Blueprint is a copy of the original drawing that shows how to construct a machine, a building, or another object. The original is called a mechanical drawing. Drafters use special photographic processes to make copies of a mechanical drawing. The copies are called blueprints because the oldest of these processes produces drawings with white lines on a blue background. Over the years, other photographic processes have been developed that create copies with dark lines on a white background. People use the term blueprint, however, to refer to any copy of a mechanical drawing, regardless of the color of the background.
Making a blueprint.
To make a blueprint, the drafter must first make the original drawing on a material that allows light to pass through it, such as tracing paper, tracing cloth, or tracing film. The original drawing is then placed on top of light-sensitive paper and exposed to a bright light. The light passes through the tracing paper, but it does not pass through the lines made by the drafter.
In the traditional blueprint process, after the light-sensitive paper has been exposed to a bright light it is washed in water. The water causes the paper to turn blue wherever it has been exposed to light. The paper directly underneath the drafter’s lines does not turn blue because the lines prevented the light from striking the paper. This process produces a copy that has white lines on a blue background.
Another process used to make copies of a mechanical drawing is called the white print process. In this process, after the light-sensitive paper has been exposed to a bright light it is developed by contact with ammonia fumes. The white print process creates copies that have dark blue, black, or red lines on a white background.
Using a blueprint.
Blueprints are usually prepared by architects, engineers, designers, and drafters for the guidance of workers. The blueprint provides each worker with important information about the dimensions and position of each piece needed for a project. A machinist making a bumper, for example, will look at the blueprint of the bumper to determine the correct size of the piece of aluminum. A construction worker preparing to pour a concrete foundation will look at a blueprint to determine the proper thickness of the foundation. Both the machinist and the construction worker are reading the blueprint–that is, they are interpreting the views, the dimensions, and the lines and symbols in the drawing. This skill enables workers to understand the detailed instructions that are provided by the designers.
In the past, drafters had to make all mechanical drawings by hand. Today, however, many drafters use special computer programs to create mechanical drawings. As a result, traditional blueprints are no longer as widely used. A large number of designers now store their drawings in a computer and use a printer to produce copies. They can also transfer the drawings directly to other computers for viewing on a screen.
