Drafting through the decades series
Part 3: Copy cat
After inking for the first drawing was done, the engineer of the past could lay back, relax and enjoy a cup of coffee. A big chunk of the work had just been completed.
But what about the rest of the drawings?
This is where reprography would way in. Reprography is the process of reproducing an original design, commonly referred to as the ‘master’. This technique was a common practice among engineers, and had gone through various methods like blueprints, whiteprints and photocopying.
Blueprints are the most recognizable type of reprography. They have been around since the mid-1800s, and the term _blueprint_ is still being used, in an informal manner, to refer to any kind for (floor) plan.
We do have a long history in engineering, but it doesn’t go that far back. In case you are interested in learning more about blueprints, you can start by reading this.
The earliest copying method we had the chance to use were whiteprints.
Whiteprints
Also known as blue-lines. They were actually dye-based prints on an off-white background. Cost-efficient, simpler to reproduce and using fewer toxic chemicals than the blueprints, whiteprints prevailed the engineering world quite quickly. Blue was the most popular linecolor but we mostly used sepia, a dark brownish hue.
The master, the diazo and the fumes
As we’ve already mentioned, the master was drawn on tracing paper, a.k.a. the translucent medium. But in order to produce color you also needed the diazo paper, a commercialized paper coated with a mixture of diazonium salt (a light sensitive chemical) and azo dye (a colorless chemical), which, when combined, produced color.
You had to adjust the intensity of the UV exposure light and the speed of the diazo duplicator to get the desirable outcome.
Both sheets were fed into the machine. In the first chamber the two sheets were exposed to UV light. The exposure phase left you with white areas on the copy wherever there was no lines on the master. Of course the light could not penetrate the lines. This actually brings in mind how the layer masks work in software like Photoshop. During the second phase only the diazo paper went through the machine. Fumes of ammonium hydroxide created the chemical reaction that developed the lines. That distinct scent of ammonia is something that every engineer recalls.
We used to have a duplication room of our own. A low-volume copying machine was there, so that we could create copies whenever needed. It was a Technodiazo by Neolt, equipped with filters that neutralized some of the ammonia scent (or so the manufacturer claimed). Still though; it vividly permeated the air. I do not think that that scent can be erased from our nasal memory, no matter how many years will pass.
Taking care of the copies
The copy unfortunately was not permanent. Within weeks or months it faded away, depending on the amount of the light exposure it underwent. Unless you wanted to lose the design, you really needed to take good care of your copies and store them in the dark. Most of our copies were stored in rolls in the dark and rarely reviewed so we managed to still have some copies that are quite legible!
Document control
Of course changes occurred during a project. Each office had colors of favor the engineers used to markup the various modifications on the copy. Contrasting colors were the top choice because they just made things easier. The standardized color scheme was recorded for reference purposes. After the modifications were finished, the document was crosschecked. The master was modified to include the changes made on the copy. New blue-lines were then printed and this process went on like this until the project was complete.
In our office, yellow, red and blue were the colors of choice for our document review and control. Yellow was used to trace all the correct parts of the whiteprint. Red was for errors, notes, optimizations, alterations to be made, proposals or second thoughts. Following that step, the engineer in charge of addressing the findings, erased the red lines and fixed the problem areas using a blue pencil. If the red marks were too many, the workload was split in half between two engineers.
We actually still use these three colors while reviewing our printed designs. I guess some habits do die hard (if not at all).
What’s next?
Technology moved forward really fast in the 1980s and 1990s. It is no surprise that computers dynamically got in the engineering game during the 1980s. Wanna learn more? Find out in our next article.
