Lines or segments of lines that Mondrian added relatively late fluoresce little (remain dark) under ultraviolet light. This is the case with the second horizontal from the bottom and the last two right-hand segments of the bottom horizontal line. Mondrian often widened his vertical lines in New York, making them more similar in width to the horizontals. Along several lines you can see a dark, nonfluorescing strip where Mondrian widened the line. The far left vertical line and the second from the left were widened towards the left. The second vertical from the right was widened toward the right. The bottom horizontal line was widened downward, but this must have been done before this line was extended, since there is no dark strip.