 Rendall became a friend of the writer George Mackay Brown, whom he encouraged, and who had appreciated the quality of his best poetry, having been introduced to him by Ernest Marwick Brown was encouraged by Rendall's visits when he was confined to Eastbank Sanatorium.In 1956 Rendall published "Mollusca Orcadensia", a paper which brings together from all available sources records of marine mollusca indigenous to Orkney, which he had commenced in 1916.He published "Orkney Shore", a work on the seashore life of Orkney, in 1960.