What's more it must be splattered or dripped. It's a revisionless process similar to the "suspended wrists" of Chinese calligraphy. How to have "brush strokes" without a brush poses the greatest immediate difficulty.
加上柏油無法用筆，而是用潑的或滴的，類似書法中的「懸腕」，如何能在無筆的情況下有「筆觸」，是創作之初最困難的地方。