Editing Daguerreotype (section)

=== Plate manufacture ===
The daguerreotype image is formed on a highly polished [[silver]] surface. Usually the silver is a thin layer on a copper substrate, but other metals such as brass can be used for the substrate and daguerreotypes can also be made on solid silver sheets. A surface of very pure silver is preferable, but sterling (92.5% pure) or US coin (90% pure) or even lower grades of silver are functional. In 19th century practice, the usual stock material, [[Sheffield plate]], was produced by a process sometimes called plating by fusion. A sheet of sterling silver was heat-fused onto the top of a thick copper ingot. When the ingot was repeatedly rolled under pressure to produce thin sheets, the relative thicknesses of the two layers of metal remained constant. The alternative was to [[electroplating|electroplate]] a layer of pure silver onto a bare copper sheet. The two technologies were sometimes combined, the Sheffield plate being given a finishing coat of pure silver by electroplating.

In order that the corners of the plate would not tear the buffing material when the plate was polished, the edges of the plate were bent back using patented devices that could also serve as plate holders to avoid touching the surface of the plate during processing.<ref>{{cite web |last=Isenburg |first=Matthew R. |year=2001 |title=The Making of a Daguerreotype |url=http://www.daguerre.org/resource/exhibit/brochure.htm |url-status=live |archive-url=https://web.archive.org/web/20141030100307/http://www.daguerre.org/resource/exhibit/brochure.htm |archive-date=2014-10-30 |access-date=2014-11-12 |publisher=daguerre.org}}</ref><ref>[https://patents.google.com/patent/US10508 Reuben, Knecht. Improved Daguerreotype-plate Holder US 10508 A. Reuben Knecht, assignee. Patent 10,508. 7 February 1854. Print.]</ref>

==== Polishing ====
To optimize the image quality of the end product, the silver side of the plate had to be polished to as nearly perfect a mirror finish as possible. The silver had to be completely free of tarnish or other contamination when it was sensitized, so the daguerreotypist had to perform at least the final portion of the polishing and cleaning operation not too long before use. 

In the 19th century, the polishing was done with a buff covered with hide or velvet, first using [[rotten stone]], then [[jeweler's rouge]], then [[lampblack]]. Originally, the work was entirely manual, but buffing machinery was soon devised to assist. Finally, the surface was swabbed with [[nitric acid]] to burn off any residual organic matter.

==== Sensitization ====
In darkness, or by the light of a [[safelight]], the silver surface was exposed to [[halogen]] fumes to form a silver halide. Originally, only [[iodine]] fumes (from iodine crystals at room temperature) were used, producing a surface coating of [[silver iodide]], but it was soon found that a subsequent exposure to [[bromine]] fumes greatly increased the sensitivity of the [[silver halide]] coating. Exposure to [[chlorine]] fumes, or a combination of bromine and chlorine fumes, could also be used. A final re-fuming with iodine was typical.