fred said:
Beautiful answer Mongo.
What are the references of the book?
If 56 is young? ..., I think it's very young....

At 60 I will go to the university of life for studiing "alt processes"...
Fred
The full title of the book is "Primitive Photography : A Guide to Making Cameras, Lenses, and Calotypes". It's by Alan Greene, and the ISBN number is 0240804619. I picked it up based on the description I read on amazon.com; even if you don't intend to start using his processes immediately you'll learn a whole lot about the basic theory behind photography (even though the book itself isn't terribly theoretical; it tends to be more descriptive and only delves into theory when necessary). It's an easy read, and I especially enjoyed the section on lenses (which did lead me to build a few lenses of my own to experiment with).
Amazon's selling it for $21.09, which is a good bargain. The film holders that he describes will only work with the cameras that he describes, but if you were forced to start over from scratch his cameras look very workable and pretty easy to build. (In fact, it would be pretty simple to adapt his camera models to something like foam core board for real experimentation purposes.)
His sections on making paper negatives and contact prints are well illustrated, and he gives a number of formulas for the emulsions depending on your tastes in image tone.
All in all, I think it's one of my most read photogarphic books, even though I've only actually built lenses based on his book. He's basically re-discovered a bunch of very old processes and updated them for modern chemistry and paper, created very workable models for cameras (which are easily scaled to whatever size you wish to use), explained basic lens theories and provided a few simple lens formulas that give surprisingly good results...basically taken the information from the early days of photogarphy and made it available in a useful fashion today. For the price, I think it's an exceptionally valuable book.
(As to what the definition of "old" is...I have no idea. At the age of 45 I still feel young, but I really don't expect to see another 50 years.

)