From October 1948, after the death of his mother, Rothko started using symmetrical rectangular blocks of two to three opposing or contrasting, yet complementary, colors. Also, for the next seven years, Rothko painted in oil only on large canvases with vertical formats. Very large-scale designs were used to overwhelm the viewer, or to make the viewer feel "enveloped within" the painting. For some critics, the large size was an attempt to make up for a lack of substance. In retaliation, Rothko stated: