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FAQ: Patinas on Copper, Brass, and Bronze
This page is intended for those many readers who ask something like: "I want to put a red (brown, black, green) patina on my copper (brass) statuary (mailboxes, gutters, sun dials)" --
Patinas can probably be classified as of three general types, or a mix of the three:
- Heat coloring,
- Salts of the base metal, obtained by treating the base metal with acid, salt, ammonia, etc.
- Salts of a different metal, obtained by "painting" the object with a store-bought patina solution, or with chemicals can contain other metals.
Many artists like the heat coloring for its subtle rainbow hues and freedom from chemicals. But most of the "colors" produced aren't "real", i.e., actual pigments; rather they are interference coloration similar to the rainbow hues of a drop of oil in a puddle (light bounces off both the top and bottom surface of the extremely thin transparent oxides and oils, causing an 'interference' color). But this brings a limitation in that clearcoating masks the thinness of that layer, and destroys much of the coloration.
Heavy layers of metal salts created by the action of chemicals on the base metal, or by painting other metal salts onto the surface, can make more durable colors, but they tend to be more solid than rainbow-like in appearance, and they do require the use of chemicals.
Related threads already posted
Patina questions have been the topic of almost countless letters here. You can search the site with your desired terms, or see this small sampling for starters:
Letter 790, "How to antique copper",
Letter 838, "Looking for Formula for Rust Patina",
Letter 982, "Gunsmith Blueing / Hot Bluing of Firearms",
Letter 1198, "How to Darken Copper, Brass or Bronze",
Letter 1215, "How to Antique or Blacken Gold rings and jewelry",
Letter 1783, "Antiquing a new chrome finish",
Letter 2378, "Ingredients in Rust Patina?",
Letter 2433, "Clear Finishing Dilemma",
Letter 2526, "In search of copper patinas",
Letter 2662, "Preserving heat coloring of copper when clear coating",
Letter 2850, "Protection for outdoor sculpture with rust and patinas",
Letter 3055, "How to patina brass".
Additional resources on line
But if you have a serious interest in patinating. . . There are hundreds of different colors of patinas possible and it is impossible to verbally describe them. So you may want to borrow from your library or buy: The Colouring, Bronzing, and Patination of Metals by Richard Hughes, and Michael Rowe--which contains 200+ color plates and a thousand formulas.