From 50 to 100 copies may be made from one master copy. A turn of the handle brings a new gelatine surface.

3. The machine on the right is a jjortable that can easily be carried around if necessary.

It will copy a sheet as large as 8',i by 14 inches.

430«

flRAIHIg IRII

ENTATION

A. Arc Lamp.

Today it is possible to secure a continuous blue printing, washing, developing, and drying machine with either electrically heated or gas dryer.

The C. F. Prasr Company. Chicago. Illinois, and NfW York City.

Charle* Bruning Co , Inc , New York City.

B. Developing Machine for Making a Whife Print.

1. After the print, whether black and white, blue line, or a blue print, has been exposed

in a blue print machine, the print must be developed in a developing machine. The machine shown above develops a positive black and white print.

2. The Ozalid Corporation, New York City, makes a machine which exposes and drydevelops a positive print from a positive original.

METHOD

fWf

EPRODUC

'431

The principle of the blue print, white print, and blue line print machine is that chemically treated paper is first exposed to a chemical light action, which prints the design. The print is then developed, that is. treated so that the design will appear clear and remain semi-permanently. The first method of exposure was by means of blue print frames placed in the sunlight. The next step in the development of the present machines was the use of a single arc lamp. Later a bank of arc lamps placed side by side was employed. Since the convenience of operation seemed to fit into the reproduction field, mercury vapor tubes were utilized. It was later found that such tubes did not compare with arc lamps in the efficiency of printing.