In his Nature Series, crafted from natural plants, twigs grasses, disused bird habitats and other eye-catching bits collected on his many walks and countryside roaming both in South Africa and England, Rosen explored, experimented and integrated these with diverse media. He used oil, water-colour, and ink combined with aquatint and a soft-ground etching technique which he developed and perfected on his self-designed and built etching press, to produce delicate, decorative and delightful designs.