n. (abbr. PAT)a standard procedure to check for potential chemical reactions between materials used to make enclosures and photographs stored in those enclosuresISO 18916, 2007ISO 18916:2007 evaluates possible chemical interactions between enclosures with processed silver-gelatin, colour (dye-gelatin), inkjet prints made with dye-based and pigment-based inks, thermal dye diffusion transfer (“dye sub”) prints, digitally printed dye-diffusion-transfer prints, liquid- and dry-toner xerographic prints, liquid-toner electrostatic prints, and diazo images after long-term storage. It does not pertain to harmful physical interactions such as blocking (sticking together), dye bleed, adhesive migration, or plasticizer exudation. It does not pertain to important criteria of enclosures such as their inherent chemical stability, physical integrity, and workmanship. Passing the photographic activity test (PAT) does not indicate that a material is archival. This term has no clear definition and is not used in this standard. Photo-safe, storage enclosures and their components are covered in ISO 18902, which includes passing the criteria of the photographic activity test.Ritzenthaler 2010, 211All enclosures and mounting materials used to house or exhibit photographs should pass the Photographic Activity Test (PAT) as specified by the International Organization for Standardization (ISO). This includes the various papers, plastics, and boards that are commercially available, as well as any component elements, such as adhesives, inks, paints, and labels.IPI 2019The Photographic Activity Test, or PAT, is an international standard test (ISO18916) for evaluating photo-storage and display products. Developed by IPI, this test explores interactions between photographic images and the enclosures in which they are stored. The PAT is routinely used to test papers, adhesives, inks, glass and framing components, sleeving materials, labels, photo albums, scrapbooking supplies and embellishments, as well as other materials upon request.Harvey and Mahard 2020, 188The word archival is not a reliable indicator of quality since manufacturers and suppliers are not required to share a universal definition of the word. Instead, look specifically for materials that contain no lignin and have passed the Photographic Activity Test (PAT), which confirms that the paper will not cause fading or staining of photographic materials over time. Suppliers of archival materials will usually indicate when enclosures, boxes, and matboard are lignin-free and have passed the PAT.