"Corten steel", is a group of aloy steel which were developed to eliminate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years. The corten steel forms a self-protective oxide layer. The anticorrosive properties of weather-resistant steel are based on the protective oxide layer, called patina which forms on the surface of the steel. Under normal weather conditions the patina will form in about 18-36 months, if the surface is alternately wet and dry. At first, the patina is a reddish brown color, but with time takes on a darker hue. The anticorrosive properties of weather resistant steel are better than those of other structural steels in many applications. The steel is self-protecting: the rust layer on the surface becomes a tight oxide layer that slows down the progress of corrosion. The steel is an economical, long-lasting and fully recyclable material.\par \par Warning: The average period where the natural cycle of maturation of corten "stabilizes", giving the material a dark brown shade typical of oxidized corten, is about 12/18 months in the presence of suitable weather conditions. 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.\par \par To reduce the loss of oxide, atech uses a specific treatment which may be requested by the customer, at extra cost: this treatment does not completely block the losses, but decreases significantly the oxide leak, giving the product a darker appearance and "finish." As indicated above, the laying of corten products on valuable and/or porous surfaces (e.g. marble, granite, etc...) must be very carefully evaluated, also in the case of Anti-washout treatment: in these cases it may be advisable to use, alternatively, galvanised and painted steel with the "corten colour". 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.