The title optical effects were reexamined with models reproduced on the basis of historic knowledge with the same alloy (Sn 22-4, Pb 2-5%, and the rest Cu) and designs of varying thickness, ways of cooling, and also with grinding to an even thickness. Results of physical experiments revealed that local stresses and relaxations as well as a convex bending of the mirror surface caused by the design (including 2 ring-shaped reinforcements) are responsible for the behavior. -- AATA