Note 97 — Chapter XV · ABOUT MEDALS.

Perhaps: ‘harden’ (see pp. 68 & 70). I am indebted to Prof. Roberts-Austen for the following note: ‘This passage is amplified in the next chapter where the author treats of the hardening of medal dies. He has shown that before working on the coin dies he has made them as soft as possible, but before they could actually be used for striking coins they would need “hardening” & “tempering.” Hardening steel is effected by heating it to bright redness & then quenching it in some fluid which will cool the metal with more or less rapidity, cold water being usually employed for this purpose. Hence in this chapter Cellini states that there must be ten gallons of cold water in which the hot die is quenched, & kept moving (as in modern practice) until it is cold. “Tempering,” on the other hand, to which he alludes here, consists in reducing the hardness of the quenched steel by heating it to a moderate temperature much below redness. Usually the die would be (in modern practice) heated until a straw-coloured film forms on its surface. Probably such a film is contemplated by the author when he indicates the necessity for removing a film, produced at the hardening stage, by polishing with fine oxide of iron.’