The first American portrait photographer, Robert Cornelius, took up daguerreotypy shortly after it was introduced to the United States in 1839, and continued his practice of the art until 1843. Contemporary reports acclaimed the artistic merit of his portraits, as well as his continual improvement of the daguerreotype process. In conjunction with the first major exhibition of his since the nineteenth century, over half of his daguerreotypes were submitted for analysis by scanning electron microscopy. In the absence of written records left by Cornelius about his working methods, it was hoped that these analyses would provide chemical and microstructural data that could be used to reconstruct his working methods and the changes he made in his practice of daguerreotypy over the years. Not only was it possible to follow his improvements on the daguerreotype process, but it was also possible to assign dates to previously undated or loosely dated daguerreotypes on the basis of microstructural similarities with positively dated Cornelius daguerreotypes.