DRY PLATES (Fr., Plaques seches ; Ger., Trockenplallen) Sheets of glass of given sizes coated with gela tine emulsions. The term arose in the early days to differentiate them from wet collodion plates. The introduction of the gelatine dry plate marked a new epoch in photography. There is some difference of opinion as to who was the actual inventor, Burgess, Maddox, Kennett, Wratten, and others all working at the same time in practically the same direction. It was, however, on September 8, 1871, when Dr. Maddox published an account of his experi ments, that the first hint was given. On July 18, 1873, J. Burgess, of Peckham, advertised and sold ready-made emulsion with which photographers could coat glass and so make their own dry plates ; Kennett followed, and on November zo of the same year took out a patent for his " pellicle," with which photo graphers could make their own plates. Improve ments followed rapidly, Bolton, Sayce, Wratten, Mawdsley, Berkeley, Abney, Bennett, and others doing much to bring the dry plate to per fection and to make it an article of commerce. As far as can be ascertained, the first ready-made dry plates were advertised in April, 1878, by Wratten and Wainwright and the Liverpool Dry-plate Company (Peter Mawdsley), the plates by the latter firm being called the " Bennett Plates," and the price for quarter-plates being 3s. per dozen. It was not until 188o that gela
tine dry plates became really popular.
In process work, considerable progress has been made of late years in the use of dry plates. Excellent commercial dry plates, specially made for line, half-tone, or colour work, are now obtainable. The methods of handling are not very different from those in ordinary photo graphic work, except that greater care has to be taken to avoid over- or underexposure and fog ; the lines mist be kept perfectly clear and sharp, and in half-tone work great care and skill have to be exercised to obtain sharp dense dots of the right size and quality. In this respect dry plates are more difficult to handle than wet collodion. Backing is found to be an advan tage ; the negatives usually have to be cleared with ferricyanide and " hypo " (Howard Farmer's reducer) ; and intensification, preferably with silver cyanide, is generally necessary. For the making of dry plates, see " Coating," " Emul sion," etc. For the various manipulations, see "Exposure," "Developing," "Fixing," " Ton ing," " Washing," etc.