Aperture cards also known as image cards, consist of single 35 mm film frames mounted onto cards. This format is often used for reproduction of architectural or engineering drawings. This is the preferred type for archival filming as it has excellent image and base stability when correctly processed. It will produce high resolution images and a good tonal range. The image is black and white.
Diazo film incorporates light sensitive diazonium salts in an emulsion.
The image is usually deep blue to black and white, with medium to high resolution and available in all formats. The resilient outer surface of this film is less susceptible to scratching than silver halide film, making it very suitable for reference copies. However, it is chemically less stable and not suitable for long-term retention. Vesicular film uses diazonium salts but the image is produced by tiny bubbles formed in a polymer layer when the film is exposed to ultraviolet light. The film is heat-processed making it popular for quick and easy client copies.