Observing the choice of subject and details which caught Welch’s attention, one can glean his methodology and idiosyncratic approach to attribution in the photos he took of various art collections around the world.
Welch took a connoisseurial approach to the study of painting, and his slide collection contains thousands of photographs focusing on details of brushstrokes, coloration, or background details. These reflect the methods popularized by the historian of Renaissance art Bernard Berenson (1865-1969), whose pioneering work on the authentication of Old Master paintings was based on the close observation of artistic idiosyncrasies. In his essay “On the Rudiments of Connoisseurship,” Berenson explained his view that while a given artist may choose to align himself with a school or style, “…the less necessary the detail in question is for purposes of obvious expression, the less consciously it will be executed, the more likely to become stereotyped, and therefor characteristic.”1
The belief that artists would have personalized ways of painting details such as a human eye, ear, or hand informed many of the attributions that defined Welch’s scholarship. His photographic slides thus serve not only as a meticulous documentation of the paintings he viewed, but as a record of mid-20th century Islamic art scholarship. Such an approach also reflects Welch’s own training. Coming of age in an era before Islamic Art was offered as an academic subject, Welch was largely self-taught. He relied upon visual memory, associations, observations of style, and expertise from trained scholars to corroborate his, at times, literary descriptions of figures, landscapes, and other features in Islamic manuscripts.
 Bernard Berenson, “The Rudiments of Connoisseurship” in The Study and Criticism of Italian Art (London, George Bell and Sons, 1902), 125.