Bull. U. S. B. F., 1927, Pt. II. (Doc. 1031.) 



Fig. 37.-— Optical effects of glazed tiles, demonstrating their uselessness For these tests. A 

 glazed white; 2, glazed black; 3, unglazed white; 4, unglazed red; 5, unglazed black. B. 

 glazed tiles. 1, white; 2, black; 3, pink; 4, yellow; 5. light green; 6, dark green; 7, red 



