To preserve the patina, the part should be top coated to prevent air from reaching the metal (see topic). (8) Oxidation will continue to occur over time if exposed to the air. (7) Once dry you can manipulate the result if desired (sand, scrape, steel wool, etc.). (6) The new patina is delicate, allow to air dry for at least 24 hours before handling. (5) Monitor your part, add additional salt mist to achieve the desired result. (4) The material should not be touching the ammonia, the reaction comes from the vapors. (3) Seal your part in a clear airtight container, suspending the part over liquid ammonia. (2) Sprinkle some dry salt grains on top (optional). The key with this method is to spray the material with a salt solution mist (avoid rubbing it on). (1) Mix a solution of saltwater in a spray bottle, adding as much salt as the water can dissolve. Make sure that the part is clean and free of surface oxidation I use 0000 steel wool to polish the material before application. Gather all your materials before you begin. This method tends to produce a unique outcome each time, resulting in a mix of colors and patterns. The three (3) main compounds that are responsible for the later stages of green / blue patina are Brochantite, Malachite, and Azurite. The timing and color composition depend on the location and atmospheric conditions (ratios of sulfur, water, sodium chloride, carbon dioxide, oxygen, etc.). The colors range from a shiny pinkish red, to brown, black, and eventually to different shades of blue, purple, and green. Although these reactions have all kinds of fancy names like copper oxide, copper dioxide, copper sulfide, copper carbonate, etc., the interesting part is the dramatic change in color throughout the process. The Statue of Liberty was not always green - through a series of complex reactions, it took over 30 years for her to evolve into her current appearance. It is also referred to as a ‘passive layer’ which protects the statue from further oxidation. This final stage of oxidation is referred to as verdigris, which means ‘Green of Greece’ in Old French. Since most of us are under the age of 100, we think of the statue in its current color, a pale blueish green. Probably the most famous example of copper oxidation is the Statue of Liberty, gifted to the United States by France in 1885.
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