BLUE PRINTS, VANDYKES AND PHOTOSTATS Many photographers, who are connected with industrial plants, engi neering and architect's offices, have charge of the blue printing department ; also many commercial photographers make large num bers of blue prints from dry plate negatives, while the larger commercial studios doing merchandise set-ups and catalogue work for out-of-town customers use the blue print for customers' proofs.
There are several reasons why this latter is done. Should the proof fall among unscrupulous people, it cannot be used for reproduction purposes, as the blue print will not reproduce by the half-tone process to any degree of satisfaction. Another reason is that the blue print is cheaper, and, with many customers, such as furniture manufacturers, manufacturers of stoves, statuary, picture frames, etc., where the goods are known, but only new designs want to be shown, blue prints fill the wants very nicely.
'While the average commercial photographer looks upon blue prints as a nuisance, they are really the source of a great deal of profit when handled right and in quantities.
Blue print paper, as purchased in the open market, comes in three degrees of speed—slow, medium and fast—also conies in several grades of quality as to paper stock that it is coated on. If you are making blue prints from drafting room tracings on a continuous blue printing machine, you will need either the fast or medium speed. If making blue prints in a printing frame out in the sun, a slow or medium speed is -far preferable. The medium speed paper is also used in printing from dry plate negatives.
Illustration No. 78 is a continuous printer, washer and dryer and is one of several different kinds on the market, and this machine has the paper fed to it in continuous rolls and is printed, washed and dried and rolled up on the other end. It makes a very good outfit for studios doing production work.
Blue print paper, at its best, does not keep very long, deteriorating very rapidly in a damp or light place. It should always be kept in a dark and dry place. For those who prefer to coat their own paper the following is a formula that gives very nice results: Water 4 gal.
Red prussiate of potash 9 oz. Citrate of iron and ammonia (green scales) 20 oz.
Iron and ammonium oxalate 54 oz.
Mix well in a barrel or crock and let stand for two or three days, and it is ready for use.
There are several different ways of printing blue print paper. You can print it in the sun, with arc lamps, or with Cooper Hewitt tubes. They are all satisfactory as far as I know, although the arc lamps are probably the speediest for all around work. The Cooper Hewitt tube people make an unusually large tube especially adapted for blue printing.
Professional blue printers always treat their prints with a solution of bichromate of potash to give a better blue—it also makes it more permanent. The method of applying this solution is about as follows: Enough solution of bichromate of potash is added to the washing water to make it a fairly deep yellow color and the prints are immersed in this. It has rather a bleaching action, so, therefore, many printers do what they term "burn 'em up"—that is, print them several degrees stronger than ordinarily before immersing in the bichromate. Other printers, especially those printing from dry plate negatives, dip their over-exposed prints directly from the printing frame into a strong solution of bichromate of potash, and then wash the print thoroughly. Either way gives satisfactory results. Illustration No. 79 is a coating machine for those who coat their own paper.