. Bulletin - United States National Museum. Science. different coefficients of expansion of metal and lacquer. The use of low-pressure aerosol sprayers for the application of Krylon lacquer was therefore dis- continued, and experiments were conducted spraying conveniently thinned lacquers with compressed air at about 40 psi. |.-- non-ionic wetting agent (Photoflo, 2 cc), and distilled water (enough to make 1 liter). After cleaning, the coins must be carefully rinsed in running water, followed by a mild soap solution, then rinsed again and finally washed in distilled water.'"' The ion-exch
. Bulletin - United States National Museum. Science. different coefficients of expansion of metal and lacquer. The use of low-pressure aerosol sprayers for the application of Krylon lacquer was therefore dis- continued, and experiments were conducted spraying conveniently thinned lacquers with compressed air at about 40 psi. |.-- non-ionic wetting agent (Photoflo, 2 cc), and distilled water (enough to make 1 liter). After cleaning, the coins must be carefully rinsed in running water, followed by a mild soap solution, then rinsed again and finally washed in distilled water.'"' The ion-exchange process has been used on a large number of communion tokens made of lead that were encrusted with carbonate. "Rexyn RG 50 (H)" of the Fisher Scientific Company was first used experi- mentally by the Division of Numismatics in 1960. After treatment the tokens were given a protective coating of wax. Fig. 50.âUnique 10-Dollar Gold Piece issued by Templeton Reid in California, 1849. Through the cooperation of the Union Carbide Corporation, the opportunity was given the Di\ision of Numismatics to test a new and promising method of protecting silver coins against corrosion. The prod- uct tested is a low-viscosity solution containing percent silicone solids in a solvent system formulated primarily for spray application.'"â ' The results were satisfactory mainly for protecting bright, brilliant objects. Matt surfaces, especially of bronze medals and coins, should not be coated using this or any other product currently a\-ailable becavise of the re- sulting "wet" appearance. The coating obtained was absolutely clear and no more than approximately mils thick. The protective film may hi- readily re- moved wdth acetone, butyl Cellosolvc, methylene chloride, or other similar solvents. ^ p!^ 7^^ae Fig. 51.âUnique Gold Ingot for dollars issued by Moffat & Co. in San Francisco. Potassium cyanide is frequently used for removing tarnish from sil
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