For me, a sculptor is someone who has fully mastered the laws of relief, […] sculpture-in-the-round can only be executed with a view to the relief, and is a composite relief.
Letter from Moissey Kogan to museum director, Max Sauerlandt, 17 January 1922 (SUBH: NSa: 14:05) (translation from German)
Then the fury of producing would seize him: day and night for weeks he would work, turning out figure after figure. Or rather negative molds, hollowed out from blocks of gypsum, from which impressions in clay or bronze casts could be made.
This is an exacting method requiring utter concentration of both concept and execution. Kogan did not want it any other way. Modelling in clay he rejected as too easy and too yielding to temptation; carving and chiselling hurt his feelings.
Dr Karl With, ‘A Revival of Interest. Moissey Kogan’s Work Exhibited Again’ in: Los Angeles Herald Examiner, 8 April 1962