*1.3. Conservation and Preservation Methods*

Daguerreotypes are fragile, and Daguerre himself recommended that the plate be protected with a cover glass. About 20 years after their invention, the commercial production of daguerreotypes ceased; there was little effort to preserve them and they became collectors' items. It was not until the twentieth century that archives and art institutions began to collect and preserve daguerreotypes [1]. Many preservation and restoration processes have been tried with varying success. As a result of the variation in the methods of preparation, as well as diverse storage conditions, many daguerreotypes have unique damage requiring tailored cleaning methods. As a result, there is not a single method guaranteed to restore these images. While progress has been made towards a more universal cleaning procedure, these procedures completely depend on the original quality of the surface [5]. There are two general cleaning techniques: chemical cleaning and electrocleaning [1,2]. There are also two common methods in electrocleaning, sometimes referred to as the Wei method and the Barger method [11,12]. The Wei method simply applies a cathodic polarization to the daguerreotype plate in a cleaning solution [11]. The Barger method applies both oxidizing and reducing polarizations to induce anodic and cathodic currents on the daguerreotype, switching between the two throughout the process. It is hoped that by manipulating the surface chemistry, the tarnish will be removed, while the image particles (nano particles of Ag coated with Hg forming an amalgam) will remain intact. Various studies have proven that both methods can help restore the daguerreotype image to some extent. However, as

each daguerreotype is unique in terms of the elemental composition of the tarnish and how deteriorated it is, the methods are not always effective. In some cases, electrocleaning treatments have further damaged the daguerreotype. To remove the tarnish from the surface with electrocleaning methods, adjustments of the potential are made. This potential is biased on the daguerreotype surface, and monitored by a reference electrode, as described below.
