I need to know roughly how the original process worked as originally done - I know the chemical principle, what I don't seem to be able to find is a description of how it was actually done. I'm assuming that the plan was clipped over a sheet of sensitised paper and left under a lamp for some time, but beyond that I'm pretty vague on the practicalities. Did they press it under glass? How was it illuminated? Etc. etc.
What I need is the relevant bit of something like a 19th century draughtsman's textbook, or similar. Don't need a huge amount of detail, something like "pressed under glass with a lime-light gas light illuminating the plan" will suffice.