Ambrotypes are Wet plate collodion positives shot over clear glass and seen over a black surface, usually by painting or japanning the glass on its back. Images are typically reversed side-to-side
It is a kind of Wet Plate collodion Positive which appears blue in reflection. The color of the collodion layer’s dense areas is yellow, owing to the iodine, which converts it to a filter for the light, leaving the complementary color to be perceived by the eye. A description of the process and of its chemical basis can be found in this site.
Tintypes are positives made over metal. Most tintypes are wet plate collodion works, as those in this section. No longer tin or iron, are mainly made over black anodized aluminum (aka aluminuntypes)