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. — Unique 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 7.5 

 percent silicone solids in a solvent system formulated 

 primarily for spray application. '"■' 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 0.05 

 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. — Unique Gold Ingot for 9.43 dollars 

 issued by Moffat & Co. in San Francisco. 



Potassium cyanide is frequently used for removing 

 tarnish from silver coins, but it is dangerous and 

 not recommended. A method used to clean daguer- 

 reotypes was tried on coins and found to be satis- 

 factory. This cleaning .solution consists of Thiourea 

 (70 grams), phosphoric acid (85 percent, 80 cr). 



Fig. 52. — Five- and 10-Dollar Pieces issuca oy 

 the Cincinnati Mining and Trading Co.. 1849. 



Ultrasonic cleaning was used successfully to clean 

 several steel punches. It was found that any loose 

 material was slowly knocked away by cavitation until 

 only the base metal remained. Caution must be ex- 

 ercised, however, against indiscriminate use of this 

 method for cleaning coins and medals made of 

 bronze or other such inetals for it could damage the 

 objects. 



An electrolytic apparatus was installed in 1958 for 

 cleaning tarnished and corroded coins. In the elec- 

 trolytic cleaning process, by the action of the electric 

 current, the corrosion process is reversed and the 

 metal is redcposited while the intruding ions are 

 displaced into the bath. 



">* US.VM Rfporl, 1962, p. 56. 



'"■' Charles Van Ravenswaav, ".\n Improved Method for 

 the Restoration of Daguerreotypes," Image ( 1956), vol. 5. no. 7, 

 p. 158. This method had been developed at the Missouri 

 Historical .Society and was adopted at the George Eastman 

 House where we learned about its practical application. 



30 



BULLETIN 2 29: CONTRIRUTION.S FROM THF. MUSEUM OF HISTORY .VND TECHNOLOGY 



