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.
Note. A good many photographers omit the acetate of soda from the gold bath, claiming just as good results. Whether or not it is best to use acetate of soda depends a great deal on the condition of the water - a matter which every photographer should decide for himself.
Note. The crystal form of acetate of soda is used by many, instead of the saturated solution, the claim being made that the latter loses its strength. One-half ounce of the saturated solution of acetate of soda is equivalent to eighty grains of the crystals.
Carbon-Platino. It is generally conceded that the Carbon-Platino print is the nearest approach to the true carbon of any photographic production. The Carbon-Platino is simply a print on Aristo Platino backed up with platino backing paper. The squeegeeing of the print, necessary in backing up, gives to it a beautiful velvety carbon surface. Carbon-Platinos are usually printed with a narrow white margin and mounted on pliable card stock by tacking the upper edge with glue, leaving the rest of the print free from the mount. To make the glue stick to the collodion back of the print roughen the surface with fine sandpaper. To make Carbon-Platino prints, back up Aristo Platino prints as hereafter directed.
Part II. Backing Prints.
Backing Aristo Platino, Or Any Matte Paper. The object of backing these prints is to make the finished prints lie perfectly flat. This backing paper is made upon the same raw stock, coated with the same collodion emulsion, excepting that it contains no silver and is therefore not sensitive to the light. When prints are backed while drying, the back will draw the same as the face of the picture and the print, therefore, cannot curl or cockle.
Directions For Backing. After the prints have been finally washed, place them one by one, face down on a piece of clean glass and squeegee the excess water from them. On another glass, place the backing paper (which has been previously soaked in water) face down, mop off the surplus water and apply the paste. Mount this backing paper over the print on the glass, being careful to rub it down smoothly from the center toward the margin. The backing paper should be at least one-half inch larger than the print, so when it is mounted over the print on the glass it will leave a margin of one-fourth inch all around the print. This margin of backing paper will adhere directly to the glass, thus holding the print in perfect contact with the glass until it is bone dry. With a sharp knife the print may be cut from the glass and trimmed. The margin of backing paper which remains on the glass may be readily removed with hot water, and the glass made ready for another print.
226. Each glass may be made to do double service by mounting on both sides. First squeegee a wet print on one side of the glass, turn it over and lay on a clean blotter and squeegee a print on the other side. Mount the backing paper over this print; then turn the glass over and mount the backing paper over the print on the other side, placing the glass in a rack to dry. If small prints are made, for instance cabinet size, a dozen or more prints may be squeegeed to one glass. Take a 14x17 glass, perfectly clean on both sides. Place six cabinet prints on one side close together, being careful not to allow any one print to overlap another. Next take a dry blotter full size of glass and lay it over the prints and squeegee in contact; then turn the glass over, laying on a clean blotter, and squeegee six more prints on the other side in exactly the same manner. Then mount a piece of backing paper 12x13 inches in size, over the six prints. This will allow at least one-half inch of margin of backing paper to adhere to the glass around the edges of the prints. Then turn the glass over again and mount a piece of backing paper over the other six prints, and place the glass with the twelve prints mounted on it in a rack to dry.