Does anyone have any experience with NOT painting Britannia metal parts? I recently read that Britannia will oxidize to a dark gray or black patina that is actually protective of the underlying metal. I usually paint Britannia parts but I’m wondering if some parts (like screws, bolts, metal that on a ship exposed to the elements) would look good or realistic. Or maybe applying vinegar or salt solutions to enhance the patina?
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Patina - Hull plates
- Thread starter Stuart Little
- Start date
- Watchers 11
Copper turns green on buildings way inland from the sea.
Green v. Brown Patina
To explain green copper patina, you have to start with the brown "old penny" color. The brown color that copper acquires jingling around in your pocket or on your model from bare copper plates over time is formed by copper reacting slowly with atmospheric oxygen. The CuO or CuO2 salts have the reddish brown to black-brown appearance. All you need is air and clean copper, but a little palm sweat promotes the reaction. Outside of a dip in a solution of an oxidizer like liver of sulfur, it's a pretty slow reaction. Thus extensive old penny colored copper plate on models is typically only seen on the beauties at the museum.
But you might want green-blue. The green patina is actually a carbonate salt rather than an oxide. Once you form the copper oxides, the copper is more reactive and, in water with sources of carbonic acid like carbon dioxide from the atmosphere dissolved into water, the copper oxides can form copper carbonate hydroxides. That's what gives you the green color. The copper carbonate salts are more commonly referred to as malachite (green) and azurite (blue).
You don't need an ocean to form green copper patina, just copper oxide (an intermediate in the reaction, it can just form in solution), some water, and a carbonate source. The most efficient reactions typically happen in solution and you need a source of hydroxide. You can get the carbonates through atmospheric carbon dioxide dissolved into rain or mist. It is promoted with more acid (carbon dioxide is acidic in pure water) and acid rain really speeds things up. Industrial pollution with sulfuric acid can make the reaction faster and contribute new colored salts.
The ocean works even better. It is a good solution for the reaction, there is plenty of dissolved carbon dioxide, and lots of dissolved calcium carbonate (think shells, corals, etc.). And, with the complex mixture of electrolytes in the ocean, you can get some additional interesting colored salts.
One good reason to use copper is that, outside of extreme conditions, copper carbonates and oxides are pretty good chemical protection for the copper metal. Without a strong acid and/or oxidizer, the reaction is relatively slow and the salt films are pretty stable, unlike rust (iron oxide) that forms much faster, especially in marine environments. Iron and steel were never practical until better coatings/paints were developed.
To explain green copper patina, you have to start with the brown "old penny" color. The brown color that copper acquires jingling around in your pocket or on your model from bare copper plates over time is formed by copper reacting slowly with atmospheric oxygen. The CuO or CuO2 salts have the reddish brown to black-brown appearance. All you need is air and clean copper, but a little palm sweat promotes the reaction. Outside of a dip in a solution of an oxidizer like liver of sulfur, it's a pretty slow reaction. Thus extensive old penny colored copper plate on models is typically only seen on the beauties at the museum.
But you might want green-blue. The green patina is actually a carbonate salt rather than an oxide. Once you form the copper oxides, the copper is more reactive and, in water with sources of carbonic acid like carbon dioxide from the atmosphere dissolved into water, the copper oxides can form copper carbonate hydroxides. That's what gives you the green color. The copper carbonate salts are more commonly referred to as malachite (green) and azurite (blue).
You don't need an ocean to form green copper patina, just copper oxide (an intermediate in the reaction, it can just form in solution), some water, and a carbonate source. The most efficient reactions typically happen in solution and you need a source of hydroxide. You can get the carbonates through atmospheric carbon dioxide dissolved into rain or mist. It is promoted with more acid (carbon dioxide is acidic in pure water) and acid rain really speeds things up. Industrial pollution with sulfuric acid can make the reaction faster and contribute new colored salts.
The ocean works even better. It is a good solution for the reaction, there is plenty of dissolved carbon dioxide, and lots of dissolved calcium carbonate (think shells, corals, etc.). And, with the complex mixture of electrolytes in the ocean, you can get some additional interesting colored salts.
One good reason to use copper is that, outside of extreme conditions, copper carbonates and oxides are pretty good chemical protection for the copper metal. Without a strong acid and/or oxidizer, the reaction is relatively slow and the salt films are pretty stable, unlike rust (iron oxide) that forms much faster, especially in marine environments. Iron and steel were never practical until better coatings/paints were developed.
My penny's worth. Seperate plates "age" over several years. The same effect is obtained using urine (mine at least) and was obtained in a couple of days. (the olfactory effect disappeared also in days). Covering new plates with polyurathane or vanish dulled the shine but kept the coppery look. The copper strips (which I cut into individual plates) remain shiny for many years (so far 13), but I don't like the effect and wouldn't use the again.