What characteristic is essential for a successful photogram?

For a photogram to be successful, exposure to light is the essential characteristic. A photogram is a photographic image made without a camera by placing objects directly onto the surface of light-sensitive material and then exposing it to light. The areas of the material that are exposed will react to the light, while those covered by objects will remain unexposed, creating a contrasting image. This fundamental process relies entirely on the proper exposure to light to reveal the shapes and outlines of the objects used, thus making it the cornerstone of creating a photogram.

While color filters, manual focus, and high resolution can enhance photographic results in traditional photography, they are not necessary components for the creation of photograms, where the primary focus is on the interplay of light and shadow created by direct exposure.