INVESTIGATION OF A SURFACE TARNISH FOUND ON 19TH-CENTURY DAGUERREOTYPES
LEE ANN DAFFNER, DAN KUSHEL, & JOHN M. MESSINGER
9 CYANIDE IN THE DAGUERREOTYPE PROCESS
The historical literature mentions six procedures in which cyanide was used in the daguerreotype process: electroplating; gilding or gold toning; brightening; fixing; “engraving by Galvanism”; and cleaning. The following is a brief outline of these processes.
Electroplating, galvanizing, or resilvering a daguerreotype plate was a common procedure used to improve the surface properties of the daguerreotype plate by allowing it to be more finely polished. The result was greater detail and deeper shadows in the final image. By 1853 it was a regular practice to plate silver by electrolytic action using a Smee's or Daniell's battery (Barger and White 1991). In this process, an unprepared copper or roll-clad plate is treated by adding a uniform layer of silver on the surface of the plate by electrolytic action. Electroplating was the first procedure in which cyanide may have been introduced in the preparation of the daguerreotype plate: silver was electroplated in the cell in a solution of potassium cyanide. Daguerreotypists were also known to recycle used plates by resilvering using this method.
9.2 GILDING OR GOLD TONING
Gilding or gold toning procedures were thought to improve image stability, image contrast, and resistance to corrosion. One gilding procedure referred to in the 19th-century literature was known as “tinging daguerreotypes” (Napier 1864). A patent for gilding daguerreotypes was taken out on October 26, 1852, by Charles L'Homdieu, a daguerreotypist from Charleston, South Carolina. According to Rinhart and Rinhart (1981), this process employed a solution of hot gold cyanide. Barger and White (1991) indicate the solution was composed of sodium thiosulfate and gold chloride.
The daguerreotypist sometimes immersed the plates in a solution of potassium carbonate and potassium cyanide with “a little alum, borax and some other things” (Rinhart and Rinhart 1981, 188). This procedure may have brightened the highlights by slightly etching them.
Barger and White (1991) note that cyanide solutions were sometimes used in the actual fixing procedures.
9.5 ENGRAVING BY GALVANISM
This was a rare daguerreotype procedure, although oddly it was frequently referred to in the 19th-century electro-metallurgy literature. This procedure created electroplate copies of daguerreotypes using an electrolytic cell and a solution of gold cyanide and potassium cyanide (Napier 1864, 493).
Potassium or sodium cyanide solutions were used to remove tarnish from daguerreotype plates throughout the 19th century and until the 1950s, when thiourea was introduced as a less toxic alternative for removing silver sulfide tarnish from daguerreotypes (Newhall 1961).
9.7 THE USE OF CYANIDE
These are six examples of how cyanide might have been employed by the daguerreotypist, and while other uses may exist, this list illustrates the frequency and ease whereby cyanide could have been used at any stage in the production of daguerreotypes. It is important to keep in mind that the methods of each daguerreotypist could differ greatly from the published literature; basic procedures were adapted to fit individual situations, and variations of these techniques were often employed.