Oscura is a Zahner blackened patina on steel that has been developed for interior use. Activated steel surfaces create a mottled and artistic ambiance that varies from sheet to sheet. The primary surface is sealed with a clear coat to mitigate rusting due to the effects of the ambient interior environment.
The iron alloys are not commonly used in the uncoated state. Left to nature’s devices, these alloys will develop a rust oxide which will eventually corrode in entirety. The natural color of the iron alloys, when cleaned of scale and mill oil, is a dark blue-gray.
The steels have a dark blue-gray color, while the heavier carbon alloys of cast iron are almost black. Cast iron has a dark carbon-gray surface, which will weather to black. The wrought iron forms are dark blue-gray in tone. Heating blackens the surface, and subsequent shaping drives the dark tones into the surface. Wrought iron is almost always coated with a thick paint to inhibit corrosion.
Oscura Blackened Steel can be blackened or given colors ranging from dark brown to black. One such method to achieve these tones is by dipping it in a heated chemical bath. This process can develop a deep black oxide over the surface of the steel. Oxides produced by this alkali method are weak and prone to abrasion if not protected with waxes or oils. Protection against corrosion is enhanced slightly, but the base metal characteristics may cause a blackened finish on steel to fail if not continuously maintained in an indoor environment.