MODE OF COPYING THEM BY THE TITHONOTYPE. 



it will bear on its surface a complete impression of the drawing, all the details being 

 given with inexpressible beauty, the minutest lines and dots being present. 



758. From the same plate a series of these impressions may be taken. The images 

 that are on them may be seen either by reflected or transmitted light ; in the former in- 

 stance, most favourably by placing them on black velvet. 



759. I have hopes of improving this method so as to introduce it into effectual use. 

 The practical difficulties that are in the way rest in the circumstance that the isinglass 

 often spills off in chips instead of separating in one unbroken sheet. And the plate 

 from which the impressions are taken, or with which the printing process is carrying 

 on, becomes injured ; not by having its surface removed, but by the isinglass adhering 

 in circumscribed places, and obstinately refusing to detach itself. 



760. This refinement on the art of printing, or, rather, of casting, might be supposed 

 to give rise to very perishable results. This, however, is far from the case ; I have 

 now by me proofs made nearly two years ago, and they do not seetn to have under- 

 gone any change. They have lain loosely in a drawer. 



761. I presume, therefore, that any process which can exhibit the colours of mother- 

 of-pearl will also exhibit Daguerreotype images. This lays open a variety of new 

 branches of the photographic art. 



762. As a name for these processes of copying the surface of a Daguerreotype, I 

 would suggest the word TITHONOTYPE. 



763. To carry this process into effect, the operator proceeds as follows : The Da- 

 guerreotype which he designs to copy is to be covered with a thin film of gold in the 

 usual way, care being taken that the film is neither too thick nor too thin. If it be too 

 thick, the resulting copy is injured, and difficulties are more liable to arise in effecting 

 the separation of the gelatinous coat ; if too thin, the plate itself will suffer injury by- 

 having the figure torn off. 



764. A clear solution of isinglass is next to be prepared ; it must be of such a con- 

 sistency that a drop of it poured on a cold metallic plate will speedily set. Much of 

 the success of the process depends on this solution being properly made. There is a 

 substance in the market which goes under the name of Cooper's isinglass, which I have 

 found much better than any other for these purposes. 



765. The plate is to be arranged horizontally, with its face upward, on some proper 

 support, in the current of hot air that rises from a stove. The isinglass is to be poured 

 on until a stratum about of an inch deep is upon the plate. It is then suffered to 

 dry, the process being conducted so as to occupy two or three hours. When perfectly 

 successful, as soon as the drying is complete, the film of isinglass, now indurated into a 

 tithonotype, splits off, and on being examined either by reflected or transmitted light, will 

 be found to bear a minute copy of the original. 



766. To return for a while to the theory of these images. While thus it is plain 

 that the optical effect depends on surface configuration alone, and does not seem to 

 have any immediate relation to the thickness or thinness of a film, it is very different 

 with the chemical effect on which the whole phenomenon depends. 



767. The Daguerreotype film, which has been under the influence of light, is po- 

 larized throughout its structure previous to mercurialization. 



