Photographic film is a light sensitive coat atop a material that is flexible and transparent. The first successful base material was made of cellulose nitrate made from purified cotton treated with nitric acid. This made an ideal base material. Cellulose nitrate was used until just after World War II. It has a major flaw in that it will burst into flames at a temperature of about 300°F. Worse, it will continue to burn vigorously even if drenched with water. Likely a movie house, somewhere in the world burned down every day. Thankfully “Safety Film” was introduced in the early 1950’s. It is cellulose acetate which will burn but it will self-extinguish. Today many different plastic film bases are in common use.

Undeveloped photographic is relatively opaque but strong light can travel completely through it. Images of bright object are sometimes spoiled by an unwanted halo that seems to surrounding them. This is called halation. It is light that passed through during the exposure and re-enters the film from the rear. To prevent, a special deposit called an “annihilation coat” is applied to the base film before the light sensitive coat is applied.

Darkroom workers are required to identify the emulsion side (side with light sensitive goodies) and the base side of roll film. When working under a safelight, the emulsion side likely appears dull by reflected light and the base side appears to have a luster. It can be difficult to make this determination especially when working in total darkness. Some tricks of the trade: All roll film tends to curl with an inward twist. The emulsion side is the innermost side.

Sometimes we wet a finger and touch a tiny area at a corner. The emulsion side will feel tacky. Sheet film is individual pre-cut films that we loaded into film holders. These films all had notches on one edge. The notches we could feel in total darkness, they identified the film type. We orientated the sheet till the notches were felt in the upper right corner. Holding the sheets this way, the emulsion side was facing us.

You can identify the emulsion side of developed film by looking at it via light reelected off its shiny surfaces. The emulsion side is dull compared to the base side. You can also look at the edge printing which will be numbers, letters and film manufacturer. These words and numbers read correctly when you are looking at the base side of the film.