This method is for identifying papers and boards that will tarnish or stain silver or other metallic items. The appearance of the tarnish or stain is reported, together with the distri-bution of the tarnishing or staining. Reducible sulfur activity is a common cause of tarnishing.

Certain types of paper, such as water repellent types and metal coated papers, may require a modification of the test procedure. In most cases, water repellant or metal-coated samples may be tested without wetting the test specimen and by prolonging the time in contact with the silver to at least 24 h. When such sample types are tested, state any modification of the procedure which is used in the report.

The principles involved in this test method might be used to test samples for their staining or corrosion properties with respect to other metals, such as steel, copper, nickel, brass, etc. In such cases, it is necessary to use plates or forms of the particular metal or alloy in question and to make such modifications as may be required for the particular purpose. For example, in the case of metal that would rust, the paper might not be wetted; it could instead be heated in an atmosphere of high humidity.