In 1970, Chu saw the exhibition on Rembrandt Harmenszoon van Rijn (1606-1669) at Rijksmuseum in Amsterdam, Netherlands. He was deeply attracted by how Rembrandt could trigger various emotions in the viewers just by his depiction of lights and shadows. As such, Chu started spending more time on mastering skills of portraying lights and shadows to veil his painting with a bit of mystery. In 1972, during his travels in Germany, he delved into the techniques of expressionism in Berlin. There, he was inspired to express his feelings more directly on the canvas. The unrestricted strokes in Chu's precisely arranged composition become smooth and gorgeous, making these works more powerful.

In his 1970 works, the overall tone was brighter, and colors dazzled in the dark background. In Untitled for example, the upper half to the center of the composition is in orange-red and black. And Chu diluted the oil paint so that it is no longer gluey, but washes through the canvas as does ink wash. Like the careful composition in the upper half, the light texture reminds the viewers of ink wash, making the painting intense and mysterious. In this way, the direct impact of his early abstract paintings has become the fury covered by colors, just like the invisible force behind such natural phenomena as water splashing, wind blowing, and things growing. Chu created relatively fewer works in the 1970s, making Untitled particularly valuable.