US1867576A - Process of reproducing natural wood finishes on metal and other surfaces - Google Patents

Description

Patented July 19, 1932 UNITED STATES.

PATENT; OFFICE EMIL LOETSCHER, OF D U B UQUE, IOWA PROCESS or REPRODUCING NATURAL woon FINISHES N METAL AND OTHER suaraons a No Drawing. Application filed April 28,

This invention relates to improvements in processes'for reproducing natural wood finishes on surfaces of materials such as metal or other wood substitute, and more particularly to improvements in the photogravure process of ornamentation by reproduction of natural wood finishes, which heretofore has included as the initial step that of photographing by means of a camera, the surface marking of a selected piece or panel of natural wood, and preparing the printing plates from the photographic negative.

The present process eliminates entirely the use of a camera as the medium for producing a photographic negative of a wood surface, but uses a thin sheet or veneer of the actual wood as the negative, and by taking a direct contact print onto sensitized paper to thereby produce a positive from which the printing plate is prepared.

' Although this so-called photographic method of wood grain reproduction on metallic or other finished surfaces has been extensively employed,it is not altogether satisfactory, the chief objection being the fact that it is impossible to reproduce the natural efiect of the graining, since it is necessary to enlarge the grain and texture of the original subject and to otherwise treat its surface in order to bring out the desired efiect and detail.

It is readily apparent that a wood surface, no matter how beautifully grained, is not a perfect photographic subject, for the reason that there is not a pronounced contrast between the background or foundation color and the graining, which is usually but a shade or so darker than the body of the wood. It is generally true, also, that the more beautiful surface efiects are those in which the contrast is least pronounced. Consequently, in reproducing a natural wood surface,by photographing it by means of a camera, a considerable portion of the surface detail is lost in the transmission from 1930. Serial No. 448,160.

subject to plate due to absorption and loss of the reflected light from the subject in passing through the lenses of the camera. Consequently, it becomes necessary to stain the wood and to enlarge the texture of the graining in order to bring out the desired contrast, and this, of course, results in an unnatural reproduction and one which tends toward a coarse and unfinished effect.

natural and perfect reproduction of grained wood, however, can be successfully and economically obtained by the improved process, which eliminates the use of a camera entirely, as a means of obtaining a positive print of the subject, but rather utilizes a very thin and therefore translucent sheet or veneer of the actual wood to be reproduced as a negative, and by taking a direct contact print onto a sheet of sensitized paper, this, when developed, becomes the positive 6 from which the printing plates are prepared. The details of the process will be understood from the following:

The particular wood which is to be reproduced isobtained in the form of one or several thin sheets of veneer of the desired area, and which is readily obtainable in commercial "thicknesses of from 1/80 to 1/ 100 of an inch.

This thin sheet of veneer is then applied in direct contact with a sheet of sensitized paper of any suitable commercial grade. and finish and then exposed to sunlight or artificial 'light until the desired degree of exposure is obtained. The sheet is-then developed by the usual process and becomes the positive from which the halftone or rotogravure plates are made, depending on the'process to be followed. In short, the present improvement contemplates only the production of the positive by a direct contact print, using a thin veneer as a negative instead of the customary method of photographing the surface of a piece of natural wood and developing the negative.

The veneer being very thin is translucent and, therefore, it is possible to print directly through the material reproducing every minute detail of pore and fibre in'its natural size and without exaggeration or resorting to other treatment in order to reproduce wit some degree of accuracy the original subject. Some care has to be exercised in carrying out the printing in order to obtain the proper exposure, but this can be readily acquired with a little practice and experience. It is particularly essential that close contact be maintained between the veneer sheet and the printing paper, so that the print will not be blurred where there is' a slight separation of the two. This is readily accomplished, however, by using a so-called vacuum printing frame well known in the photographic art, which makes it possible to hold the sheets in close contact during the printing operation.

After the direct contact print has been made, it is developed and dried, and becomes the positive from which a halftone plate or rotogravure cylinder is prepared in accordan'ce with the standard practice. Thus having prepared the positive by the method of direct contact printing, the process followed from that point on depends on the nature of the work to be accomplished. For instance, if a panel of some compositematerial is to be finished in imitation of a natural wood finish, the rotogravure process would preferably be used, the impressions being made on sheets of paper colored to give the proper foundation or base color of the wood. The sheets would then be treated with bakelite or other resinous varnish to give a hard and wear-resisting surface to the panel when the sheets are applied. Reproductions on paper for use as book covers may be made from halftone plates, and impressions of natural wood finishes may be applied to metal surfaces by the so-called offset process, using rolls for transferring the pigment from the plates to the metal, as in the present practice.

Although no claim is made to any of the steps in the process of reproducing natural wood finishes on surfaces other than the making of the positive by a direct contact print from thin sheets of veneer, there are nevertheless distinct advantages in using the direct contact method aside from obtaining accurate and natural reproductions of the subject in the positive. 7

Take for instance the rotogravure method of printing in which the positive print of the original subject is photographed through a rotogravure screen and then transferred to the rotogravure cylinder by a photo-engraving process. Where the nature of the work requires that the grain extend continuously around the cylinder, it is quite difficult to transfer the impression onto the cylinder by the usual photographic method so that the ain will match at the meeting edges of the impression, and hence it is necessary to resort to considerable doctoring in order that the irregularity will not be visible when the impressions are made. direct contact print method, however, this is avoided because the veneer sheets are so thin that numerous sheets may be taken from the same log or block of wood, and each sheet will have practically the same arrangement of graining as the adjacent-sheet. It follows, therefore, that two successive sheets of veneer when laid end to end, but with one reversed or turned over with respect to the other, the graining at their abutting ends will match without showing an appreciable break or joint. Thus, if a contact print is made of a size to correspond to the area of the rotogravure cylinder, the impression eventually transferred to its surface will show no appreciable break orjoint in the graining, so that the cylinder will print a continuous over- VVith the so-called all design without a visible mark or irregu- 1. In a process for re roducing natural wood finishes on surfaces, t e steps of producing a positive print by direct contact print of a sheet of natural wood veneer of such thinness as to transmit light therethrough, and making a printing plate from said print.

2. In the photogravure process of reproducing natural wood finishes on surfaces, the initial step of preparing a positive from a direct contact print of a thin sheet of the natural wood to be reproduced upon a sheet of sensitized paper, said sheet of wood bein of such thinness as to transmit light there'- through. I

3. In a process of reproducing natural wood finishes on base materials, the steps of preparing a translucent sheet of thin veneer of the wood to be reproduced, making a direct contact print of said veneer on a sheet of sensitized'printing paper, and transferring the subject of said print onto a metal printing plate by a photo engraving process. 4. In a photogravure process for reproducing natural wood finishes on base materials, the steps of preparing successive layers of veneer of the wood to be reproduced, said layers being in the form of thin translucent sheets, arranging said layers of'veneer and producing a printing plate from said print. n

5. In the rotogravure process of reproducing natural wood finishes on base materials, the steps consisting of preparing a plurality of thin translucent sheets of veneer from a block of the wood to be reproduced, arranging said sheets edge to edge so that graining matches at the edges, exposing said veneer sheets to light in direct contact with a sheet of sensitized printing paper, and transferring the resulting print to a rotogravure cylinder for continuous printing.

Signed at Dubuque, 1a., this 25 day of April, 1930.

EMIL 0. LOETSCHER.