US2122859A - Process for making plates for color printing - Google Patents

Description

PROCESS FOR MAKING PLATES FOR COLOR PRINTING Filed Jan. 9, 19-37 3 Sheets-Sheet l INVENTOR. E/ERETTIZPEA ro/v,

ATTORNEYS y y E. R. EATON 2,122,859

PROCESS FOR MAKING PLATES FOR COLOR PRINTING Filed Jan. 9, 1957' 3 Sheets-Sheet 2 fisksrrfaE/qrolv.

ATTORNEYS INVENTOR? g "Q July 5, 1938. E. R. EATON 2,122,859

PROCESS FOR MAKING PLATES FOR COLOR PRINTING Filed Jan. 9, 1957 3 Sheets-Sheet 3 INVENTOR. EVERETTE. 5470M ATTORNEYS Patented July 5, 1938 UNITED STATES PROCESS FOR MAKING PLATES FOR COLOR PRINTING Everett R. Eaton,

McCall Corporation,

poration of Delaware Darien, Conn., assignor to New York, N. Y., a cor- Application January 9, 1937, Serial No. 119,736

4 Claims.

My invention relates to the preparation by photoengraving of plates for printing in color and more particularly to processes for blocking out certain areas in making plates for half-tone printing. 7

In multicolor printing, successive impressions in different colors are superimposedj the colors generally being the three primary colors, and black. Shades such as green or purple are formed by the superposition of appropriate shades or tones of the respective primary colors of which they are constituted. Each impression is made by a separate plate having printing areas to print its respective color where the color is to appear in the final picture and with a depth of intensity to correspond with the color efiect desired. Areas of one plate may coincide with or overlap areas of another plate to produce an intermediate shade. For example, in producing an area of a green color or shade it will be printed with both blue and yellow. These various areas must be exactly positioned since if one, for example, the blue area, is slightly oiTset the resulting composite shade, of green, will have an unwanted margin of blue.

In making the printing plates by photoengraving, a negative of an original color sketch or picture is made for each plate by using a filtered light so that light is reflected from those areas of the sketch or picture in which the respective color appears either in a pure color or in a composite color. For example the negative for printing the blue color would be formed by light not only from areas of pure blue but from areas of green, violet, lavender and similar tints. Similarly the negative for the yellow plate would include areas of green and orange, and the negative for the red plate would include areas of orange and purple shades. The intensity of the color must be appropriately varied, not only for the pure shades but also for the composite color shades. For example a green or a blue green would have light or lighter shades of yellow, and a purple or reddish purple would have correspondingly lighter shades than that for the pure color areas. In half-tone printing, in which a screen is inserted between the sketch and the negative so that the light reflected 'irom the sketch passes only through the meshes of the screen and is then separated into separate pencils of light, the negative is formed of dots of varying size to correspend with the respective light intensities and the resulting printing plate surface has projections of corresponding areas.

In practice, however, the reproduction of the colors obtained by merely photoengraving in this manner is not exactly due to the inability of the filtered light to reflect the selected color faithfully and to exclude all others, or to other causes or to a combination of causes. Plates made by 5 merely photographing with the selected filtered light would produce pictures that would be off color in whole or in part for example being too 7 dark or having areas in which a color such as red or blue is too prominent or too weak. The plates 10 must, therefore, be etched selectively by hand to eliminate or block out certain areas and bring out or emphasize others. Heretofore this has been a difficult task requiring a high degree of skill and with a danger that areas of separate plates for composite shades or colors, such as green or orange, may not exactly coincide and thus may produce offsh'ade margins.

For example, if certain parts are to be blocked out on the etched plate, it is necessary to protect those parts that are to be retained and then to etch away the parts to be eliminated. It is, however, diflicult for the etcher to find and accurately paint in on a chalked up etched plate, particularly when the detail is smaller than the original sketch due to reduction in size. Also in certain tones as for example those bordering on pure white, it is frequency very hard to find the outlines of the areas and to hold such fine distinctions in tone particularly in light, or near white, shades.

In my present invention these difliculties are eliminated to a very large extent and a process is provided in which the elimination of a particular color is greatly facilitated and the correspondence in area of two superposed colors made substantially certain.

In my process, in making the negatives from a colored sketch, a transparent thin sheet of Celluloid is superposed on the original sketch or pic- 40 ture and provided with identification marks to ensure accurate realignment and then those areas in which the selected color to be printed appear are outlined as for example with India ink. The outlined areas are then covered with a black color, preferably on the reverse side so as to produce a perfect black, and then replaced on the original sketch. An exposure of the sketch with the superposed blocked out Celluloid sheet is then taken on the negative, the half-tone screen being removed or placed out of focus. Preferably a sheet of white paper isinserted between the Celluloid and the skitch to produce a perfectly black and white object. This gives a dead exposure to all of the areas except the blockedout areas.

- a similar manner. The processis then repeated picture I 2. These register marks upon all of the areas that are taking a negative exposure first in dead black and white with both Celluloid sheets and then through the half-tone screen with the Celluloid and paper removed. For each color there will, therefore, be a transparent or celluloid blockout sheet or a combination. of such sheets. As a result an area of composite color, for example, green, will .be blocked out on the Celluloid sheet for blue and this sheet will also be used for yellow so that a second blocking out of this area is not required but only those additional areas in which yellow is to appear without blue. If yellow is not to appear at any area where the blue has been blocked out, it can be covered on its appropriate Celluloid sheet by dead white paint, such as Chinese white. This will have the same effect as though it had not been blocked out. .By using combinations of Celluloid block-out sheets the necessity of blocking out an area twice is avoided and correspondingly danger of variation in the blocking out of an area for two different colors is eliminated and all areas for composite colors are identical.

The various features of the invention are illustrated by way of example in the accompanying drawings in which Fig. 1 is a view of an original sketch and a transparent sheet superimposed thereon with certain color areas outoutlined for blocking out. Fig. 2 is a view of the reverse side of the Celluloid plate showing the manner of blocking out. Fig. 3 is a view of the blocked out sheet the white sheet being inserted between the two. Fig. 4 is a view showing the manner of photographing the original sketch and Celluloid sheet assembly. Fig. 5 is a similar view showing the photographing through a half-tone screen of the sketch with the Celluloid sheet removed Fig. 6

is a sketch with a second transparent sheet superimposed on the first sheet for blocking out a second color, and Figs. 7 and 8 show further combinations of Celluloid sheets for additional colors.

Referring to .the accompanying drawings, register marks l0 and II are placed on a sketch or Ill and H are preferably in the form of a cross made with a fine ruling pen. 'Ihen a transparent sheet l3 such as a sheet of Celluloid of a thickness of .005 of an inch is superposed on the sketch l2 and suitably secured as with decorators Scotch tape. Register marks are placed on this sheet to correspond with the register marks l0 and H of the original, care being taken to have them in perfect alignment with the original. Thereto retain a tone for the particular color selected are outlined as at l4, l5, l6, l1 and I8. For example, if a blue plate is to be madethese areas would be those containing blue or some color containing blue, as for example green or violet. These areas are then filled in by a black coating. To obtain the blackest efiect in these areas the Celluloid sheet is removed and turned over and cellulose replaced on the original sketch,

opaque or similar covering material is filled in on the reverse side of the cellulose sheet covering the areas outlined.

For example, as shown in Fig. 2, the area Hi is being filled in or blocked out and the areas l4, l5, I1 and I8 will be similiarly opaqued. Then the Celluloid sheet or mask thus formed is placed in its original position on the sketch l2, the register marks I0 and l l of the mask being carefully positioned to coincide with those of the original sketch. The mask is firmly secured by Scotch tape. The areas of the sketch which are to contain the tones of the color whose plate is to be made are therefore now covered with black. To produce a black and white object, a sheet of white paper I9 is inserted between the Celluloid mask and the original sketch. As shown in Fig. 3, this covers up with white those areas of the sketch that are not blocked out.

Fig. 3 shows the process duringthe step of inserting the paper and its effect in changing the assembly to a pure black and White object. The sheet of paper will be either sufficiently short not to cover the register marks ill and II, or will have openings through which these marks can be seen. In the latter case the paper may be placed on the sketch and the mask then mounted on it. The assembly of mask and original is now ready for first exposure to the negative.

Although no special equipment is necessary, a glass front tilting copyboard is desirable for producing the best results. The operator or cameraman first places the original copy on the board fastening it into position so that there will be no danger of its moving later on. This may be fastened with adhesive tape or Scotch tape. Over the original 2. sheet of white paper may be placed, openings being provided through which the register marks can be seen. The Celluloid mask is then placed in position with its register marks coinciding exactly with those of the original. Over this assembly there is then placed a sheet of plate glass to hold the Celluloid mask in close contact with the original copy.

With the plates thus prepared, the operator makes an exposure on a sensitive plate with the half-tone screen either entirely removed or moved to such position that it does not form the light rays from the original into pencils but diffuses it. This is preferable to entirely removing the screen as it does not require any change in the focus of the camera. A sufiicient distance for the screen in this operation is approximately halt the distance between the normal distance of the screen from'the sensitive plate for half-tone work and the. greatest distance which the camera adjustment permits.

The positioning of the original I2, the screen I 9 and the camera 20 as. shown in Fig. 4 illustrates the arrangement for this exposure. The exposure is continued sufliciently long so that those parts in the original and mask assembly that appear white will cause a dense opaque black area in the negative. After this first exposure has been completed the lens is capped, the screen moved back to its proper position as shown in Fig. 5, the Celluloid mask and white sheet of paper removed from the original and a half-tone exposure is made on the negative in the usual manner; thereupon the negative is developed,

Celluloid mask' and dense and opaque without semblance of dot' formation in those areas which were not blocked in in the mask. A print on copper is then made from this negative in the usual manner after which the etcher spots up the plate,

paints in dead metal leaving the usual s" channel around the live portions, coats the back with an acid-resisting ink and flat etches the plate. Then the plate is deep etched and cleaned off and is ready for whatever staging and re-etching are required to balance the colors on the various plates. After this is completed the plate is ready to be trimmed, routed and proved in the usual manner.

In making the next color plate, for example, yellow, as indicated in Fig. 6, the mask I3 is placed on the original sketch l2 and fixed in place with the register marks exactly registering, then a second Celluloid sheet 2| is placed on the mask l3. There will be certain areas, for example, green, which must be blocked out for yellow as well as for blue, but having beenblocked out in the mask l3 do not need to be additionally blocked out on the mask to be formed on the sheet 2|. Certain additional areas, however,'may have yellow in a color combination and not blue, as for example in pure yellow or orange. Assuming, therefore, that the areas l6 and II are green and that the adjacent borders 22 and 23 are orange these would now be blocked out in a manner similar to the areas l6 and I1. The stocking areas 24 and the flesh colored areas, such as the hands and face 26, might also be blocked out for the yellows. If there are any parts that have been blocked out for blue and which are not to contain any yellow, these areas may be covered with'Chinese white on the mask 2| which will have the effect of eliminating the blocking on the mask I3. When this has been completed and opaqued the two masks are placed on the original, the white sheet 19 again inserted and the two exposures made; thereupon the printing plate may be made as described above,

To make a plate for the red, the masks l3 and 2lmay be replaced, care being taken to register both of them on the register lines and a third transparent Celluloid sheet 21 superposed on them. All areas containing blue and yellow are already blocked out by the masks l3 and 2|, and it is only necessary to block out those additional areas which are to contain the red color. As the areas 22, 23 and 24 have been blocked out for the yellows, as have also the areas 25 and 25 which may contain some red, it is only necessary to block out the additional areas that contain red but not yellow or blue. Such, for example, might be cuff areas 28. A negative is thereupon made by double exposure and a plate made in the manner described above.

In making the fourth or black plate, still another sheet 29 is placed on 7 and those additional parts of the sketch which are to be printed in black are blocked out. If any areas are to appear in pure white, they may remain unblocked as, for example, the neck band area 30 and the handkerchief 3|. A negative is again made by double exposure of the assembly and the original sketch and a plate made as described above. Areas which appear in black are blocked out as shown at 3| and 32.

In the event that the sketch contains no combination of blue and red so that there are no areas blocked out for these two colors, but does contain combinations of blue and yellow and red and yellow, the mask l3 might be omitted colors.

the assembly of Fig.

from the red mask, that is, it would be omitted from the assembly shown in Fig. '7.

In some cases it may bemore convenient to combine certain masks to produce each of the For example, each color mask may be made up of one or more masks. This enables a greater flexibility to be obtained without the necessity of blocking out certain areas with Chinese white or white pigment. For example, a series of three masks might be used in which the red would be made of masks I and II, the black of'masks I and II, the yellow of masks I, II and III, and the blue of masks II and III.

In this case it will be apparent that the mask I covers combinations of yellow and red and incidentally black; mask II covers any combinations of red, yellow and blue as well as black; mask III covers combinations of yellow and blue. In any event those areas that contain more than one color tone require blocking in only once. This not only has the advantage of eliminating the labor of blocking, which may be considerable for a complicated design such as a flowered or other fine design, but it ensures perfect alignment of these two areas. As the areas are made in outline directly on the. original, it is relatively easy to trace these outlines even through they are between relatively light shades and pure white. Vignetted outlines may, therefore, be traced with perfect accuracy.

This avoids the necessity .for the etcher to pick out on a plate, which may be reduced in size, an exact spot corresponding for example to yellow on the original sketch. Because the colors have been separated, that is the reds from the greens, the yellows from the purples, etc., it is advantageous to get a proof of the work directly after the plates have been fiat etched and deep etched. With this proof as a guide the etcher can the more easily and more quickly balance the colors to match the original.

What I claim is:

1. A process of photographically forming a negative for a halftone printing plate for multicolor printing, from a colored original which comprises forming a number of masks each comprising a transparent sheet having at least one black opaque area, the black opaque area of each mask being different in outline and position from the black opaque area of the other said masks to block out all areas of the original of a selected hue, exposing a light sensitive element in a camera first to said original through a combination of more than one of said masks superimposed in register to block out the combined opaqued areas of the combination of masks covering all areas of the original containing the color value of the plate to be made and then exposing said light sensitive element to said original without said masks normal position to of a selected color through a halftone screen in obtain a halftone negative value.

2. A process of photographically forming a printing plate for multicolor printing from a colored original which comprises forming a number of masks each comprising a transparent sheet having at least one black opaque area, the black opaque area of each mask being different in outline and position from the black opaque area of the other said masks toblock out all areas of the original of a selected hue, exposing a light sensitive element in a camera first to said original through a combination of more than one of said masks superimposed in register to block out the combined opaqued areas of the combination of masks covering all areas of the original containing the color value of the plate to be made and then exposing said light sensitive element to said original through a halftone screen in normal position without said masks to obtain a halftone negative of a selected color value, developing and fixing the resulting negative and photoengraving a print therefrom.

3. The process of claim 2, in which a proof is taken of said printing plate and said printing plate is then re-etched to modify the color tones. 4. The process of claim 1, in which a white opaque sheet is inserted in the assembly of masks and original between the original and its superposed masks during the first exposure thereof.

EVERE'I'I R. EATON.

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