This week, New York hosts its Latin American art sales, and tucked away inSotheby’s and Christie’s are two works each by modern sculptors who are being fêted long after their deaths, with their first exhibitions in London for several decades. One is Brazilian artist Sergio Camargo, who was last exhibited in London in 1982, and is being shown by the Lisson Gallery in Marylebone. The other is Cuban sculptor Agustín Cárdenas, whose last London exhibition was in 1962, and is being shown by the Aktis Gallery in St James’s.

In each case, these exhibitions are part of a re-evaluation process for artists who are thought to have been slightly overlooked by the rampant bull market for post-war art. They also underline the way in which dealers are searching, more than ever, to pick up on underrated artists and, as in these two cases, work closely with the artists’ estates where there is a supply of works for sale.

A classic example of this trend has been the American colour-field painter Helen Frankenthaler, who died in 2011, aged 83. Frankenthaler was an important artist in the Fifties and Sixties but suffered neglect in her later years, noticeably in the market place.

However, after her death her estate was taken over by super-dealer Larry Gagosian, and in 2013 he held her first exhibition in New York for 50 years. Now her work is experiencing a revival. At the New York contemporary art sales this month, all six of her paintings offered were sold, mostly above estimates and for more than the artist’s record prior to these sales, the top price being $2.2 million. The highest price during her lifetime was about one third of that.

There are many similarities between the two Latin American artists showing in London. Born within three years of each other, they are both sculptors who began working in wood and/or bronze, went to Paris and were influenced by Jean Arp and Constantin Brancusi, and then discovered marble. But while Cárdenas was embraced by the surrealists, Camargo pursued more abstract forms, associated with the Brazilian constructivists, so formally, they are quite distinct.

Born in 1927, the son of a tailor, Cárdenas did not discover himself artistically until he went to Paris in 1955. In an enlightening catalogue introduction to the Aktis exhibition, Abigail McEwen relates how it was in Paris that he first expressed his Afro-Cuban (as opposed to Hispanic-American) origins through his art and with the encouragement of the ageing apostle of surrealism, André Breton, who welcomed him in to the fold. His work in charred wood from this time embraces the totemic qualities of African and Polynesian sculpture, and is followed by smoother, biomorphic forms in white Italian and black Belgian marble. Critics compared him not only to Arp and Brancusi, but also to Henry Moore and Alberto Giacometti.

The market for Cárdenas’s work has revolved around Paris and the Latin American sales in New York, though in Cuba there is virtually no internal market. He is well represented in museums in Europe and Cuba, but not in America or the UK yet.

At auction, there is a ready market for his work in either wood or marble, large examples of which have sold for up to $250,000 (£160,000). Prices at the exhibition, where several works have already sold, are from £2,000 to £3,000 for works on paper, and between £15,000 and £145,000 for the sculptures.

In Latin America, Brazil has witnessed the greatest surge of interest in its artists, though recently this has been tempered by political and economic events, not to mention the punitive import/export tax rates for its artists.

Born in 1930, Sergio Camargo studied under Lucio Fontana in Brazil, and then finished his studies in Paris. Working in the Fifties with avant-garde artists in Brazil such as Lygia Clark and Mira Schendel, he returned to Paris in the Sixties and represented his country twice at the Venice Biennale.

His earliest and most collectable works are geometric constructions or reliefs made from wood in cuboid and cylindrical form (inspired, he said, by the cutting of an apple). In the past three or four years, prices for these have risen sharply, up to $2.2 million, which was five times the estimate.

His later works in white or black marble have been less sought after, and this is probably where the Lisson show is important. While it does include wood reliefs priced in the hundreds of thousands of dollars, there is more marble work from the Seventies and Eighties represented here with prices starting from just $30,000.