Often a drawing, from which prints have already been made, requires changing. The blueprints then on hand are worthless, requiring more time to correct {537} than it would take to make a new print. An economical way of using the worthless prints is to cancel the drawing already thereon, sensitize the reverse side, and use the paper again.
How To Make Picture Postal Cards And Photographic Letter Heads.
The finished paper keeps several days. Print deep so as to obtain a strong picture and develop in the following bath:
| Distilled water | 3 1/2 fluidounces |
| Potassium oxalate (neutral) | 340 grains |
| Oxalic acid | 4 grains |
After developing the well-washed prints, fix them preferably in the following bath:
| Distilled water | 3 1/2 fluidounces |
| Sodium thiosulphate | 75 grains |
| Gold chloride solution (1 in 100) | 80 minims |
Any other good bath may be employed.
II.—Starch is dissolved in water and the solution is boiled until it forms a thin paste. Carmine powder is added, and the mixture is rapidly and assiduously stirred until it is homogeneous throughout. It is now poured through muslin and spread by means of a suitable pencil on the paper to be sensitized. Let dry, then float it, prepared side down on a solution of potassium chromate, 30 parts in 520 parts of distilled water, being careful to prevent any of the liquid from getting on the back or reverse side. Dry in the dark room, and preserve in darkness. When desired for use lay the negative on the face of the paper, and expose to the full sunlight for 5 or 6 minutes (or about an hour in diffused light). Washing in plenty of water completes the process.
A Simple Emulsion For Mat Or Printing-out Paper.
There will be required, in the first place, 2 half-gallon stoneware crocks with lids. The best shape to employ is a crock with the sides running straight, with no depressed ridge at the top. One of these crocks is for the preparation of the emulsion, the other to receive the emulsion when filtered. An enameled iron saucepan of about 2 gallons capacity will be required in which to stand the crock for preparing the emulsion, and also to remelt the emulsion after it has become set. The following is the formula for the emulsion, which must be prepared and mixed in the order given. Failure will be impossible if these details are scrupulously attended to.