annealing 退火

牙材講鑄造的時候，提到一個字叫作 "annealing" （退火）
查了一下字典，結果發現有些字典寫的跟牙材裡面教的不一樣~
朗文LDOCE5 定義為
to make metal or glass hard by heating it and then slowly letting it get cold

劍橋 CALD3 定義為
to make metal or glass soft by heating and then cooling it slowly

剛剛好寫相反~
真奇怪！？

看牛津字典 OALD8 ，裡面寫
to heat metal or glass and allow it to cool slowly, in order to make it stronger or softer

看來退火不一定指把金屬變軟。

韋伯字典 Webster's Collegiate 11 寫著
 to heat and then cool (as steel or glass) usually for softening and making less brittle;

看了許多字典，有寫變硬也有寫變軟。看來不能單用這個詞來判斷到底是變軟還是變硬。