What is photogram? A photogram is a picture that is not made by a camera or a lenses. to make a photogram you will need to have a light, a red light filter and objects that light can't get through and wait for about 8 seconds for the first try and then the next time you can wait for a few more of less seconds its really up to you.
here a example below.
This one was used by a few objects placed on top of light sensitive paper. That paper has little bit of silver on it and when the light get on the silver the silver turns black and thats is why the background is black and the white parts of the pictures are the parts that the light can't get to so thats its come out so nice and cool.