“Highly cleaned and polished iron is very brilliant,” explained their uncle. “The blade of a new knife, Claire’s scissors, carefully kept in their case, are examples. But, if exposed to damp air, iron tarnishes quickly and covers itself with an earthy and red crust called—”
“Rust,” interposed Claire.
“Yes, it is called rust.”
“The big nails that hold the iron wires where the bell-flowers climb up the garden wall are covered with that red crust,” remarked Jules; and Emile added:
“The old knife I found in the ground is covered with it too.”
“Those large nails and the old knife are encrusted with rust because they have remained for a long time exposed to the air and dampness. Damp air corrodes iron; it becomes incorporated with the metal and makes it unrecognizable. When rusty, iron no longer has the properties that make it so useful to us; it is a kind of red or yellow earth, in which, without looking attentively, it would be impossible to suspect a metal.”
“I can well believe it,” said Jules. “For my part, I should never have taken rust for iron with which air and moisture had become incorporated.”
“Many other metals rust like iron; that is to say, they are converted into earthy matter by contact with damp air. The color of rust varies according to the metal. Iron rust is yellow or red, that of copper is green, lead and zinc white.”
“Then the green rust of old pennies is copper rust,” said Jules.
“The white matter that covers the nozzle of the pump must be lead rust?” queried Claire.