than 150 earthenware plates, pitchers, plaques and vases sold out. Many pieces doubled and trebled their estimates.

The top lot was a 20in Aztec Vase with Four Faces, made in an edition of 100. Two or three years ago, examples of this edition were selling for £16,000 or £17,000. Last week’s piece, which was estimated at $30,000 (£18,000) sold to a US collector for $134,500 (£81,000).

A print of a sea of umbrellas in the rain has surprised Christie’s experts, who had estimated it would fetch between £3,000 and £5,000, by selling for £51,650 to an American collector. The print, titled Wet Afternoon (pictured), is by Ethel Spowers, an Australian artist who came to London to study in the 1920s, and found her feet making lino-cut prints at the Grosvenor School of Modern Art. By the late 1930s she had ceased to work because of ill health.

The stylised, slightly futuristic prints made by the better-known Grosvenor School artists of the time, Claude Flight, Cyril Power and Sybil Andrews, are highly collectable, with some examples selling for up to £100,000. But Spowers, whose work is rare and mostly found in Australia, has lagged behind. Until this sale, her auction record was a mere £9,000.

Older-generation artists who were once feted by critics but are no longer represented by dealers have a white knight in 26-year-old Megan Piper, whose Piper Gallery launches its first show this week. Piper was working for the art storage and transport firm Momart last year when she was inspired by an exhibition of forgotten artists of the 1960s and 1970s at the Ikon gallery in Birmingham. “I thought, there has to be a space in the commercial market for them,” she says.

Piper launches her project with an exhibition for one of the Ikon artists, Vaughan Grylls, in a temporary pop-up gallery in an old church hall in Dalston, east London, on Thursday. Grylls, 67, had his first show at the Institute of Contemporary Arts in 1970, and later made photo collages that anticipated David Hockney’s work. He has arranged 1,000 photographs to resemble the Second World War German fighter plane that nearly killed him as a child. Future Exhibitions are planned for Paul de Monchaux, 76, Tess Jaray, 73, and Edward Allington, 59.

Dennis Hotz, the publisher of Art Review magazine, is to sell his collection of tribal African carvings in order to invest in contemporary African art. The 25 carvings, of the kind which influenced Picasso and other modern artists more than 100 years ago, are expected to fetch up to £2  million at Christie’s in Paris next month. Contemporary African art is a largely untapped market and is tipped by experts as one to watch.