What are original drawings or tracings made of transparent paper called?

The term for original drawings or tracings made on transparent paper is vellum. Vellum, traditionally made from animal skin, has been used for centuries as a medium for creating accurate and detailed drawings. In the context of fire inspection and building plans, vellum is valued for its durability and transparency, making it easier to overlay other materials and provide clear representations of designs.

While blueprints, mylar, and film sheets are associated with architectural drawings and plans, they differ in material and application. Blueprints were historically created using a process that produced a blue image on a white background, primarily for duplicating plans. Mylar is a durable plastic sheet used in various applications, including archiving plans, but it is not the original medium for drawings. Film sheets are also used for photographic reproduction of drawings but do not specifically refer to the transparent drawing medium. Thus, vellum is the most accurate term for original transparent tracings in this context.