Copper blue staining, caused

The powder turns blue if it contains traces of metals or if it is in contact with such metals as iron, copper, zinc, etc. Traces of metals present in powder sometimes cause the formation of blue stains around the metallic particles. A blue coloration appears sometimes at the points where the powder is in contact with metal on the inner surface of cases lined with metal. 

Most people are familiar with discoloration or stains that are a result of problem water in the home. Red and brown stains caused by iron, blue and green stains caused by copper, and white scales caused by magnesium and calcium are found in most homes with problem water. The process of softening water removes the minerals calcium and magnesium that are typically found in potable water. The removal of these elements... 

Sodium silicate treatment in the amount of about 4-15 ppm Si02 is sometimes used by individual owners of buildings in soft-water areas. This treatment reduces red water caused by suspended rust resulting from corrosion of ferrous piping, and it also eUminates blue staining by water that has passed through copper or brass piping. 

Traces of dissolved copper will usually be found in rainwater running off of copper-bearing surfaces. This takes place predominately in urban and industrial areas that are highly polluted with SO,. Such rainwater can cause blue staining on masonry, stonework, etc. 

A little bit of iron powder causes brown black flecks and copper powder green/blue ones. Wood and other organic particles result in dents, holes and craters and a grease stain on the sherd surface in a dry spot. 

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