The methods of vignetting given above do not give the best effects with bromide and gas light paper, although some commercial vignettes allow of printing to be performed by artificial light almost as easily as by diffused daylight. For vignetting bromide prints or enlargements the vignetter must be moved while the exposure is being made, cut-out cards being used. A card is cut of the desired shape and size, the latter being sufficient to prevent the light creeping round the sides and causing fog in the case of enlargements. The card is held between the sensitive paper and the lens, and moved back wards and forwards in order to spread the light.
The nearer the lens the greater the diffusion, and the more of the image upon the paper. Contact bromide and gaslight prints are vignetted in the same way, except, of course, that the bromide paper is placed in a frame with the negative in the usual way and the vignetter held between the frame and the source of light. The hole in the card must be small in comparison with the size of the vignette desired, as the light spreads considerably ; it is also advisable to arrange the light so that the print or enlargement takes some little time to expose, in order to give more time for effective vignetting.
In process work, half-tones are vignetted by special means. Holt's vignetter is a triangular frame supporting at its apex a clockwork move ment which gives an eccentric motion to a serrated white cardboard frame, placed some distance in front of the copy and illuminated by arc lamps on the side towards the lens. The frame is set in motion during the exposure, and the effect is a darkening of the negative towards the margins. Mole's vignetter acts by chamfering the edges of the half-tone plates from underneath. A revolving cutter projects slightly through a slot in the table, and the back of the plate is pressed over it at the parts where the cutting down has to be done. The edges of the plate are then beaten down with a fibre mallet, so that they are lower than the central part ; thus when the plate is mounted the edges are below the type height and print lighter.