Graduated filters were used in the early twentieth century, for example for darkening skies in landscape photos. One advertised brand was called the "Lifa graduated filters for sky, cloud, and landscape photography. These "sky filters" were not necessarily neutral, since they were used for black-and-white photography, and sometimes used a yellow top half to darken blue skies more. In a discussion at the Royal Photographic Society in 1910, some "debatants" held the use of such "graduated color screens" to be quite limited.