Drying must not be too rapid, or there is a risk of the image leaving the final support, especially in the shadows. Drying too rapidly may also cause a glazing of the image in parts. If the air is very dry and the temperature high, it is well to retard the drying by keeping the print for several hours between moist blotting boards.
When the final transfer is made on any gela tinized support other than paper, the prelim inary soaking in cold water will not require to be longer than 20 minutes, unless a large propor tion of alum has been added to the gelatine.
After drying thoroughly, the print adhering to the final support should separate from the temporary support either spontaneously or by pulling it away gently, provided that the temporary support has been properly waxed. If both supports are flexible, their separation can be effected by drawing them under the edge of a ruler, as in straightening out a paper which has been rolled.
Any wax which may finally adhere to the print may be cleaned off with a tuft of flannel moistened with benzine or petrol.
With care, it is easy to transfer on to the same support several distinct subjects, such as the portraits of the various members of a family ; or, equally, the several elements of the same picture, such as the addition of clouds to a landscape, a background to a portrait, the different parts of a panoramic view, etc., can all be treated in the same manner. These combinations are facilitated by the employment of either a transparent or translucent temporary support.
A carbon print can be glazed, after it is finished, by being re-wetted and dried on glass (§§ 662. Retouching and Colouring. Retouching and colouring should, preferably, be done before the final with the exception of vignettes, which are generally finished in paste after the print is finally completed.
For retouching, it is evident that all water colours may be used, mixed in such a manner that they match the colour of the print. But it is preferable to obtain, from the makers of the carbon tissue, colours prepared from the same pigments as those used in the manufacture of the tissue. Or a still more simple plan may be adopted : the trimmings of the tissue before sensitizing will provide the necessary colour. A cold solution of alum should be applied to the pigmented gelatine with a small brush in order to avoid any spreading of the retouching during the final transfer.
Finally, a light tinting can be applied to the image before the final transfer. This colouring will be seen through the image after it is trans ferred. For this tinting, albumen colours are preferable ; they may be diluted with a solution of alum.
663. Principal Failures in Carbon Printing.. In addition to the failures common to all print ing processes, already considered in § 617, the principal failures in carbon printing, by single or double transfer, and their causes, are the following— The Film of Gelatine Cracks or Splits. The tissue is too dry when unrolled for sensitizing or printing. It should be moistened by being kept for some hours in a cool cellar, or in a cupboard where several dishes of water have been placed.
The Gelatine Dissolves daring Sensitizing. The bath has been too warm, or the tissue has been allowed to remain too long in the bath.
Running of the Gelatine during the Drying after Sensitizing. Due either to drying in too warm a place, or by keeping too long in the sensitizing bath.
Imperfect Adhesion between the Gelatine and the Support during Development. There are several causes of this defect. The tissue may have been soaked too long before transferring, or the margins may not have been protected, or insufficiently protected, by a safe-edge during printing. Further, the gelatine may have be come insoluble through very slow drying after sensitizing, or by being kept too long after sensitizing, or by a general exposure to light.
The Original Paper Support Refuses to Come away in Development. If the edges only come away it is due to over-exposure, and it is advisable to try hotter water, or the addition of ammonia, or placing the print in a solution of ammonium persulphate. If the paper will not come away at all, even at the edges, the tissue has been fogged by general exposure to light.
The Print is too Weak. The cause is insuffi cient exposure in printing.
The Print is too Dark. Over-exposure. Hotter water should be used.
Blisters Appearing during Development. Due to air-bells imprisoned under the film.
The Image Washes Of The causes are the same as those of faulty adherence to the support, or the print may have been transferred too soon, or there has not been sufficient resin in the waxing preparation on the temporary support.
Markings and Reticulation. May be due to sensitizing and drying at too high a temperature, or rough handling with the squeegee, or trans ferring in water which was too hot or too alka line.
Patches of Irregular Density. Mostly caused by the original paper support having been removed too late, and so protecting certain parts of the image from the action of the water.
The Image Comes Away from the Temporary Support during Drying. This is due to insuffi cient resin in the waxing preparation or to the drying having been too rapid.
The Final Support Refuses to Come Away from the Temporary Support. This is probably due to the temporary support not having been waxed ; or the wax may have been removed in places by too much polishing, or the waxing solution may contain too much resin.
The Image is Partly on the Temporary Support and Partly on the Final Support. This is due to the gelatine of the final support not having been sufficiently swollen in water before trans ferring, or having been dissolved in places being immersed in water at too high a tempera ture.
Shiny or Silvery Markings Appearing in the Light Parts of a Print Produced by Double Transfer, after Drying. Due to faulty adhesion of the depressions of the print with the gelatine of the imal support, through excessive swelling of the print before the second transfer.