This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Formula For Ground-Glass Substitute.
.......................2 1/2 oz.
from 1 1/4 to 1 1/2 ozs.
1104. All the necessary chemicals may be purchased at any drug store.
Caution. Never use this varnish near a naked flame, as it is highly inflammable. Be sure to get benzol and not petroleum benzine.
1107. The ground-glass substitute on the negative gives more strength to the shadows, but at the same time it reduces the printing quality in the white draperies and highlights. If it is desired to print any of these parts stronger, take a piece of cotton cloth dipped in alcohol and proceed to wash off the varnish, or substitute, directly covering the white parts. You will also find that with a sharp knife you can scrape the substitute or varnish, and it is really a cleaner method than using the alcohol. When you have done this, place the negative in the printing frame and cover the frame with two thicknesses of tissue paper, being careful to use French tissue, or onion skin. Ordinary tissue paper has minute holes which would cause black spots on the prints.
1108. Now make a proof, and if you find it does not give the desired results, add one or two more thicknesses of tissue paper and you will be pleasantly surprised to see how much more strength and vigor is imparted to the negative.
1109. If there are only small portions of a negative that you wish to keep back in printing, it is a good plan to apply the substitute on the glass side to these parts which you want to hold back in printing. If it is necessary to hold back the shadows, or strengthen the highlights apply, with a stump or duster, a little blue, yellow or black dry color. The highlights may also be strengthened, by working on this ground-glass substitute with powdered black lead or blue pencil. The blue pencil should be used only where a slight increasing of the highlights is desired. Now, if you desire to increase the strength of the shadows, work over them by rubbing a little vaseline, or gum water, into the ground-glass varnish. This will make the matte appearance more transparent and the shadows will print deeper. The same can be done with the highlights, if they appear too strong.
1110. Still another method of making the highlights print softer, or the shadows deeper, is to melt a little paraf-fine and apply it with a small camel's-hair brush directly to the tissue paper on the places that you wish to print more deeply. The paraffine will make the tissue paper (where applied) absolutely transparent, allowing the draperies to print in harmony with the rest of the print. If convinced that the paraffine has been applied too thickly, scrape it down with a sharp knife.
1111. Paraffine is better than vaseline or oil for this purpose, as they will spread, while the paraffine will not. Remember that wherever doctoring is done it is necessary that the negative be printed under tissue paper.
1112. Often times you will find dirty finger marks on the gelatine side of the negative. These you can readily remove by rubbing with a piece of cotton batting which has been moistened with glycerine. After you have removed the spots, take another piece of cotton and rub perfectly dry the places where the glycerine has been applied. The glycerine acts like a varnish on the negative.
1113. Another very simple method of increasing the density of any portion of a negative is to mix a little dry yellow or orange with one-half ounce of gum Senegal, applying thinly with a camel's-hair brush, moistened with saliva. You will find this will add enough density to the required parts of the negative, without affecting the detail.
1114. In printing landscape negatives you will find that applying a little of this coloring to the sky and portions of the clouds will increase their strength and improve them very much. In printing a group, if part of the faces print too dark, a little rubbing in of light blue or yellow paint on the tissue, directly over these faces, will improve them. For faces that print too white, the tissue paper directly above them should be treated with melted paraffine, which will make the tissue transparent, causing this part of the negative to print faster.
1115. To whiten the sky in landscapes, hold the negatives over a piece of lighted camphor, glass side down. The smoke from the camphor will cause a gathering of soot. Where this soot adheres to the parts of the negative that you desire to print fully - such as trees and buildings - it can be readily removed with a soft cloth or brush. Great care is necessary in handling a negative of this kind, however, as the blackening will rub off quite easily. An excellent plan is to place the negative immediately on a piece of clean, plain glass, binding them together, to protect the blackening.
1116. By the exercise of a little ingenuity the printer can produce many pleasing and artistic effects, oftentimes making good prints from negatives that would otherwise be worthless.