It is the habit of some to use a double-coated plate like the Standard Orthonon on practically all copies. That is wrong for the best results. While the Standard Orthonon plate is a little bit harder in contrast, for instance, than a portrait film, it is a little soft working in contrast for most copies. A Com mercial or Commercial Ortho film, Cramer's Medium Iso or Hammer's medium speed of plates will give better results but, of course, as above mentioned, if you use single-coated plates they should always be backed, whereas, with a film this is not necessary.
The lens to use should preferably be an anastigmat of good make, although a rectilinear will do very well when stopped down.
I suppose it is hardly necessary to mention here that the copy hoard, lens and ground-glass should all be exactly parallel.
There are several things that cause trouble in copying. I will take up a few of them and give a few points in that connection.
The first is sepia prints. A sepia print, copied in the ordinary way, is a disappointment. For really good results, use a panchromatic plate with a red contrast filter and, while that increases your time a lot, the results leave nothing to be desired.
With blue prints, which the commercial photographer is often requested by architects, engineers, etc., to photograph for reproduction, the best results are obtained by using a red contrast filter and a panchromatic plate. However,
fairly good results can be secured by using a yellow sensitive plate and the "G" yellow contrast filter.
Then, again, you will get pencil sketches on rough paper. They can best be handled under glass, using a process plate or film and a very light filter such as the Kl of the \Vratten series.
There is another job of copying occasionally coining up, and that is copying from a book, the paper stock of which is known as India paper, very thin, and where the printing on the opposite side of the page shows through. By putting a piece of black paper in back of it and photographing with a process plate or film, giving just the right exposure, you can lose the print on the other side.
Still another job often encountered is where it is necessary to patch originals for copies and, at the same time, return the original in good condition and without the patch. A little stunt comes in handy here, and that is, to use rubber cement—just the common tube variety used in mending auto or bicycle tires. Rub it lightly on the patch, as well as on the surface where the patch is to be placed, letting it dry down some, then put the patch in position and roll it down. When through copying lift off the patch and if some of the cement clings to the original, it can be cleaned off with gasoline or benzine.