US2388107A - Production of photomechanical printing surfaces - Google Patents

Description

1945- E. ZIEGER 2,388,107

PRODUCTION OF PHOTO-MECHANICAL PRINTING SURFACES Filed June 22, 1945 Patented Oct. 3.0, 1945 v OFFICE zsaaior OF PHOTQMECHANICAL G SURFACES mm z ieger, West Didsbm'y, Manchester, England Application June 22, 1943, Serial No. 491,814 In Great Britain June 25, 1942 4 Claims. (c1. sis-5.1)

This invention is concerned with the prepara tion of patterns or designs by photographic methods for use in the production of printing surfaces.

and has for its object to simplify the process by which variations in the coarseness or fineness of screen markings are produced upon the photographic negative to represent the gradations of depth of colour in the pattern to be printed.

The invention consists in a process of making a single photographic negative of the parts of a design of different shades of the same colour, which comprises exposing the negative as many times as there are shades of the same colour and each time to light passing through a different grade of shading medium, each exposure dealing only with areas of the negative corresponding with the parts of the design of one shade of the same colour.

The invention further consists in a process of making a single photographic negative of the parts of a design of different shades of the same colour, which comprises exposing the negative as many times as there are shades of the same colour to light from artists sketches, each of which includes as opaque areas only parts of the design of one shade of the colour, the light at each exposure passing through a different grade of shading medium, each exposure dealing only with areas of the negative corresponding with the parts of the design of one shade of the same colour.

Referring to the accompanying explanatory diagrams which are designed to illustrate in the simplest possible manner how the present invention is carried into effect in one particular form:

Figure 1 shows what is termed the design which it is desired to reproduce and from which a printing roller or surface for each separate colour has to be made.

Figure 2 shows the mask which is prepared to blank out the design of Figure 1, those parts thereof of which are in a single colour.

Figure 3 illustrates the effect of the first exposure of the photographic film or plate using 'the mask of Figure 2.

Figure 4 shows a second mask designed to blank out from the part of the design of Figure 1 which is in a single colour, that part which is in one shade of said colour, there being in the design shown, two shades of one colour.

Figure 5 illustrates the effect of the second ex-' posure of-the photographic film or plate using the mask of Figure 4 with a suitable screen for thenew part of the film exposed to'light in the second exposure compared with what was exposedto light in the first exposure.

' Figure 6 illustrates the effect of the third exposure of the photographic film or plate where themask of Figure 4 is employed but where light reflected from the opaque part of the mask is transmitted to the film or plate through a screen of a different degree of fineness from that employed in producing the Figure 5 result.

In Figure 1, the design comprises two parts a and b in different shades of one colour, and a part c of a different colour. It will be :appreciated that an actual design may be very complicated and contain several colours situated in many parts of the design and many shadesof each colour. Whatever be the nature of the design, a photographic representation or negative has to be prepared of each colour, with screen markings of varying degrees of fineness or density to represent various shades of the one colour.

An artists sketch or mask A as indicated in Figure 2 is now made on a transparent base which represents by the opaque area d, the parts of the design (i. e.'a and b) to be reproduced, which are in one colour though they are of different shades of that colour, that is to say both full and half shades. This mask A is now photographed with light transmitted therethrough'upon a film or plate exposed in a camera, so that the said opaque part (1 of the mask A is represented on the film or plate by a sensitive or unexposed part c, whilst the remainder of the film or plate is exposed. A second mask B is now made as shown in Figure 4 to cover the part b of the design which is to be of say half shade or depth of colour in the reproduction. The photographic film or plate is now exposed again in the camera to photograph the mask B (Figure 4) but this time the light transmitted to the sensitive parts of the film or plate is passed through a coarse screen or shading medium of any desired character, such as a line, stippled, half tone or cross hatched screen. This results in the part i of the photographic film or plate (Figure 5) being shaded. A further exposure of the film or plate is now made to light reflected from the opaque portion 9 of the mask B shown in Figure 4 and transmitted through a suitable screen or shading medium. This results in the last portion'h of the film or plate.

It will be seen therefore that the negative developed from the film or plate contains representations of all parts of the design to be reproduced in one colour with different screen markings to give in the reproduction (after the printing surface such as a copper roller has been made in the The screens may be placed in the camera or over or under the artists sketches.

Where light has to be passed to the photographic film or plate from a transparent part of a mask, this light can be passed through such transparent part or reflected therefrom when suitably backed.

With my improvement I simplify the process 01' producing the negative for use in making the copper roller or other printing surface as only one negative is used for the one colour, the colour shades being obtained by repeated exposures using masks and screens. The word masks used in this specification indicates artists sketches traced from the original design, the first sketch differentiating between the parts of the design which are of the same colour and the other parts of any other colour, and each of the remainder of the sketches showing parts of the same shade of the selected colour. These masks are photographed and not theoriginal design.

What I claim is:

1. In the production of photomechanical printing surfaces, the process of making a single photographic negative of the parts of a design of different shades of the same colour, which comprises exposing the negative as many times as there are shades of the same colour and each time to light passing through a different grade of shading medium, each exposure dealing only with areas of the negative corresponding with the parts of the design of one shade of the same colour, the other areas being blocked out by masking during such exposure.

2. In the production of photomechanical printing surfaces, the process 01' making a single prises exposing the negative as many times as there are shades of the same colour to light from artists sketches, each of which includes as opaque areas only parts of the design of one shade of the colour, the light at each exposure passing through a different grade of shading medium, each exposure dealing only with areas of the negative corresponding with the parts of the design 01 one shade of the same colour, the other areas being blocked out by masking during such exposure.

3. In the production or photomechanical printing surfaces, the process of making a single photographic negative of the parts of a design of two shades of the same colour, which comprises exposing the negative twice to light from an artists sketch which includes as opaque areas only parts of the design 01' one shade, one exposure through one shading medium being to light from the transparent parts of the artists sketchand the other exposure through a different grade of shading medium being to light from the opaque parts or the artists sketch, each exposure dealing only with areas of the negative corresponding with the parts of the design of one shade of the same colour, the other areas being blocked out by masking during such exposure.

4. The preparation of a photographic negative of a design for use in the production of printing surfaces by a process which comprises 1) the preparation of a mask which blanks out the parts of the design which are in the same colour though of difierent shades of that colour, the remainder of the mask being transparent; (2) the exposure in a photographic camera of a, sensitive film to light from the transparent parts of the mask, and

(3) the subsequent exposure of the sensitive film,

as many times as there are shades of the same colour, and each time to light passing through a different grade of shading medium, each exposure dealing only with areas of the sensitive film corresponding with the parts of the design of one shade of the same colour, the other areas being blocked out by masking during such exposure.

EUGENE ZIEGER.

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