Kenneth B. answered 09/19/16
Photography and writing tutor
To begin, you must understand that daguerreotypes have an aproximate ISO speed of 0.05. and are sensitive to a fairly narrow band of the light spectrum (mostly blue range). This means that even in full sunlight an exposure can take more than 4 seconds. This had several effects on early portraiture, first, it could really only be practiced outdoors, or in specialized rooms which had large windows to allow lots of sunlight in. Second, poses had to be selected which would allow the model to hold perfectly still for an exended period of time. Portrait chairs of the time were made with a thin arm extending up from the back which had an adjustable brace to hold the neck and head in place. Any movement would impact the sharpness of the photograph in that area, so fine lace or embroidery was often lost as a detail, however this could also provide softer details in the face. One final note, because these were direct positive processes, any writing which was to appear in the photo had to be mirrored on set, as a result many photographers carried special props on which all the writing was backwards, so it would appear properly in the photo.