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.
Quality Of Negative. The printing quality of the negative required for this paper is practically the same as for Aristo Platino or matte papers, generally. Bear in mind, however, that a strong, harsh or contrasty negative will not give the best of results. A negative should be fully timed, fully developed, retaining snap and brilliancy. Over-exposure and extreme over-development causes hard, chalky whites and generally unsatisfactory results. The tone produced on this paper is largely governed by the quality of the negative and the depth of printing.
Masking The Negative. If it is desired to print from a 4x5 negative select a sheet of paper 8x10, 10x12 or 11x14 inches in size, thus providing for a liberal margin around the picture. First, in order to supply this margin it is necessary to have a large printing frame, the size depending upon the size of the sheet of paper employed. This frame must be fitted with a sheet of plain, clear glass. Next secure a sheet of plain, black opaque paper to fully cover the glass, and with a sharp pocket knife, or regular trimming knife, cut an opening in this mask of a suitable size and shape to suit the negative from which the print is to be made - for example, say 3 3/4x5 1/2 inches. Be careful that the edges are perfectly smooth, that the corners are square and the final cut-out is absolutely true. Place this mask on the plain glass and lay the 5x7 negative on the cut-out, adjusting it to the opening, and with gum stickers fasten the negative securely to the mask. After dusting the negative, lay the collodio carbon paper on top of it, backing this paper with a sheet of felt, or two thicknesses of dry blotting paper, then fastening the back of the printing frame as usual. Having the thickness of the negative between the mask and the print will give the necessary blending and overcome the sharp lines which would surely be formed if the mask were between the film of the negative and the paper. It would be a mistake in making prints from 5x7 negatives to allow for less margin than 2 1/2 inches, as the margin adds greatly to the artistic effect of the picture.
Depth Of Printing. Collodio carbon paper is printed practically the same as other printing-out matte papers, but under no circumstances should the paper be under-printed, as rich results can only be obtained through extremely deep printing. Print until the highlights are quite strongly tinted - at least two or three shades darker than you desire them when finished. Too light printing results in weak and flat looking prints. It is, therefore, necessary to print deeply. For experiments with collodio carbon paper it is advisable to print on small pieces of paper, making several prints, varying the depth of the printing. Then wash, tone and fix these test prints, and note when dry which of those toned give the best results. Once arriving at the proper depth to print, full size sheets may be used and the prints masked in the usual manner.