In order to initiate corten steel maturation process, Metalco uses an oxidation process trough weathering. This type of system lends to corten a specific non-uniform aspect and different shades of color are particularly visible in welding areas depending on the fact that in such areas patina process is slower. Shades of colors, indeed, are not a defect.
Corten steel, thanks to the process of maturation/oxidation that characterizes it, is considered a “live” material, which may vary over time, in shades and hues, depending on the shape of the object, the position in which it is installed and according to the cycles of weathering which the object undergoes.

Warning: the average period of “stabilization” of corten maturation process, giving to the material a “testa di moro” (“brown”)
color typical of the oxidized corten, is approximately 12/18 months with adequate weathering.

During this stage of maturation, the corten may leak oxide (“washout”), which may stain surfaces where the products are located. For corten, this is considered a natural and physiological behavior of the material.

To reduce wash-out above, Metalco has developed a specific treatment “ANTI-WASHOUT” the client may request, an extracost will be applied: this treatment does not completely stop the losses, but they will be significantly decreased, and will provide to the product a darker and “refinished” aspect.

For the reasons above, the installation of corten products on fine and/or porous surfaces (e.g. marble, granites, etc.) must be accurately considered, even in case of Anti-washout treatment: in such events it may be recommendable to use, as alternative, the painted steel “corten colored” developed by Metalco.

Also, in the vicinity of the sea, the violent assault of salty air, can lead to the formation of oxides on the surfaces that result in the appearance/colour looking different to normal. This does not affect good mechanical strength of the material.


Appearance/shades of naturally oxidized product at the time of delivery (approximately 2 months of natural oxidation). 1-corten-500x350

Appearance/shades of naturally oxidized product after about 4/6 months of installation.2-corten-500x350

Appearance/shades of the product at the end of the period of oxidation after about 12/18 months of installation.3-corten-500x350

Corten steel with special treatment metalco “Anti-washout””4-corten-500x350Note: the reproduction of the shades shown on paper is only indicative. Upon request, platelet samples can be provided.


You can repair minor surface defects (smears, dents, stains). If the corten is natural/raw (without Antiwashout), rub down the surface with a piece of steel wool ( like Scotch Brite) on the surface, to eliminate the defect. Then, moisten with water and place the product on the outside, until the part returns to the surface characteristics of the rest of the piece.
If the corten is treated with Anti-washout, repeat the previous step, by first removing the treatment left with steel wool (e.g. Scotch Brite). After the area has re-oxidized after exposure to the environment, re-apply with a brush two coats of Anti-washout treatment (purchased from Metalco). If the Anti-washout degrades over time, due to weather or mechanical agents, it is possible to renew the treatment according to the procedure described above (removing residues – oxidation – applying treatment).
After complete maturation (average 12/18 months), corten is considered stable and you can suspend the application of Anti-washout treatment, unless you want to use it in order to revive the surface, making it more shiny and smooth.
In case of any doubt about the proper maintenance procedure, please contact the Metalco Quality Department for advice.

General requirements applicable to all Metalco’s products in any material

Upon receipt of the goods, where it is not possible to place and/or install them within a few days, they must always be removed from plastic (nylon) packaging to allow ventilation and prevent the formation of condensation that can irreparably damage the product. Particularly, the packaging should always be removed immediately if it is not possible to keep the goods in a covered place protected from sunlight.