The gallery is planning a major exhibition of the artist's work, opening next autumn.
During his lifetime, Edinburgh-born Cadell sold and gave away most of his paintings within Scotland.
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Hide AdThe children and grand-children of his friends and patrons may still own these works and the gallery hopes to rediscover some hidden masterpieces.
The planned retrospective is the first to be held at a public gallery since a memorial exhibition at the National Gallery of Scotland in 1942. It will consist of around 70 paintings, from public and private collections.
Alice Strang, senior curator, said: "It would be wonderful to bring to light beautiful paintings by this leading artist."