19th century blueprints

[ffutures]

The blueprint process was developed in the 1840s, with the modern black and white process introduced in the 1940s, I think.

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.

Anyone know?

Comments

[ffutures.livejournal.com]

Or I can put in a carbon arc machine, of course. Might be fun. And encourages the adventurers to go snooping at night, when they can run into some different problems to the day (sorry if this sounds like I'm contradicting my earlier post, I've had second thoughts.)