Knowledge of the history of photography in terms of various processes and their dates of introduction, styles of image produced such as the carte-de-visite, and the size of images most popular at different times, can also be brought to bear.
These combined factors can usually be combined to allow the dress historian to arrive at a close approximate dating for any given photograph featuring people in clothes.
The 'lozenge' mark used between 18 to certify the patent of the models registered by the UK Patent Office allows the identification of day, month and year of their registration.
This was especially true in the 1840s when men’s clothing offered tightly tailored coats and trousers. What to look for: Single-breasted, semi-fitted coats falling to mid-thigh. Older gentlemen still wore frock coats, but younger conservative men would sometimes do so, as well. Unlike silver items, there is no date letter on silverplate allowing to recognize the date of its manufacture.For silverplate items the patent's date of registered models may be useful for an approximate dating.Scotland's population also rose rapidly, from 2.8 million in 1851 to 4.4 million in 1901.However, Ireland's population decreased sharply, from 8.2 million in 1841 to less than 4.5 million in 1901, mostly due to the Great Famine.