This section is from the book "Amateur Work Magazine Vol6". Also available from Amazon: Amateur Work.
It sometimes happens that a perspective picture is wanted, either for an assembled view, accompanied by a mechanical drawing of the part, or for other reasons, where a skilled artist is not available (and if he was his time would cost too much to warrant its being used), says George F. Summers in the "American Machinist " It is here a camera conies into play as a drafting tool.
We will suppose, for illustration, that bids for a casting are required, where the patterns are furnished, and it is desired to mail the foundry people blue-prints showing the nature of the work.
A photograph can be taken of the pattern and from a negative a blue-print made, and outlined in pencil emphasizing any points to which especial attention is to be called. The print is then dipped in sodium hydrate, or common lye will do very well, when the blue at once turns into pale yellow, leaving the pencil outline standing out in bold relief, as in the sketch.
It is then a small matter to trace, free hand, the outline on tracing-cloth, making a neat, correct picture of the work at a small cost.