However, advertising photos do not always have to be used in print, they can be made in the form of large enlargements on paper or films and in this powerful form presented to the public. For this purpose, we use only negative films and in the largest possible formats. Unfortunately, not all dyes are lightfast. Directly falling sun rays destroy them or change their shades after just a few hours. The light from incandescent lamps does not affect dyes, because their radiation contains almost no short waves, so images in not very bright rooms, without direct sunlight, they can last for years without noticeable changes in dyes. Only in the case of too much humidity - the second enemy of dyes - their durability becomes limited. At exhibitions or in display cases, we cannot extend the durability of paintings other than by shielding them from direct sunlight.
The transparencies are illuminated from behind; be careful of the light coming from the front, so that it is not too strong and does not shine brighter than the rear light. The light from fluorescent lamps causes no or almost no discoloration of the pigments that make up the image. Incandescent lamps should be avoided as much as possible due to the significant amount of heat they emit, in addition, fluorescent lamps provide better and more even lighting. Due to the, that at fairs and exhibitions large-sized slides attract the attention of all visitors, some hints should be given to better represent them. Flat color positive films of larger formats are matted from the base side. We can put them between two glass plates, transparent or between one transparent and the other opaque yes, so that the backing side is facing the public. This should be taken into account when making enlargements, so that the image is not reversed later. The membranes should be facing the substrate forward therefore, in order to protect the most light-resistant yellow layer as much as possible from the influence of daylight. The ground side is matted to avoid light reflection. The light is also reflected by the cover glass, so it's better to hang it vertically instead, they are placed slightly inclined forward, however, there should not be too large lamps or bright objects in front of it. Between the fluorescent lamps and the transparency, there should be one more frosted glass at a centimeter distance, to be able to get an even illumination of the image. The distance from the fluorescent lamps to the image should be average 15 cm, and their distance from each other is 10-15 cm. However, fluorescent lamps do not emit heat, showcases should have openings at the top and bottom to ensure air circulation.