Dissolve enough bichromate of potash In water to color the water a deep orange - or about one tablespoonful to eight gallons of water. Wash the blue-prints in clear water before and after using the solution. Chambersburg, Pa. E. Ray Croft.
Blue-prints are never so over-printed that they cannot be reduced to a suitable tone by a slightly alkaline bath of borax, bicarbonate of soda, washing soda, or ammonia. Blackline, or "ink" process paper, is usually lost if slightly over-printed; if under-printed it develops too gray all over its surface to be of use for tracing or for reproduction photographically. In the winter-time, when prints from thick paper drawings are apt to be under-exposed, I treated a number of such apparently useless prints with a lotion for throat troubles - the first "tonic" available - with excellent results, the invisible lines developing out a strong black on a gray ground. The mixture was tannin-and-glycerine solution to about 20 parts of water. When using this solution it is safer to under-print rather than to over-print, with the resulting weak or broken lines.
Sepia prints, when much over-printed, can be saved by washing in a very weak solution of hyposulphite of soda which bleaches away the image before it can become fixed by the usual preliminary wash in plain water. The hyposulphite solution is so energetic that it will bleach down the darkest of sepia prints if not previously put in water. Purple tones are obtained, after washing, by treating with any gold-toning bath. Charles R. King.
Staple Hill Park, Bristol, England.
It is occasionally necessary to bleach blue-prints when it is desired to make drawings for photographic reproduction. Blue-prints are sometimes so faded that it is impossible to trace them, in which case I Ink the lines of the blue-print and then bleach out the blue, leaving the black lines on the white ground. The process of bleaching is extremely simple and is one that I developed about eight years ago. I had found it impossible to make tracings from blue-prints which were very much faded, or which had been over- or under-printed. After experimenting for a month or so, trying different preparations, I finally hit on the following combination:
1 gallon lukewarm water and ½pound bicarbonate of soda. Of course this proportion is not exact, and has to be used with caution; when in doubt prepare a little solution and make a test of a small piece before hand as it will be found that some prints will not bleach as others do. Do not allow the inked-in prints to remain in the solution any longer than is absolutely necessary, for no matter how waterproof the ink may be it is impossible to keep it from running a little. Freshly made blue-prints, that is, those not more than a few months old, work best. As soon as the print is bleached take it out of the solution by the corners, being careful not to touch the ink work. Too much soda is harmful as it deposits white dust on the lines. This, however, can be removed by re-immersion in clean water.
New York. Fred Dibelius.
The following solution will change the color of blue-print paper to a dark brown: Borax, 2½ ounces; hot water, 38 ounces.
When cool, add sulphuric acid in small quantities until blue litmus paper turns slightly red, then add a few drops of ammonia until the alkaline reaction appears, and red litmus paper turns blue. Then add to the solution 154 grains of red crude gum catechu. Allow this to dissolve, with occasional stirring. The solution will keep indefinitely. After the print has been washed in the usual way, immerse it in the above bath for a period of a minute or so longer than necessary to obtain the desired tone. An olive brown or a dark brown is the result. John B. Sperry.
Blue-prints that have become burned or over-exposed, may be saved by the use of the following formula: Make a saturated solution of bichromate of potash, and keep a supply on hand in the blue-print room. If a print becomes over-exposed, wash it in the usual manner in a tank or tray of water, after which place it in another tray which should contain a mixture of two parts water to one part of the saturated solution of bichromate of potash. Allow the print to remain in the tray containing the solution until it shows a deep blue color and the white lines are clearly defined (which requires but a few seconds), after which the print should be thoroughly washed and rinsed in clear water. The proportion of the bichromate of potash may be increased or diminished as the occasion requires. This solution also acta equally as well when applied to white-prints made from vandyke negatives. Prints, as well as expense and time, may be saved by the use of the above solution.
Meadville, Pa. J. C. Hassett.