After I received my Associates degree in Electrical Engineering Technology, I got a job as a drafter. I did not learn anything about drafting in college, so I was not very useful to the company that hired me. They only paid me $8 per hour, so I guess they were getting their money’s worth from me being a go-for and doing whatever I was told. They set up a drafting class for all of their newly hired employees and I was selected to attend this class. Back in the 1980s everyone was still using blueprints as engineering documentation. This is before the technology of digital images was available that allowed drawings to sent to plotters that are similar to large laser jet printers. Before the advent of CAD Computer Aided Design, all Engineering drawings were created on vellum paper, which was a thin parchment that was translucent and from this blueprints were made.
Manual drafting takes time and a lot of it is repetitive, so there were two methods available that allowed copying images to cut down on the time. One method was to make a Mylar print and the other was to make a sepia print, which could both be reproduced and allow changes to be made on them, while the original remained intact. Sepia prints normally formed dark brown lines, a brownish pigment the same color that is derived from the ink sac of the common cuttlefish Sepia, on to a translucent background. Having the ability to create a secondary original and make alterations on this drawing saved a lot of time for drafters. The ammonia based blueprint machines were eventually phased out when CAD came along and I was happy when I did not have to smell that anymore.
Written for GC and Sue W Weekly Prompts of the Photo Challenge Sepia.