US2494765A - Chemical erasing of photographic silver images - Google Patents

Description

Patented Jan. I 7, 1950 CHEMICAL ERASING OF PHOTOGRAPHIC SILVER IMAGES John F. Kienast, River Edge, N; J assignor to Keufiel & Esser Com corporation of New J c pany, Hoboken, N. J,, a rsey No Drawing. Application November 10, 1944, 'fSerial No. 562,916

This invention relates to a method for and compositions useful in the making of erasures on photographic prints.

In engineering reproduction materials and particularly those which employ silver to produce the visible image, it is oftentimes desirable to make erasures by removing the silver which colors some of the areas, either to correct errors or to remove lines from certain portions in order that they may be corrected or redrawn.

The invention is applicable to many types of photographic materials on various base stocks such as paper, cloth, film, sheet metal, etc., including: those commonly referred to as vandykes, brown prints and the like where the image is created from a combined soluble silver salt and an iron salt; engineering reproduction materials with silver halide emulsions; engineering reproduction materials having gum or glue bichromate with silver images and the like; and may also be used for correcting ordinary photographic film as well asphotographic prints which latter are oftentimes referred to as photoprints or photocopies.

In the past, various procedures have been proposed for making the corrections in a silver image and one of the early methods included the application of a single fluid eradicator, the principal constituent of which was mercuric chloride. Erasures made with this material were fugitive and became opaque when exposed to light, corroded pens and drawing instruments which were later used on the areas, had some danger from toxicity and produced "ghosts which showed up when the photographic material was used for reproduction purposes.

Some improvement in erasing fluids occurred by applying hypochlorite in the form of sodium hypochlorite which was the first step in removing the image. For the second step the area was treated with a hypo fixing solution. Results were not generally satisfactory or uniform because it was difficult to stabilize the hypochlorlte which deteriorated in storage or, if stabilized with alkali, had a deleterious effect on the base material when applied to make an erasure. It was diflicult to make a drawing over an erased area particularly when ink lines were employed, as

the ink spread through the base which was oftenso weakened that it would crack or disintegrate.

It has now been discovered that the undesirableeffects and disadvantages of prior art methods can be avoided by using two solutions successively in the manner hereinafter described, when it i '1 Claims. (01. 95-43) desired to make erasures of images which were created'photographically from silver salts.

In order to carry out this invention; a eupric halide, preferably cupric chloride, is dissolved in water in quantities ranging from 3% to with best results obtained from cupric chloride representing approximately 15%. This material is stable in storage, the desired concentration is readily secured and it does not in any manner attack the base sheet.

Improved results are obtained by the addition of an ammonium halide which may correspond with the cupric salt. Where thisis ammonium chloride, it is used in amounts ranging from a concentration of 5% to as high as 25% with amounts approximately 15% being satisfactory for most purposes. The solubility of the ammonium chloride is determined by theamount of the cupric chloride already in solution, that is, the greater the concentration of cupric chloride theless ammonium chloride will go into solution. It is preferable to use the maximum quantity that can be dissolvedin the cupric chloride solution already prepared. The ammonium chloride improves the action of the first fluid by increasing the speed of makes possible a fluid is applied, which is somewhat cleaner, i. e. more complete, than if the cupric chloride is used alone in the first solution.

A preferred solution portions-z Distilled water, 1000 cc. Cupric chloride (CuClz.2HzO), 167 gms.

The second solution used for making erasures is an aqueous solution of thiourea. Preferably,

this solution also contains a suitable wetting agent of the types herein set forth. In the preferred composition the thiourea is dissolved in water to make a saturated solution. About one and one-quarter (1% lbs.) poundswill dissolvein one gallon of water at normal room tempera-1 Such a solution with small amounts of a wetting agentis stable under conditions of.

tures.

normal storage and use. To either theerasing fluid or the fixing fluid or both, a wetting agent such as alcohol, sulphonated alcohol, di hexyl sodium sulfosuccinate.

or the like may be added in small amounts. l In order to make an erasure, the cupric chloride solution, with or without ammonium chloride and.

a wettingagent. is applied to the area where the the first reaction and it also final erasure after the second' has the following pro-.-

blotted from: the surface promptly after ithas been applied uniformly over the area to be treated. After the excess liquid has been removed by blotting, the second solution of thiourea and the wetting agent is applied to the same area though for many types of engineering reproductionsit need not be so limited. The solution may be permitted to dry on the sheet but: it is usually; preferred to remove blotting. It can, of course, be

avoided.

The combination of the cupric chloride solution and the thiourea solution for erasing has many advantages over other erasing fluids. A prior two-fluid combination for erasing which included a first solution comprising cupric chloride presented diifi'culties in use because it was necessary to insure thorough conversion of the image withthe cupric chloridebefore its blotting and the application of a fixing solution, otherwise the erasure will not be complete and even if the process is carried out carefully it is possible that there may be some staining of the print, a condition which is particularly undesirable where engineering reproductions are concerned. This was likely to occur in those cases where the print had been prepared-under conditions where special treatments had been given either" to accelerate the original reproduction process or where final washingwas inadequate or incomplete. Under such cases residual salts left in the base material adversely affected theerasing action and in some instances resulted in producing'colored compounds that left an apparently permanent stain in the drawing.

Where the present composition is used, i. e. the thiourea solution is applied to the print'aft'ei' treatment with the cupric chloride solution, the critical procedural details formerly necessary can be dispensed with. Excellent erasures are secured evenwhere residual salts from the original" development have not been adequately or completely removed. The erasure restores the original color of the base sheet.

Instead of using cupric chloride for the first solution, other oxidizing or decolorizing solutions may be employed. Another. is ammonium or potassium persulfate saturated solution which, however, has no discernable efiect when first applied but produces the erasure when the solution of thiourea is also present; These two solutions cannot be premixed though both must'be present simultaneously.

The compositions herein described, when used in the process as set forth, will remove silver images from paper, cloth, film, metal or other bases normally used as supports for light sensitive layers containing silver and will produce erasures which are very permanent and do not affect the base either as to strength or" as to ability to receive redrawn lines. The erasure does" not leave any residue which appears on the'print when the. erased sheet is used in making reproductions as, for example, by contact printing.

The cupric chloriderequired in the firstfluid may be obtained not'only by dissolving the'salt' cupric chloride in waterbut also by providing the residual liquid as by washed from the surface in any known manner but this results. in unduly Wetting the sheet and is preferably 1 Cupric fluoride works slowly upon and from 25' to in solution the divalent cupric ion from any other source such as copper sulfate and the chloride ion from any suitable chloride salt as, for example, sodium chloride thereby providing in the solution the divalent cupric ion and the chloride ion. :The ammonium chloride desired inthe solution may also be provided by theionization of ammonium salts and chloride salts.

Other cupric halides in addition to the cupric chloride discussed above may be used although results are generally not as efiective. For example, cupric bromide works very slowly and the addition. of ammonium bromide has no noticeable effect. Onthe other hand, the addition of ammonium'chloride greatly improves the action. the addition of. ammonium fluoride and, of course, more rapidly if ammonium chloride is added.

It should be understood that where reference is made to a solution of cupric halide, this expression is intended to'mean that the solution contains cuprlc'ions and halide ions even though not obtained directly by the solution" of the cupric halide;

While the invention. has been described with reference to certain preferred procedures and compositions, theseareto be considered as illustrative of the invention as defined in the appended claims.

Iclaim:'

l. The process for erasing silver images on bases which comprises applying to that portion of the image'which is to be erased a solution containing between 3 and 58% of cupric chloride 5%. of ammonium chloride, treating the areato which the cupric chloride solution was applied-with a substantially saturated solution of thiourea-and removing the resulting solution.

2. The process for erasing silver. images on baseswhich comprises'applying to that portion ofv the image which is. to be erased a solution containing cupric chloride and 15% ammo-- nium chloride, treating the area to which-the cupric chloride solution was applied-with a substantially saturatedsolution of-thiourea and removing the resultingsolutionn 3. Aucompositionior making erasures oi silver images which comprises anaqueous solution consisting essentially of- 3 to 50% cupric chlo-. ride andammonium chloride ina sufficient concentration of iron 1.25 to 5% to form a substantially saturated solution in water.

i. A composition for making erasures of'sil-.. ver images which comprises an aqueous solu,

tion consisting essentially of a, wetting agent,

from 3 to 58% cupric chloride and ammonium chloride in'a suiiicient concentration of from to 5% to form a substantially saturated solution in water. I g 7 5. A composition for making erasures of silver images by applyingthecomposition to-that portion of theimage which is to beerased and thereafter treatingthe area' towhi'ch the com position has been applied with a substantially saturated solution of 'thicurea, said eomp'os ionconsisting essentially of 1 approximately 15% cupric chloride ammonium chloride in a suilicient concentration of approximately15%"to 2 form a substantiallysaturated solution in water 6. The process for erasing silver images on bases which comprises applyingto-that portion of the-image which is to be erased asolution" containing'betweens and ofcupric chleride, treating the area "to which the cupric. chlo- REFERENCES CITED The following references are of record in the file of this patent:

Number Name Date 1,780,025 Mankenberg Oct. 28, 1930 1,945,658 Roessler Feb. 6, 1934 5 1,963,197 Frohlich June 19, 1934 2,000,353 Schaeffer May 7, 1935 2,100,594 Heymer Nov. 30, 1937 2,107,094 Townsend Feb. 1, 1938 2,166,617 Weber et a1. July 18, 1939 10 2,311,015 Young et a1 Feb. 16, 1943 2,322,084 Young et al June 15, 1943 2,327,822 Russell et a1 Aug. 24, 1943 OTHER REFERENCES 15 Clerc: Photography Theory and Practice,

6 U'NI'I'ED STATES PATENTS Pitman 8: Sons, New York, 1937, p. 270 cited.

Claims (1)

1. THE PROCESS OF ERASING SILVER IMAGES ON BASES WHICH COMPRISES APPLYING TO THAT PORTION OF THE IMAGE WHICH IS TO BE ERASED A SOLUTION CONTAINING BETWEEN 3 AND 50% OF CUPRIC CHLORIDE AND FROM 25 TO 5% OF AMMONIUM CHLORIDE, TREATING THE AREA TO WHICH THE CUPRIC CHLORIDE SOLUTION WAS APPLIED WITH A SUBSTANTIALLY SATURATED SOLUTION OF THIROUREA AND REMOVING THE RESULTING SOLUTION.