试论古代铜镜镜面凸起的成因及其相关问题

通过对古代青铜镜的复制研究发现，古代铜镜镜面凸起的原因，是与镜背的镜钮、浮雕及镜缘等的大小及厚度有关。战国镜的镜钮既小又薄，其镜缘都是横截面较小的镜缘，可直接磨成平面，不致出现铸造缺陷。东汉至六朝之间，其镜钮都较大，为使磨制出的镜面没有铸造缺陷，须将镜面中心少磨削、外围多磨削。这样磨削加工的结果，就形成了镜面凸起。

Trial discussion of cause and related problems about convex of ancient bronze mirrors

The front of ancient bronze mirrors has flat and concave surface.Though the flat ancient bronze mirrors are not as flat as the modern mirrors with macroscopic,its surface was flatter at that time.The convex state of ancient bronze mirrors looks like the surface of moden magnifying glass. With recovering and reproducing ancient bronze mirrors ,it is suggested that some bronze mirrors are convex on the front related to their buttons,sculpture and edge onthe back Ifbutton of a millor is lazgl and theil sauptule is high,it's edge must be thick and front is convex,they are related. All the buttons of Warring States mirrors are thin and small,their edge are concave and small in cross section.The oxide layer of front and back were equal in thickness after mirrors were cast,a flat surface could be obtained by grinding directly,and also no defect appeared.From Eastern Han to Three States,some kinds of mirrors that unearthed to the south of Yangzi River,the larger their buttons are ,the more convex on the front.It is related that the large button with the high sculpture and the thick edge,but the thickness of button ,sculpture,edge and other part of back are so different that the thickness of oxide layer on these different part are not equal.It is suggested that these mirrors were ground as a convex front due to prevention from defect of casting.