About PlateAndFilm

Before roll film and digital sensors, a photograph was a physical object made one plate at a time — a sheet of silvered copper fumed with mercury vapor, a pane of glass backed in black to turn a faint negative into a positive, a lacquered iron sheet that made a keepsake sturdy enough to carry in a pocket. Each process left behind its own signature: a mirror-like surface that flips from positive to negative as you tilt it, a ghostly image on black glass, a thin magnetic sheet in a velvet-lined case. PlateAndFilm exists to help collectors, archivists, genealogists, and the simply curious make sense of these processes and the objects they produced.

The site pairs plain-language explainers with a set of small, single-purpose calculators built for the practical questions that come up around historical photography. The Photo Process Identifierwalks through the physical clues — support material, surface, mount, and case — that distinguish a daguerreotype from an ambrotype, tintype, cabinet card, or carte de visite. The Reciprocity & Exposure Calculator and ISO↔EV Converter help translate a metered reading into terms that make sense for a slow, historical emulsion. The Print DPI & Size Calculator is for scanning and archiving plates at a resolution that will actually hold up in print. The Dilution Ratio Calculator and Collodion Ratio Calculatordo the arithmetic behind scaling a documented historical ratio to a batch size — they perform math on ratios you already have from your own reference source; they are not a chemistry guide.

Alongside the calculators, the journal, learn section, and museumcover the history of the medium — the inventors who made it possible, the studio formats that carried it into ordinary parlors, and the timeline from silvered plates to celluloid film. Every museum and learn entry is sourced from Wikipedia and Wikimedia Commons, never AI-generated.

A few things worth stating plainly. PlateAndFilm is independent and not affiliated with any auction house, archive, or conservation body. It is supported by advertising, which is how the tools stay free with no account required. This site covers the history and identification of these processes; it is not a chemistry how-to, does not provide instructions for hazardous procedures, and nothing here should be treated as conservation, appraisal, or safety advice. If a tool looks wrong, or there’s a process you wish we covered, the contact page is the place to say so.