While tintypes were invented in 1855, they became widely used to document Civil War battles, encampments, and soldiers, and then later mobile studios appeared at fairs, carnivals, and with traveling photographers.The process was used through the end of the 19th century, but most of the tintypes out there date from 1865-1875.
The process became most popular in period from 1842-1856, but began to wane in the following years.
The complicated process involved polishing a sheet of silver-plated copper, treating it with fumes, and exposing it to a camera to fix the image to the metal -- this resulted in an image that appears to be fixed on to a mirror.
If you have a photo that is cased, has a mirror-like quality where the image changes based on the angle, and the back of it looks like it has some copper and silver elements, you have a daguerrotype, which means likely 1845-1860.
There are ways to date the images inside this range, but for now lets move on to the next type: Ambrotypes.
Ambrotypes are similar to daguerrotypes in that they were often preserved in similar cases, but the difference comes down to the process used and how it looks.
While "dags" were produced on sheets of copper/silver, ambrotypes were produced on an actual mirror that was coated in a silver iodized sulfate solution.This means that the image will be much crisper and appear the same from all angles.Many of the photographers also treated the images with some hand-tinting like the one above.Here's a typical, cased example of an ambrotype from 1859.While daguerrotypes and ambrotypes were generally expensive processes that could only be done in studio, the advent of tintypes brought photography to the masses.Don't let the name fool you: tintypes are actually based on a thin iron-sheet that holds a crisp, black-and-white or chocolate-toned image.