The technique can illustrate emotions ranging from crowdedness, to power, to chaos, or even to movement in a photo.
Color transparencies are an example of positive photography: the range of colors presented in the medium is limited by the tonal range of the original image (dark and light areas correspond).
It is opposed to a negative where colors and luminance are reversed: this is due to the chemical or electrical processes involved in recording the scene.
When film was first made (mid-19th century), it used silver-plated copper sheets that contained three layers with light sensitive chemicals on them.
Other items used to create film included leather, paper, and glass sheets.