| The Cleaning of Paintings: Problems and Potentialities|Helmut Ruhemann Wikipedia
Helmut Ruhemann (b. 1891 – d. 1973) was a German painting conversationalist and restorer, considered the preeminent of his profession during his lifetime. He was born in Berlin and studied at Karlsruhe, Munich and Paris. He was instrumental both in the promotion and utilisation of x-ray as an art historical tool. and was progressive in his efforts to clean old master paintings in a faithful manner that did not impede on original brushstrokes or outlines. He contributed to the progression of both art history and conversation through his making available his detailed notes and photographs. One of his most celebrated restorations is that of Rogier van der Weyden's Saint Luke Drawing the Virgin, a task he undertook with extreme caution, as it pitted him against such luminaries as Max J. Friedlander, who he faced down in his approach, but whom in the end were complimentary towards him.
He left Germany for England in 1933 following a depreciating political climate. He worked as restorer for the National Gallery, London from 1934, and spent part of the war in Wales and at the Tate Gallery from 1939. Ruhemann is especially noted for the copious notes, detailed letters exchanged with other art historians, and many photographs he kept from his restorative undertakings, all of which greatly broaden our understanding of art historical thinking in the early to mid 20th century.