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16 LANTERN-&LIDE MAKING AND EXHIBITING. IN the foregoing instructions it has "Cold" Tones. , been assumed that Metol-hydro- quinone and a cold-tone plate have been employed with a view to the production of a good engraving black slide. As the procedure when a " warm tone " plate and pyro is employed is somewhat different, that method of working will now be described. As a rule, " warm tone " plates are "Warm 1 'Tones. u. i • 1 much slower than those intended for "cold tones," therefore a longer expo- sure will be necessary. The developer should only be mixed when required, and fresh solution used for each plate, otherwise stains and markings will probably appear. With pyro a longer time is usually required for the appearance of the image, and development proceeds more slowly, though this does not apply with equal force to all makes of plates. The appearance of a pyro deve- loped plate as it lies in the developing dish is very deceptive, the image by reflected light being appar- ently feeble and faint. The progress of development can only be followed by holding the plate to the lamp and examining it by transmitted light. A pyro- developed slide rarely looks so dense as one deve- loped with metol-hydrokinone, although in reality it may be more so. The advice previously given as to adding accelerator to assist a nagging developer ap- plies with greater force to pyro than almost any other developer. If good warm tones are desired the exposure must be sufficient to enable a normal developer to bring out the image, and any addition of accelerator, although it may hasten its appearance, will ruin the colour of the slide and spoil its appearance.