Page "History of film" Paragraph 127

There were other variants of the simple iris as well and in these the mask opening or closing in front of the lens had shapes other than circular.

One of the more frequent of these shapes was the opening slit ; a vertical central split appears in the totally black frame, and widens till the whole frame is clear, revealing the scene that is about to start.

Eventually the diagonally opening slit appeared as well, and then there was the diamond-shaped opening iris, as in Poor Little Peppina and Alsace ( 1916 ), rather than the usual circle.

Again, all of these variant forms were very infrequently used, and when they did occur in American films it was usually in the introductory stages.

By 1918 the edges of ordinary circular irises were becoming very fuzzy when they were used in American films.