Two formulas have been given in these columns for blue prints. We add one more:
No. 1.
| Citrate of iron and ammonia | 1-7/8 | oz. |
| Water | 8 | " |
No. 2.
| Red prussiate of potash | 1-7/8 | oz. |
| Water | 8 | " |
The iron mixture may be made up, and will keep for a long time. The potash mixture will not keep over five or six days. Place the paper on a flat board and dampen it with a sponge. Turn equal parts of each mixture into a saucer, mix thoroughly, and apply to the paper with a flat brush. A letter-copying brush is the best kind of brush, as it is broad and soft. Put on just enough to cover the paper evenly without streaking it. As soon as the solution has set, hang the paper up to dry. It should dry quickly, for if it is a long time in drying it will be streaked.
Sir Knight MacM. Towner writes that a short time ago he made some blue-print paper from directions given in the Camera Club, and when finished the paper was yellow, with blue spots in it, and asks what is the reason. The trouble is in preparing the solution. Mix the two solutions thoroughly before using, and apply lightly and evenly. Sir Kenneth says he prepared the paper by lamp-light, though the directions did not tell whether to do so or not. Referring to the copy—No. 797—which contains the directions for blue prints, we find it reads, "The paper must be sensitized by gas or lamp light, and dried in a dark room." "To sensitize," means to apply the solution to the paper. If Sir Kenneth has any more trouble in preparing his paper, he is requested to send a sample to the Camera Club. The plain salted paper which Sir Kenneth asks where to buy can be obtained of any dealer in photographic goods, or if he does not have it in stock, he will order it. It should be freshly salted.
Natural History Morsel.
Have you ever noticed the caterpillar as it spins its tiny web from the branches of trees, descending as the web is completed to the ground and returning by its newly made ladder? If you have never noticed it, you would be well paid to watch caterpillars in their work. I have spent a great deal of time watching them, and find them an interesting study. I would like to have a few foreign correspondents, and have stamps to trade.