When performing maintenance on your metal mouldings, the most important thing to consider is the type of metal you’re working with.
Different metals require different levels of care and cleaning methods. Some chemicals in commercial cleaners can seriously damage a beautiful moulding.
However, some metals don’t need to be polished, cleaned, or cared for much at all, and can survive with a wipe down every now and then.
It's also important to understand how to protect your metal mouldings not only from natural elements, but from other metals as well. Below, we’ll explain the best ways to shield different metals from corrosion.
But before discussing specific metal care, let’s go over some general must-know information about decorative metal.
General Metal Mouldings Information
Anode (+): a positively charged metal.
Cathode (-): a negatively charged metal.
Galvanic Compatibility Chart: Lists metals in order of anodic index (measured in Volts). At the top is gold, with a low anodic index of 0.00 V. At the bottom is beryllium with 1.85 V.
|Metallurgical Category||Anodic Index (V)|
|Gold, solid and plated, Gold-platinum alloy||0.00|
|Rhodium plated on silver-plated copper||0.05|
|Silver, solid or plated; monel metal. High nickel-copper alloys||0.15|
|Nickel, solid or plated, titanium alloys, monel||0.30|
|Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys||0.35|
|Brass and bronzes||0.40|
|High brasses and bronzes||0.45|
|18% chromium type corrosion-resistant steels||0.50|
|Chromium plated; tin plated; 12% chromium type corrosion-resistant steels||0.60|
|Tin-plate; tin-lead solder||0.65|
|Lead, solid or plated; high lead alloys||0.70|
|Aluminum, wrought alloys of the 2000 Series||0.75|
|Iron, wrought, gray or malleable, plain carbon and low alloys steels||0.85|
|Aluminum, wrought alloys other than 2000 Series aluminum, cast alloys of silicon type||0.90|
|Aluminum, cast alloys other than silicon type, cadmium, plated and chromate||0.95|
|Hot-dip-zinc plate; galvanized steel||1.20|
|Zinc, wrought; zinc-base die-casting alloys; zinc plated||1.25|
|Magnesium & magnesium-base alloys, cast or wrought||1.75|
Dissimilar Metals: Metals that are far apart on the anodic index chart. For best results with your indoor metal mouldings, we suggest not layering metals that are more than .25 V apart. For outdoor mouldings, metals should be no more than .15 V apart.
Electrolyte: A liquid or gel that contains ions and can carry a charge (e.g. water, humidity, condensation). Electrolytes act as the vehicle for galvanic corrosion between dissimilar metals.
Galvanic Corrosion: Caused by dissimilar metals coming into contact in the presence of an electrolyte. This corrosion happens when metal ions scoot from the anodic metal to the cathodic metal via the electrolyte, causing corrosion or oxidation (think of the ions as people moving from a crowded room to an empty one).
In short: dissimilar metals should not come into direct contact with each other.
In cases where contact is necessary or unavoidable, corrosion can be prevented by plating or coating the cathodic metal with an anodic metal (like putting security guards in front of the empty room so people can’t leave the crowded one).
This metal coating is morbidly known as the sacrificial anode. The most common example of a coated metal is galvanized steel; zinc is applied to raw carbon steel as a shield against the elements. The zinc will corrode first, leaving the steel underneath strong and completely intact (at least until the zinc is gone).
Roll formed aluminum is manufactured raw with natural imperfections.
If those imperfections don’t work with your design, you can easily sand them out. We recommend using fine sandpaper or Scotchbrite pads, and keeping the sanding tools wet to reduce dust and residue.
The only cleaning solution you need for aluminum is good old soap and water.
Aluminum can easily withstand the elements due to its ability to self-passivate. This means aluminum will form its own thin (but effective) oxide shield-layer to prevent further harmful oxidation. It corrodes itself to prevent even worse corrosion. Pretty neat!
Aluminum oxide adheres strongly to its parent metal, unlike many oxides on other metals. It also repairs itself immediately if damaged.
Overall, aluminum doesn’t need a lot of special treatment or care. It’s a great all-purpose metal.
Aluminum can be custom-colored via anodizing. Anodizing thickens the naturally-occurring oxide layer on the metal, which can be tinted during the process.
Anodizing kits are available for purchase, but the required acids and special handling make DIY methods imperfect. Most anodizing is done in large scale industrial facilities prior to fabrication or installation.
Copper, Brass, Bronze, and Other Red Metals
(Photo courtesy Jack Gruszka of Full Spectrum Interiors Corp. -- Mountain Ridge Country Club in West Caldwell, N.J.)
We recommend simple polishes with fine whitening or precipitated chalk.
DO NOT use abrasive papers, steel wool, or bronze wool - these will abrade the surface, causing deeper oxidation and shortening the life of the metal.
Soap and water is the best option for cleaning your red metals. Commercial cleaners tend to cause more problems than they solve.
DO NOT use the old baking soda and lemon juice/vinegar treatment. The chlorides and salt will complicate any future cleanings and may damage your metals.
Red metals are known for their beautiful aged patina, which is the result of oxidation. We recommend allowing your red metals to age naturally, though some people do prefer a clean, polished finish.
If you want your metal to stay shiny, wax is the best means of protecting red metals from oxidation. A fine coating of microcrystalline wax is easy to put on and take off as needed.
We DO NOT recommend using lacquer - if it gets scratched, lacquer must be removed with special strippers. This process is difficult, toxic, and damaging to your mouldings.
However, if you absolutely need to use lacquer, synthetic is the best choice. Incralac is a tried-and-true brand that can be found at antique preservation suppliers.
Commercial Steel Mouldings
Cleaning steel is as simple as rinsing the metal and wiping it completely dry with a soft cloth. If harder scrubbing is required, do so carefully with a plastic bristle brush.
Avoid steel-on-steel (steel wool and brushes) unless you’re going for a brushed texture.
When cleaning galvanized steel, the key is a soft touch. Rough cleaning can remove the protective coating (the important part).
Galvanized Steel Mouldings
Galvanized steel has a zinc coating that protects against corrosion. This coating comes in two standard finishes.
Matte - Matte-finish galvanized steel is typically called Galvannealed or Electro-Zinc coated steel. Matte-finish steels are good for painting, because their texture allows for a strong bond between the surface and paint.
Spangled - Spangled-finish is achieved through hot-dip galvanization; it is very shiny, classy, and industrial. This coating does not bond to paint very well, unless special primers are used.
Uncoated Carbon Steel Mouldings
If you prefer the look of uncoated steels, linseed oil will be your go-to rust protector.
Linseed oil has been used as a metal finish and rust protector for centuries. You only need a thin coat on your metal mouldings - a thick coat will not dry properly and will become a mess.
You can also let your uncoated steel rust in a controlled environment for an artistic oxidized look. If you control the humidity and temperature of its environment, the metal will age very slowly and become quite beautiful.
After the metal has oxidized, linseed oil can be applied to protect it from further oxidation.
Keep Metal Mouldings at Their Best
Metal mouldings not only provide a pleasing aesthetic, they also improve the durability of your work. Depending on the project at hand, you have the ability to choose your metals so they best fit your preferred level of care.
To keep your metal mouldings at their newest, strongest, and most beautiful, make sure you perform proper care and maintenance.
If you have any other questions about metal moulding care and treatment, we are happy to provide answers.
(Editor's note: This article was originally published in January 2016 and was recently updated.)
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