FERROTYPE PROCESS (Fr., Proctde ferro type; Ger., Ferrotypie) About the middle of the nineteenth century the term " ferrotype " was applied to the process introduced by Robert Hunt as " Energiatype " (which see), but that process was but little used, and the modern ferrotype is quite different.
Ferrotypes (known also as " tintypes ") are pictures taken on sheet-iron plates varnished or enamelled on both sides, the picture side being the more carefully prepared. They are of American origin, having been introduced by J. W. Griswold in 1855, and were also known as " Melainotypes " before the title of ferrotype was generally adopted. It is believed that the earliest reference made to ferrotypes is in Photo graphic Notes, dated January i, 1856, announc mg the invention by a Prof. Smith, of Ohio, of a process of " producing a beautiful picture on a piece of common sheet iron, . . equal to daguerreotypes, and much superior in some respects." The journal calls the pictures " Ferrographs." Ferrotype pictures are positives produced by the wet collodion process, a black or chocolate enamelled iron plate being used as a support for the picture instead of glass. The latter needs backing up with black paper, velvet, or paint. The finished results have the same appearance in both cases, but the ferrotype image is reversed as regards right and left, and the process is there fore not suitable for general application. Every one knows that this process has been widely used for portraiture by itinerant photographers, since by Its aid they can take and finish a por trait in the space of a few minutes. The photo grapher generally takes particular care to arrange the sitter " full face," or in any other position in which reversal is not at first detected. For ferrotype work proper the operator must be within easy reach of his dark-room, as the plates are prepared immediately before exposure.
The process, in brief, is first to prepare the plate with collodion, sensitise in a silver bath, expose while wet, develop with an iron developer, and fix in a solution of potassium cyanide ; all formula' and working details will be found under the heading " Collodion Process (Wet)." The Dry Process.—The introduction of ferro type dry plates has largely displaced the old fashioned wet process ; itinerant photographers use them in conjunction with automatic cameras, which comprise arrangements for developing and fixing, thus obviating the use of the old portable perambulator-like dark-rooms. Ferrotype dry
plates are bought in packets and used like other dry plates, but instead of yielding a negative on glass they give a positive direct upon the black iron or tin support. An example of the developers used for such plates is : Sodium carbonate (pure) 4 >, 200 g.
Sodium sulphite . 2 „ I00 „ Hydroquinone . . i. „ 12.5 „ Potassium bromide . 290 grs. 29 „ " Hypo " fixing solution (as below) . . oz. 25 ccs.
Warm water to . 20 „ i,000 „ Allow to stand for two days and pour off the clear solution for use. In cold weather half the above quantity of bromide is required. After exposure, the ferrotype dry plate is developed until the high lights (which appear brown on a white background) and half-tones are well out, and the plate is then rinsed in water and fixed in a " hypo " fixing solution (sodium hyposulphite 4 oz., water 20 oz.). Development takes from eight to twelve seconds in hot weather, twelve to twenty seconds in a normal temperature, and twenty to sixty seconds in cold weather. After fixing (duration, ten to thirty seconds), the plate is rinsed for a few seconds and dried spontaneously or by gentle heat. It is next varnished, and then gives the appearance of having been pro duced by the wet collodion process. Sediment sometimes appears on the film after washing, particularly when over-developed, and gives the plate a fogged appearance ; it may be removed, before drying, with a pad of cotton wool.
A positive on a ferrotype plate is sometimes used by artists as a means of tracing from. Where a photograph is not to the correct scale a positive enlargement can be more rapidly made than a negative and print. As the image is reversed in relation to right and left, it becomes correct when traced over on gelatine by scratch ing the outline with a needle-point and filling with blacklead or other set-off powder, the gela tine being then turned over and rubbed down on to drawing paper or Bristol board.