845. Solar-camera printing is used only as a means of making enlarged pictures and is not adapted for small work, owing to the coarsenees of the results and the slowness of their production. The negative to be used for this purpose should not be so dense as one intended tor contact printing, and in manipulating it all harsh, hard shadows should be remedied. A thin, even - flowing collodion should be used, plenty of exposure given, and rather slow, weak development practised. The negative should not be varnished. There are two forms of solar camera used - one known as the "reflecting" and the other as the '"direct printing." They are composed of an objective, a condenser, and a dark-chamber, in
846. Negatives well adapted to solar enlargements should be full of detail in the shadows, but thin; and should, as seen by transmitted light, be full of detail in the high - lights, and not opaque, but semi-transparent. Time them the same as for contact negatives. Most photographers fail in producing a good solar negative by using their developer too strong, causing a coarse deposit on the high-lights. The proper strength of developer is from twenty to thirty grains to the ounce, with the addition of a little alcohol. Always fix the negatives for solar purposes in a weak solution of cyanide of potassium. It is preferable to hyposulphite of soda. Many do not observe proper care in sizing the figure on the plate, giving much trouble to the printer. Always make a standing figure small, so as to allow plenty of background; more than for a card or cabinet. For bust or vignette heads, make the heads never less than one and a quarter inches in length. A smaller size can be printed, but not always with such good results. As very few varnish negatives without showing lines and spots, it is best to leave solar negatives unvarnished. - W. L. Shoemaker.
A receipt for retouching solar negatives, I give you as follows: Make a varnish of
Oil of Cinnamon,...........................
a few drops.
Varnish the negative on both sides. Then grind by drawing the ball of the finger rapidly over the surface of the negative, from one end to the other, on the negative side, grinding the entire surface. Then grind the back crosswise in the same manner, being careful to move the finger in straight lines, as grinding in circles would spoil it. Then retouch to negative in the usual manner, and you have one that will print better than any contact which a vertical frame, or screen, stands for the reception of the sensi-lazed sheet upon which the image is to be printed. A holder for the negative, reversed vertically, is also provided in front of the sheet. The screen upon which the paper is fastened must be perpendicular to the axis of the lens and facing the middle or centre of the lens. Careful, fine retouching of the negative is not hurtful.
346. The next matter is to prepare the surface upon which the print is to be made. Albumenized and plain paper are used the most largely, but oftentimes canvas and wood are also employed. Whatever the substance may be, it must be sensitized and made ready by a method similar to that already given in the Lessons M and N Canvas is to be used when the picture is to be painted in oil, and wood for engraving. The same guarded care as to dirt and light in the wrong place must be practised, and constant vigilance as to the time of exposure and after manipulations.
print of the same size. If the varnish should grind too coarse use less camphor, or more camphor if too fine. - H. D. "Webster.
To soften hard negatives for enlargement, first remove the iodide from the negative with hyposulphite of soda, wash, and then using a vessel with a large opening, place in it a small quantity of a solution of cyanide of potassium at four per cent., of ordinary water, which pour upon the negative at several intervals until it is brought to the desired tone. Now wash, dry, and varnish it. The cyanide is poured again into the stock-bottle, to be used until exhausted. For negatives that are already weak, the strength of the solution of cyanide may be reduced to from three to two per cent. By this process, whilst preserving all the delicacy of the modelling, one succeeds in obtaining transparencies, by which the negative gains considerably in harmony and softness. You may thus prepare for enlargement negatives of the desired transparency, and, if needs be, upon a plate bearing two negatives, choose the sharper one, which you can treat especially for enlargement, whilst you may leave the other for printing ordinary positives. - M. Darricau.
346. The brightest and most vigorous prints are obtained on the ordinary albumenized paper; and consequently, when the season is favorable and the sky unclouded, preference will be given to this paper for solar printing, when the prints are not to be retouched or colored. But, during the winter season, and the early spring and late autumn months, when the sun's power has diminished in vigor, and is frequently obscured by clouds, it is not advisable to attempt printing on albumen paper, because the exposure will be too long to be convenient, and may frequently have to be interrupted, during which time the paper may have changed its dimensions, and no longer lies flat. In such a case as this another mode of printing has to be pursued. The paper is sensitized the usual way, Out on a strong silver solution for two or three minutes, that is, until it lies perfectly even on the solution, and the corners have settled down. The object in this is to get the paper sufficiently saturated with moisture; and the reason for using a strong silver solution is to coagulate the albumen, and not dissolve it off" from the paper, which a weak solution would do. - Prof. J. Towler.
347. There are two methods of making solar prints. The first is known as the "ordinary, " process, which consists in salting and sensitizing ing the sheet, putting it in the and the washing, toning, fixing, and treating it generally as ordinary prints are treated, full details concerning which are given in Lessons M and N. Albumen paper or plain paper may be used in this way.