. Bulletin - United States National Museum. Science. Fig. 52.âFive- and 10-Dollar Pieces issuca oy the Cincinnati Mining and Trading 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.
. Bulletin - United States National Museum. Science. Fig. 52.âFive- and 10-Dollar Pieces issuca oy the Cincinnati Mining and Trading 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. ">* Rfporl, 1962, p. 56. '"â ' 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: FROM THF. MUSEUM OF HISTORY .VND TECHNOLOGY. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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