A lap dissolve (sometimes called a cross-fade, mix or simply a dissolve) is a technical term in film editing, most often used in the United States, applying to the process whereby the fading last shot of a preceding scene is superimposed over the emerging first shot (fade in) of the next scene, so that, for a few moments, both shots are seen simultaneously. Generally, but not always, the use of a dissolve is held to indicate that a period of time has passed between the two scenes.
Although in early silent cinema this procedure was created 'in the camera', with the film roll being rewound for the second exposure, it has long been standard practice to create the effect in the film laboratory in an optical printer.
In narrative terms, the length of the dissolve is dictated by the mood or pacing the director or editor wishes to create. For instance, in the opening sequence of Citizen Kane, the dissolves between the master shots are slow because of the pervading sense of morbidity Welles and his collaborators wished to create. In the "News on the March" (montage) sequence shortly afterwards, however, the dissolves are much shorter as the intention is to create a sense of vitality in the life of the still mysterious lead character and speed in the (supposedly) newsreel sequence.
Dissolves are most common in classic cinema (see continuity editing), but are now less often used. The device began to fall in to disuse as film makers fell under the influence of the French New Wave directors and their innovative use of the jump cut and as the absence of a linear narrative became more common. It is also sometimes held that the effect was best utilised in monochrome cinematography, where gradations of gray are mixed rather than possibly incompatible color tones. The impact of television news reporting may also have resulted in the device losing any pretense of having a contemporary feel.
Lap dissolves are usually kept to a minimum in most films. One reason for this is economic, since a lap dissolve is more time-consuming (and therefore more expensive to shoot, and far more expensive to develop in the lab afterwards) than a simple cut. Another more compelling reason is artistic: lap dissolves tend to be more effective when they are used only occasionally rather than employed throughout a film. For both of these reasons, it is very rare to see a shot which both begins and ends with a lap dissolve. A very rare (and effective) example of this is seen in A Place in the Sun, directed by George Stevens, shortly after the climactic sequence when Montgomery Clift's protagonist has drowned Shelley Winters and is now fleeing.