whiteprints

Whiteprints are a class of historical reproducible drawings used in architecture, engineering, and construction, produced by photochemical processes that served as alternatives to blueprints. Unlike blueprints, which are known for white lines on a blue background, whiteprints involve a different tonal balance resulting in copies with a light background and darker lines, or a reversed tonal scheme depending on the variant. They were designed to be inexpensive and quick to reproduce large-format drawings.

Whiteprints became common from the early 20th century through the mid-20th century, alongside other reproduction methods. They were used in offices and on construction sites to duplicate drawings for review, permit applications, and on-site coordination. They coexisted with blueprints on blue paper and with vellum originals, and were gradually displaced by photocopying and digital printing starting in the 1960s onward.

Most whiteprints were made by diazotype systems. The original drawing on tracing vellum was laid onto a sheet coated with a light-sensitive diazo compound and then exposed to ultraviolet light. After development with a chemical fixer or ammonia fumes, the latent image became a visible copy. The process was inexpensive and suitable for large sheets, allowing rapid reproduction, but offered a limited tonal range and sensitivity to light.

Appearance and use vary, but copies generally show crisp line work with legible lettering; line weights are often limited. Archival stability can be an issue, and over time whiteprints may fade or discolor, requiring careful storage away from direct light.

Today whiteprints are largely replaced by digital scans and prints, but many archives, engineering libraries, and construction firms retain historical examples. They are valued by historians for documenting construction practices and building histories and may require specialized handling for digitization and preservation.