If you rub too hard, you may damage the piece; too soft, and your efforts will be ineffectual, "according to Sung.
然後待石膏外模脫水、堅硬，而石膏內的水泥浸泡泥塑內模，內模於是軟化脫落；再在石膏外模內灌入樹脂，做成樹脂內模；石膏外模再用水浸泡使之剝落，即可將樹脂模型取出，接合到古物的缺失處。