Type 304. This is a ferrous alloy with increased corrosion resistance due to the addition of chrome and nickel. In order to achieve an optimal corrosion resistance, the Borek frames are etched and subjected to a passivating process as a standard treatment. It is possible, however, that miniscule dirt penetrates the surface. In case where stainless steel furniture is exposed to air that contains chloral fumes or high density of salt, the surface can eventually show corrosion.