At the same time, as an art student, Zeng studied German Expressionism, and the preponderance of social upheaval and intensely felt emotion, against a backdrop of social upheaval, had resonance in his own life. In his "Hospital" series, Zeng moved to a theme that included the use of hospital interiors, where he devoted much of the detail to the patients' moods and the power that certain brush stroking techniques could yield. These paintings often hinted at a sadomasochistic relationship in the world with his pale colors and blood colored flesh of the patients. In using these techniques, he shows a somewhat pessimistic view of the world. His expressionist technique shined through in these works further with an extreme expression in the eyes of the characters. Also, the hands of the patients are notably oversized and the joints are much larger as well. The scenes he depicts seem to show patients caught up in seeming hysteria, and the deep red colors show anger of sorts. After 1994, Zeng's work shifted toward his "Mask" series in which his style takes a drastic shift that is considered the second period in his work. Instead of the anger and brutal nature of the hospital series, the Mask series is more apathetic. The scenes are painted from a distance, and have a mask of some sort as the center of focus. The groups are often small or include a single person, and that seems to show that Zeng is touching on personal relationships and the fact that society is filled with false relationships. By using a mask, even if a person is with a group, there is a sense of solitude for the person wearing the mask. He also explores new techniques that include using a palette knife as a paintbrush. This causes the characters to have an even more blurred edge to them, which essentially masks the painting as a whole. The lighting on the paintings are not coming from an obvious source, and the characters seem to be separated from the world around them through an awkward placement in the background. Through the different techniques, the characters seem much more calm than his earlier hospital series. The figures' hands are in fists and also much more realistic and apparent than in the past, and this causes them to seem as though they are controlling an emotion instead of venting anger, etc. The art by Zeng after 1997 becomes much more stylish through the incorporation of new types of backgrounds like the sea. He uses softer colors that are more blended into each other and this makes for a more comfortable viewing experience. Rather than anger or a controlled emotion, these figures are more relaxed and their hands are sometimes in their pockets.