CLEANING PRODUCTS:METAL/J EWELRY CLEANERS.

METAL/J EWELRY CLEANERS

Metal cleaners are formulated to remove various types of soils from metal- ware and leave behind a polished finish. Brass and copper (Cu) objects react slowly with environmental air to form compounds that result in a blackened and tarnished finish, which obscures the beauty of the metals. Tarnish, the end result of the oxidation of metal, is the principal type of soil found on most metalware. Metals primarily used for decorative jewelry (e.g., rings, bracelets, necklaces, etc.), including gold (Au), platinum (Pt), and silver (Ag), are also subject to chemicals (e.g., skin acids, sulfur- containing compounds) that create an oxidizing environment and subsequent tarnishing effect. In fact, most gold and silver jewelry items are almost always a mixture of metals. For example, most gold jewelry is alloyed with copper, zinc, nickel (Ni), or silver, and silver is frequently mixed with some copper and zinc, to strengthen the metals to withstand the wear and tear of usage. Platinum usually shows the least effects of oxidation, due to the purity and composition of this metal. Brass is simply a metal alloy composed mostly of copper, with a small inclusive fraction of zinc. As such, metal objects, which nearly all contain some amount of copper, may react with oxygen and sulfur compounds (e.g., hydrogen sulfide) to form CuO and CuS, respectively.

Although there are many techniques used to clean such objects, commercial products are often simple solutions of ammonia within a hydro- gen-based solvent, with the additional inclusion of a very fine and mild abrasive called diatomaceous earth (DE). DE is nearly pure silica, in the form of SiO2, with a very porous characteristic. DE consists of the skeletons of small aquatic unicellular algal organisms called diatoms, which have survived evolutionary processes for approximately 100 million years. Placed in the taxonomic family Bacillariophyceae, the cell walls of these creatures are made of silica. Because silica is more dense than seawater or freshwater, the presence of silica tends to cause diatoms to sink into the water depths. As such, DE is collected from the bottom of ancient lake beds and is currently mined and used for many commercial and industrial purposes. Thus, within metal cleaners, DE acts as an abrasive, and the alkaline ammonia dissolves any greasy residue on the metalware. In addition, the ammonia reacts with the CuO or CuS to form the soluble ammonia complex of copper, which is Cu(NH3)42+. The greasy tarnish residue can then be washed away with clean water and a damp cloth.