Infrared was used a lot before digital came along. When using a printing enlarger it is used more as a tool as opposed to using your film as a stool. An example of infrared photography would be if I didn't put the negative into an enlarger holder for the negative. If I were to print pictures manually and didn't put a negative in the negative sleeve then put a blank piece of paper down and place my hand on top, then turned the enlarger on to expose the light to the paper with my hand over it just for a second. I then send that piece of paper through all the stages of the printing, at the end I would have basically a black background with a with a white hand on it because the white didn't allow light to get to the paper and so its kind of like an x-ray. It looks as if you take an x-ray of your ribs. It is different exposures to light but not used with an actual negative.
