Why verdigris and not rust?

Solution 1:

Verdigris and Rust are both oxidation, but it depends on the metal which is oxidizing. (as user110518 stated)

verde = (latin) green

gris = (latin) grey (also at black) [ty @all]

rust = (old english) red

https://en.wiktionary.org/wiki/griseus

https://en.oxforddictionaries.com/definition/verdigris

https://www.merriam-webster.com/dictionary/rust

Solution 2:

The definitions linked from the question highlight three main differences between rust and vertigris:

• the metal: iron vs copper, brass, or bronze
• the color: red or orange vs green or bluish
• the composition of the coating: chiefly of ferric hydroxide and ferric oxide vs principally of basic copper sulfate

Solution 3:

Others have already mentioned that verdigris is not caused by an oxidative process. So that is answer enough. But to go further, even if verdigris were caused by an oxidative process:

• According to my Merriam-Webster dictionary (10th ed) the word verdigris has its origins in the 14th century, well before chemical principles of oxidation were understood. So why wasn't verdigris called rust? Because the deposits look entirely different and no one considered them as chemically similar processes.

• Today, it would be misleading (at best) to call verdigris "rust" because rust also carries the connotation of a rust (brownish-red) color.

• Rust is a sub-type of oxidation. Not all oxidation is rust. The term rust is reserved for oxidation of iron-based alloys. Even if the uncited definition in the question comes from a reliable source, and might be technically correct (or jargony) in certain contexts, I doubt that context would extend to everyday descriptions.

Solution 4:

Vert-de-gris would have had a special name because it was of commercial importance. Rust, less so.

In modern technical usage, the term refers to Copper(II) acetate monohydrate ("neutral verdigris") or Basic copper (II) acetate ("blue verdigris" or "green verdigris").

A 19th century (the 3rd French edition published in 1892) book (Traité de chimie industrielle by Johann Rudolf von Wagner) gives some uses that were in use at the time: pigment for oil paints and water color; to make Paris green, for dyeing cloth, and in gelding bronze (specifically, for giving a reddish finish to fire-gelded bronze).

Even at the time of writing, the author notes "verdigris is used much less often than previously, as it has been replaced by copper sulfate in many of its applications."

Going further back, the same substance is listed as a drug in Dioscorides' Materia Medica (1st century AD). The author notes that it's produced in Cyprus, which had mining industry in antiquity. The word "copper" itself comes from the place.

Solution 5:

Verdigris isn't rust because it isn't a product of oxidation. It is a different chemical reaction. The natural stuff is either copper carbonate hydroxide, or dicopper cloride trihydroxide. The artist's pigment is copper acetate.