Who were the "four great masters" in the middle of Qing Dynasty?

Ganjia period was the heyday of iron calligraphy in Qing dynasty, which made a breakthrough in aesthetic orientation and changed the single situation in which Dong and Zhao Shufeng were the patriarchs since Qing dynasty. During this period, there were not only four calligraphers represented by Liu Yong, Liang, and Weng Fanggang, but also a large number of calligraphers, such as Liang Lang, Qian Feng, graceful and elegant, wild and uninhibited Yao Nai. After Gan and Jia, the calligraphy of tiexue became increasingly monotonous, especially the prevalence of pavilion style, which led to its deterioration and left a bad atmosphere.