US3839066A

US3839066A - High polymers for forming an invisible, soil-resistant coating on canvas

Info

Publication number: US3839066A
Application number: US00344791A
Authority: US
Inventors: A Brenner
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-03-26
Filing date: 1973-03-26
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01

Abstract

Protection against soiling of textiles and of paintings produced on unsized canvas with a paint consisting of a pigment suspended in an organic solution of an acrylic resin is achieved by application thereto of a viscous solution of a water-soluble resin which forms a semi-impervious, transparent, flexible plastic coating on the surface which is invisible to the eye and which is easily removed from the canvas without affecting either the canvas or any painting or other decoration thereon.

Description

United States Patent Brenner 1 1 Get. 1, 1974 [5 HIGH POLYMERS FOR FORMING AN 2,986,471 5/1961 Rudd 117/6 x INVHSHBLE SOILSESTANT CQA'HNG ()N 3,068,120 12/1962 Jacobson et al. l 17/ 139.5 C

CANVAS Inventor: Abner Brenner, 7204 Pomander Ln., Chevy Chase, Md. 20015 Filed: Mar. 26, 1973 Appl. No.: 344,791

References Cited UNITED STATES PATENTS 7/1934 Serrington 117/166 4/1936 Morrison 35/66 9/1943 Whitehead ll7/l66 X Primary ExaminerWilliam D. Martin- Assistant Examiner-Theodore G. Davis Attorney, Agent, or Firm-Lawrence I. Field ABST CT Protection against soiling of textiles and of paintings produced on unsized canvas with a paint consisting of a pigment suspended in an organic solution of an acrylic resin is achieved by application thereto of a viscous solution of a water-soluble resin which forms a semi-impervious, transparent, flexible plastic coating on the surface which is invisible to the eye and which is easily removed from the canvas without affecting either the canvas or any painting or other decoration f thereon.

l2 Claiins, N0 Drawings HIGH POLYMERS FOR FORMING AN ENVESEBLE, SOIL-RESISTANT COATING ON CANVAS This invention relates to the protection of paintings and textiles from soiling. More particularly it relates to the provisions of a relatively impervious, transparent flexible plastic coatings on canvas, which are invisible to the eye and which are easily removed from the canvas without affecting either the canvas or any painting or other decoration thereon.

Numerous incidents have been reported in the press of persons defacing paintings hanging in public galleries or in museums, wherein markings were made on the surface of the paintings, usually with crayons, aerosol sprays or other marking tools. The removal of such markings without damage to the art work is often difficult and time consuming.

Hence it will be evident that a need exists for a semiimpervious, invisible, flexible coating to protect artists paintings from soiling or defacement. The present invention is directed to the protection of a specific type of artists painting, namely paintings produced on urisized canvas with a paint consisting of a pigment suspended in an organic solution of an acrylic resin.

Paintings of this type were first produced about three decades ago. Because the canvas wasunsized, the paint soaked into it. The texture of the canvas was retained and the cloth had the appearance of having been dyed. This art work was esthetically pleasing because it did not have the high gloss and annoying reflectivity characteristic of conventional oil paintings produced on sized canvas with pigments suspended in linseed or similar oil. However, the very characteristic that is responsible for the pleasing effect is the source of a difficulty, as the painting exhibits virtually the same absorptivity and capillarity as the original canvas. Consequently, the paintings are easily soiled and are difficult to restore. The difficulty is even greater in the case of some paintings which had areas of unsized, unpainted canvas.

In contrast to the above type of painting, conventional oil paintings, which are produced on sized canvas with an oil that in time polymerizes and oxidizes, have a nonporous, impervious surface, which if soiled can be cleansed with water and a detergent. The surface of oil paintings can be protected by applying an alcoholic solution of certain resins, which when soiled or deteriorated can be dissolved off and reapplied as is already known.

At the present time no process or treatment appears to be known for producing protective coatings on unsized canvas, which would be impervious, invisible, and flexible; and, hence which could be applied to the new type of paintings without changing their appearance. The principal object of this invention is to provide a protective coating which would resist soiling from moist or greasy contacts, settling of dust or airborn contaminants, and damage by minor accidents or vandalism, such as pencil or crayon marks andwhich is capable of being easily removed with its contaminant and thus to permit a new coating to be applied.

This and other objects will become apparent or will be pointed out in the description which follows.

The protective coating capable of achieving the stated objective when applied to canvas should have the following characteristics:

1. It should be sufficiently impervious so as to prevent for about I minute the penetration of common liquids, like perspiration. moisture. liquor and oils. The expression semi-impervious in this specification means that the treated canvas prevents the passage of a drop of mineral oil (SAE No. 20) for a minute or more. In comparison, a drop of such oil placed on untreated canvas is adsorbed immediately.

2. It should be readily dissolved off without detriment to the painted surface and easily reapplied.

3. It should be virtually invisible, so as not to alter the appearance of the unpainted canvas or of the painting itself; for example, it should have no detectable gloss when viewed at a reasonably direct angle and should not be detectable at a viewing distance of about 3 or 4 feet.

4. It should be flexible. This property is necessary because the painting should be capable of being made into a roll for ease of transportation without the coating cracking.

5. The solution of the protective coating should be easy to apply. This requires that it be of a viscosity which permits the application of a thick layer without running and yet exhibits sufficient fluidity to level out before drying.

Conventional lacquers applied to the surface of canvas with a brush did not produce an impervious surface coating. Even successive applications of a lacquer did not make canvas proof against soiling. Consequently an evaluation of water soluble resins was undertaken.

The following procedure was used. The aqueous high polymer solution (which usually was quite viscous) was applied to a weighed specimen of canvas with an ordinary paint brush and the specimen allowed to dry overnight. The increase in weight was noted.

A series of soiling agents was then applied to the treated canvas, allowed to remain for about two minutes, and the excess wiped off. The soiled specimen was allowed to dry. The removal of the soil along with the resin was accomplished by alternately wetting and lightly sponging the surface of the canvas at intervals followed by occasional rinsing under a gentle stream of water. This cleansing process required about five minutes.

The soils applied to the coated canvas were of three different types: (a) commercial lndia inks of five different colors including black, which was probably an aqueous suspension of carbon; (b) marks made with an ordinary lead pencil and with a china-marking pencil, which left a waxy trace; (c) a suspension of raw umber in oil prepared according to a US. Federal Specification No. "IT-P-30b, Sept. 10, 1959. The suspension consisted of raw umber, 35 g; white petrolatum, 6 g; and mineral spirits, 40 g. This umber-soil was the most difficult to remove of the three. In those instances in which the raw umber penetrated into the interstices of the canvas, it could not be removed, even by intensive laundering with soap and water.

To confer protective action to canvas, it was found that the resins had to be applied in strong solutions of 8 percent to 15 percent by weight. Solutions below 8 percent by weight conferred inadequate protection. The more concentrated solutions of the resins were viscous, having a consistency like a table syrup or glycer- The canvas used in these evaluations had a weight of about 40 to mg per square cm. From the thickness of the canvas (about 0.75 mm) and this weight, it is calculated that the canvas was about 40 to 50 percent voids. The weight of resin which had to be present on one side of the canvas to protect it ranged between 4 and mg per cm This amount would be sufficient to fill only a fraction of the voids in the canvas.

While not wishing to be bound by any specific theory as to why certain water soluble resins are more effective than others, it appears that their effectiveness may be due to the formation of a semi-impervious coating on the surface of the canvas and not on the filling up of the interstices.

The water soluble resins which were found to impart some protective action against soiling of canvas included the following: ordinary glue or gelatin, polyvinyl alcohol, acrylic acid polymers, a number of cellulose derivatives, and natural gums. Of those, sodium carboxymethylcellulose in a 12 to 15 percent solution gave the best results. The effectiveness of sodium carboxymethylcellulose in protecting canvas against soiling should not be confused with its utilization in detergents, where it is used in low concentrations of 0.1 percent or less to prevent soil from resettling on fabrics during laundering. In protecting canvas, sodium carboxymethylcellulose (hereinafter designated as CMC) does not appear to function as a detergent as evidenced by the following experiment. Canvas (without any prior treatment) was soiled with the materials mentioned previously. The canvas was then heavily treated with CMC which was subsequently removed with water. The soils were not removed by this procedure, which, however, would have been the case if the protective action of CMC were due to detergency.

Furthermore, the action of CMC in protecting canvas does not appear to require the use of it in conjunction with wetting agents, as has been suggested in U.S. Pat. No. 2,986,471 which issued May 30, I961 on the treatment of impervious surfaces such as automobile bodies. In such a use, the wetting agent apparently assists removal of soil from a nonporous body through a lowering of the surface tension. However, in the application of CMC to canvas, the incorporation of wetting agents was found to be detrimental to the formation of the impervious film that serves as a barrier to soils.

As indicated above, in order to impart an appreciable resistance to soiling, canvas should be coated with sufficient CMC solution to provide 4 to 10 mg per cm of the resin on one side and double this amount if both sides of the canvas are treated.

Neither bare canvas nor unsized, painted canvas (painted with acrylic resins dissolved in organic solvents) exhibit any appreciable change in appearance or color when treated with these amounts of CMC. Furthermore, the treated surface does not have any appreciable gloss. Only by examining the surface at a glancing angle can the presence of a slight gloss be detected.

CMC is commercially available in a number of grades, the main difference being the viscosity of the solutions. For the purpose of protecting canvas from soiling, it is desirable to obtain the highest concentration of CMC in a solution of lowest viscosity in order that it can be readily painted onto a surface. A particularly preferred grade of CMC for the present invention was found to be CMC-7L1 manufactured by Hercules Incorporated.

The viscosity of the 10 percent solution of this grade of CMC ranged between 4,000 and 7,000 centipoises.

The viscosity of the 12 percent solution, which is the concentration found most suitable for treating canvas, ranged between 13,000 and 38,000 centipoises. The viscosity was like that of glycerine or a table syrup and no difficulty was experienced in painting this solution on a canvas surface. The viscosity of the 15 percent solution ranged between 90,000 and 180,000 centipoises, and this solution was found to be too viscous to apply readily. On a small scale the solution was prepared with stirring and the slow addition of CMC. Too vigorous stirring created a foam which was difficult to dissipate. Another procedure found suitable was to add the CMC in small increments to a container of water followed by stoppering and shaking vigorously by hand. There was formation of some lumps, but by shaking the container a few times each day over a period of a few days, these broke up and dissolved.

The solution of CMC is improved by some additives. The solution is attacked by mold and putrifies in several weeks. The addition of various stabilizers is often desirable as is known in the art. For example, the addition of phenol, about 0.5g per liter, to the CMC solution was found to prevent the putrification.

Another useful additive to the CMC solution is an optical brightener for the purpose of whitening the canvas, which usually has a yellowish cast that is slightly intensified by the CMC film. The optical brightener absorbs ultraviolet light and converts it into visible blue light which serves to neutralize the yellow tint of the canvas. One optical brightener that I have found suitable is TINOPAL 4MB/ 154, product of the Geigy Chemical Corporation. Since the brightener is only sparingly soluble in cold water, it should be dissolved in a small quantity of hot water and added to the main quantity of cold water just prior to adding the CMC. In the presence of the CMC the brightener did not precipitate out. The optical brightener is used in the CMC solution at a concentration of about 0.25g per liter. The optical brightener improved the whiteness of the canvas when viewed under daylight or fluorescent lighting, but there was no appreciable whitening effect under incandescent lighting. The brightener very slightly altered the color of the painted areas. This could be detected only by a side by side comparison.

Some variations of the CMC treatment were investigated. Lowering the pH of the solution to 3.5, which meant that the CMC was present as the acid instead of the sodium salt, did not affect the protective value of the film. The incorporation of glycerine in the solution to the extent of 15 percent of the weight of the CMC had no apparent effect on the protective value of the film. Glycerin would probably make the film more flexible. Treatment of a CMC film on canvas with a 10 percent solution of alum converted the CMC into a brittle, insoluble film. When this specimen of treated canvas was soiled as previously described, the soils could not be removed with water. This confirms the importance of the solubility of the CMC film for the cleaning process. In another variant of the application of CMC, a 5 percent solution was applied two or three times with drying in between each application. This process did not result in any improvement in protective action and the appearance of the canvas was less satisfactory than with one application of a 12 percent solution.

Canvas treated with CMC retains some flexibility. It can be slowly rolled around a cylinder 2 inches in diameter without cracking. A smaller radius of curvature causes cracking of the coating, which can be detected by moistening the surface with a mineral oil containing an oil-soluble dye. The flexibility of treated canvas is important, because on occasion a painting may need to be rolled for transportation.

The canvas used in the practices of this invention, when wetted, shrank about 0.5 percent. In contrast, the same canvas treated with CMC shrank about 3 percent. A strip of canvas, after treatment with CMC solution, was prevented from shrinking by application of a spring tension. The force amounted to a few pounds per linear inch of width of strip. However, there is no shrinkage of canvas if it is rigidly mounted in a frame prior to treatment with CMC solution and allowed to dry in the frame. I have found that canvas so treated and then cut out of the frame exhibited no appreciable shrinkage (less than 0.1 percent).

The shrinkage of canvas treated with CMC, or the tension generated if the shrinkage is prevented, requires some precautions in applying the CMC treatment to paintings if the frames are to be prevented from subsequently warping. The frame of the painting should be made rigid, for example by securing it with C-clamps to a table top or to a sheet of inch-thick plywood. A large painting may require clamping to a wall or floor. The CMC solution is then applied liberally with a good quality paint brush of as large a size as practicable (4 or 6 inch width), and the entire painting should be coated before any portion of the coating dries. It is helpful to view the moist surface at an angle to detect any areas that may have been missed. After the CMC has dried, the frame of the painting can be released from the clamps. The frame will be found to still be true and the painting taut as if recently stretched.

A painting need not be tightly stretched in its frame before treating with CMC solution, since it is found that slack areas as well as ripples disappear as the CMC solution dries. It is possible that the gradual drying of the CMC solution provides a more uniform distribution of stresses than that obtained in stretching a painting manually.

In this connection, paintings treated with CMC showed an unexpected benefit, in that they were not sensitive to changes in humidity and temperature, but maintained their tautness winter and summer. In contrast, untreated paintings on unsized canvas (painted with acrylic resins in organic solution) often developed large, unsightly ripples in cold dry weather owing to the expansion of the canvas. In hot humid weather the canvas shrinks and the ripples disappear. If the paintings are tightened in winter, then during the humid period it is possible that the canvas would be put under an undue strain. A painting, which had been treated with CMC, during an extensive test period did not undergo these cycles of slackness and tautness, but maintained a smooth. taut appearance and without warping the frame.

in treating paintings with CMC in accordance with my invention the following should be noted:

a. Only paintings on a frame should be treated. lf paintings are treated in the unmounted condition, the painting may not be capable of being subsequently stretched on a frame to yield a plane, taut surface, because the CMC coating makes the canvas less yielding.

b. If the CMC solution is also applied to the back of the painting, care should be taken to prevent the solution from oozing between the canvas and the wooden frame. If this is not done it is possible that after drying the canvas will be found to be glued to the frame and a line or crease may form in the canvas on the viewing side along the edge of the frame. One way to avoid this difficulty is to insert a strip of polyethylene between the frame and the canvas. The polyethylene strip is then removed after the CMC dries.

It should be noted that the 12 percent CMC treatment is applicable specifically to paintings produced with an acrylic resin dissolved in an organic solvent, which paintings have an absorptiveness somewhat akin to that of the unprimed, bare canvas. The application of the CMC treatment to paintings produced with the water-emulsion type of acrylic paint requires a slight modification in the procedure. This is because the emulsion is broken on the surface of the treated canvas, and, hence, the resin does not sink into the canvas as in the case of the organic type of acrylic solution. Consequently, the former type of paint yields a more impervious surface than the latter, but by the same token the former does not produce the pleasing, dyed or stained appearance of the latter. Because of the smaller absorptiveness of the emulsion type of painted surface, the liberal application of a thick layer of CMC solution may result in the production of glossy patches on the painting. To prevent this, either the CMC solution should be brushed on more thinly or a more dilute solution should be used, for example 8 or 10 percent, or a 12 percent solution of a related cellulose derivative hydroxypropylcellulose may be used. Although not as protective as CMC when applied over bare canvas, it provides satisfactory protection when applied over the emulsion type of painted surface. It has the advantage over CMC of forming a more flexible film and solutions of a given concentration have a lower viscosity than CMC solutions.

Although sodium carboxymethylcellulose (CMC) is the particularly preferred water-soluble resin for protecting the unprimed paintings, several other resins were found to be almost as good and still others had some protective action. However, protective action was not the sole criterion in establishing that a resin was satisfactory, as color, transparency, and flexibility were also important and a resin could be considered unsatisfactory on the basis of any of these properties.

For example, ordinary gelatin had good protective value, but the films were too brittle in the thickness required for protection.

Methylcellulose in concentrations of 10 to 20 percent yielded almost as good protection as CMC. The film had the advantage of being more flexible than CMC, but was slightly more yellowish in color. Removal of the raw umber soil from treated canvas was not quite as rapid or complete as with CMC.

Hydroxypropyl cellulose applied as a 15 percent solution, was not as protective as either CMC or methylcellulose.

Hydroxyethyl cellulose in 15 percent solution gave protection about equal to that provided by hydroxypropyl cellulose but had no advantages thereover.

Several noncellulosic water-soluble resins also yielded some protection to canvas, although not as much as the cellulose compounds already discussed. Polyvinyl alcohol (a low viscosity grade was used) in 10 to 15 percent solutions were moderately protective. India ink marks were not as completely removed as with the films of cellulosic derivatives. A disadvantage of polyvinyl alcohol was that to prepare the solution the compound had to be dissolved in nearly boiling water and similarly, the soiled films on canvas required hot water for most efficient removal.

Finally, for comparison with CMC, canvas was primed with gesso, (which consists of whiting dispersed in an organic solution of a resin) and then treated with various soils. The raw umber soil was fairly completely removed with soap and water, but the laundering did not suffice to remove the various India inks as completely as did rinsing of CMC coatings with water.

These results suggest that for priming canvas prior to painting artists might consider the use of aqueous solutions of CMC, or polyvinyl alcohol, or some of the other water-soluble resins, as alternatives to the timehonored materials glue or gesso. lf it is necessary to render the coating unattackable by water, polyvinyl alcohol can be insolubilized by treatment with a solution of formaldehyde and CMC with a solution of alum.

. It was originally assumed that the protection of canvas from soiling would require the filling up of the interstices by a resin. However, after some protective procedures were developed it appears that the protection of the canvas resulted from the presence of a semiimpervious film on the surface and not from the filling up of the interstices.

The semi-impervious nature of the protective film that is formed by solutions of CMC and the other protective resins is easily demonstrated by placing a drop of mineral oil containing an oil-soluble dye on the surface of the treated canvas. The drop is allowed to remain for about one minute and then wiped off. The dye will be found either not to have penetrated at all or at most only through a few pinholes. The penetration of mineral oil without any added dye can be readily detected by holding the specimen up to the light and noting the translucent areas. In contrast to the behavior of the protective resins, mineral oil placed on canvas treated with a conventional lacquer penetrates completely through the cloth within a few seconds.

. demonstrated by immersing the end of a strip of treated canvas in the oil dye solution. The latter will be found to have risen up into the interior of the strip, but without having penetrated to either surface.

To a first approximation, the protective value of the various surface films that were applied to canvas correspond with the observed resistance to the penetration of mineral oil through the canvas. One exception was the coating of polyvinyl alcohol. It was about as resistant to penetration as CMC films, but it did not give the degree of protection against India inks that would have been expected on the basis of the good showing in the test.

it has been found that penetration of the resin solution into the canvas is not required for establishing protection against soiling. A high viscosity type of CMC, which formed a gel at a concentration of percent, was plastered on canvas with a spatula and allowed to dry. The treated canvas had good resistance to soiling. A similar result was obtained with a l0 percent gel of agar-agar.

The protective action of CMC and other watersoluble resins is thus partially due to the existence of a relatively impervious film on the surface of the canvas.

It appears that two factors are mainly responsible for the formation of the protective surface coating namely: 1. restricted penetration of the solution into the canvas, and

2. formation of a gel, which has some tensile strength, early in the drying process.

Penetration of the solution into canvas is restricted by two properties of the solution, i.e., by the viscosity and the surface tension of the solution. The role of viscosity is illustrated by the behavior of a 10 percent solution of polyvinylpyrrolidone (PVP). The solution has a low viscosity compared to a solution of CMC and readily penetrates into the canvas, but it does not confer any protective action. By adding to the PVP solution only 2 percent of a grade of CMC that has the property of greatly increasing the viscosity of the solution, an appreciable protective effect was obtained, although the 2 percent addition of CMC, used by itself, conferred negligible protection. A similar result was obtained with the polyethylene oxide resin, which has no protective value by itself, and with a 2 percent addition of CMC. v

The surface tension of the solution prevents rapid penetration into the interstices of the canvas. This is because the presence of the trapped air in the fibers prevents a rapid wetting of the canvas. The low surface tension of organic solutions of resins compared to aqueous solutions may be one of the reasons that these solutions do not form protective surface films. When a wetting agent was added to a solution of CMC, the protective action of the resulting film on canvas was significantly inferior to that of the CMC solution without the wetting agent.

It is also possible the water-soluble resins form a portective barrier layer more readily than solutions of conventional lacquers because the water solution quickly turns into a gel after it becomes slightly concentrated by evaporation of a small percentage of water. The gel thus formed has a certain tensile strength and holds together as a film as it dries instead of slowly being absorbed into the interstices of the canvas, as would be the case for a nongelling solution.

Whatever the fine reasons for its effectiveness it is evident that the protective coating can prevent soiling simply by acting as a barrier layer. Another important protective feature of the surface layer is its capacity to swell when wet with water. This would slow penetration of aqueous soils into the interior of the canvas. It is also likely that the swelling of the film closes up the pinholes. The swelling of the CMC films may be the reason that they are more effective in preventing soiling by India inks (which are aqueous solutions) than by the raw umber-soil. Also, this is consistent with the observed better protection of CMC films against inks in comparison with polyvinyl alcohol films. A third characteristic of the resins is their ready removal with water along with the adsorbed soil.

It will be noted that the protection of conventional oil paintings was not evaluated because the surface of these are impervious and, at least theoretically, could be cleansed with water and a detergent.

Having now described preferred embodiment of the present invention, it is not intended that it be limited except as may be required by the appended claims.

What is claimed is:

l. A process for imparting a semi-impervious, invisible, flexible, protective, soil-resistant surface to canvas and to surfaces of unsized canvas painted with artist's acrylic-type of paint consisting of acrylic resin in organic solvent along with pigment which comprises applying to the surface of said canvas a viscous solution of water-soluble resins at a concentration of 8 percent to 20 percent by weight and permitting said solution to dry.

2. The process of claim 1 wherein the solution is applied by brushing.

3. The process of claim 1 wherein a soil resistant surface, such that the surface is not penetrated in one minute by an aqueous dye solution or by mineral oil, is produced on said canvasv 4. A process as set forth in claim 1 including in addition washing the surface with water so as to redissolve the resin which carries along with it soils present on said surface.

5. The process of claim 1 wherein the viscous solution is an 8 percent to percent aqueous solution of sodium carboxymethyl-cellulose, having a viscosity of 5,000 to 40,000 centipoises.

6. The process of claim 5 including the addition of phenol at a concentration of 0.5 g/l to the solution of sodium carboxymethylcellulose for the purpose of preventing the growth of mold on long time storage or the solution.

7. The process of claim 1 wherein the viscous solution contains 0.05 g to 0.5g of an optical brightener with a blue fluorescense per liter of the solution for the purpose of neutralizing the yellowish tint of the treated canvas and for making the latter appear whiter under daylight or under fluorescent illumination.

8. The process of claim 1 wherein the viscous solution is an 8 to 15 percent solution of hydroxyethylcellulose.

9. The process of claim 1 wherein the viscous solution is an 8 to 15 percent solution of hydroxypropyl cellulose.

10. The process of claim 1 wherein the viscous solution is a 10 percent to 20 percent aqueous solution of methylcellulose.

11. The process of claim 1 wherein the viscous solution is a water solution of a water-soluble cellulose derivative selected from the group consisting of hydroxy alkyl celluloses, carboxy alkyl celluloses, alkyl celluloses and alkali metal salts of said alkyl or substituted alkyl celluloses.

12. The process of claim 1 wherein the viscous solution is a 10 to 20 percent solution of polyvinyl alcohol in water.

Claims

1. A PROCESS FOR IMPARTING A SEMI-IMPERVOUS INVISIBLE, FLEXIBLE, PROTECTIVE, SOIL-RESISTANT SURFACE TO CANVAS AND TO SURFACES OF UNSIZED CANVAS PAINTED WITH ARTIST''S ACRYLIC-TYPE OF PAINT CONSISTING OF ACRYLIC RESIN IN ORGANIC SOLVENT ALONG WITH PIGMENT WHICH COMPRISES APPLYING TO THE SURFACE OF SAID CANVAS A VISCOUS SOLUTION OF WATER-SOLUBLE RESIN AT A CONCENTRATION OF 8 PERCENT TO 20 PERCENT BY WEIGHT AND PERMITTING SAID SOLUTION TO DRY.

2. The process of claim 1 wherein the solution is applied by brushing.

3. The process of claim 1 wherein a soil resistant surface, such that the surface is not penetrated in one minute by an aqueous dye solution or by mineral oil, is produced on said canvas.

4. A process as set forth in claim 1 including in addition washing the surface with water so as to redissolve the resin which carries along with it soils present on said surface.

5. The process of claim 1 wherein the viscous solution is an 8 percent to 15 percent aqueous solution of sodium carboxymethyl-cellulose, having a viscosity of 5,000 to 40,000 centipoises.

7. The process of claim 1 wherein the viscous solution contains 0.05g to 0.5g of an optical brightener with a blue fluorescense per liter of the solution for the purpose of neutralizing the yellowish tint of the treated canvas and for making the latter appear whiter under daylight or under fluorescent illumination.