SE414895B - PROCEDURE FOR DISPOSAL OF ORGANIC MATERIALS IN RESTORING OIL PAINTINGS - Google Patents

Description

Non-aqueous binders, such as waxes and resins, have also been used.

An oil painting thus often contains up to about 80% or more organic substances, which in the presence of water can form substrates for fungi and bacteria. During growth, fungi and bacteria often develop enzymes, which break down various organic materials.

In previous restorations, oil paintings have often been provided with a layer of varnish, which over time has yellowed and spoils the appearance of the painting.

When restoring paintings, it is necessary to remove previously made duplicates and overpaintings, which work is often extremely difficult, due to the fact that the remaining original parts of the painting are very fragile and easily damaged further by solvents and mechanical forces during removal. especially of pasted duplicates.

The paint layer is usually protected by applying a wax layer and a cohesive paper to the image side of the painting when working with the back side. Then glue as much as possible to dissolve and remove the duplication. During this time-consuming work, the paintings are often further damaged.

Thus, there is a need for new methods to improve the technique of removing organic material from oil paints.

According to the invention, it has been found possible to remove organic material by enzymatic means by first determining non-specific enzyme activity present in the organic material quantitatively and inhibiting it by inhibition, suitably a competitive inhibition.

A competitive inhibition is obtained when the enzyme is added to an inhibitor substance which blocks the enzyme by competing with the normal substrate. The degree of inhibition can be determined by observing changes in Michaelis constant, Km, after the addition of inhibitor. Míchaelis constant is measured by observing the amount of reacted material per unit time and substrate concentration and entering these values in a Lineweaver-ßurk diagram. Values are plotted by V1 the amount of reacted material per unit time, plotted as å on the y-axis and substrate concentration, Esj, as -3> - on the x-axis1n. The straight line formed thereby intersects the [S] x-axis at a distance from the value x = o which corresponds to the value å fi, from which thus Michaelis constant, Km, can be determined.

The constant Km represents the substrate concentration that leads to a reaction rate that is half as large as the reaction rate at infinite substrate concentration.

The competitive inhibition in the material to be removed takes place by changing the Km value so that it rises to a high value. The simplest way to determine changes in the Km value is a polarographic examination of suitably triggered A material, such as lead (II) ions or any constituent amino acid or the like. A high Km value is then indicated by the fact that no release of said substance is obtained. The inhibition can take place with, for example, cysteine or another substance that inhibits snzymvdrkan. Each substance selected depends on the enzyme contained in the layer.

One skilled in the art can easily select a suitable inhibitor substance. Other types of inhibitors can also be used. An example is a non-competitive inhibitor with heavy metals such as lead, cadmium or mercury. In a polarographic examination, it is not possible to distinguish which inhibition method is used. This can be done by setting up a Lineweaver-Can chart. in non-competitive inhibition, as is well known, the Km value does not change, only the value for% at x = o.

It should be understood that by inhibition of enzymatic activity is meant only those enzymes which can interfere with the subsequent enzymatic treatment.

After the inhibition, an aqueous slurry of an enzyme selectively acting on the organic material is added, which is immobilized by adsorption to a carrier or entrapped in a gel, in such a way that the intended enzyme lysis can be carried out for a period of 10 minutes to 3 minutes. hours. The support can consist of solid materials such as silica gel, glass beads, activated carbon, membrane filters or ion exchange substances. The carrier may also be a gel, such as a polyacrylamide gel, carboxymethylcellulose or the like. The enzyme is then immobilized with a water-insoluble compound such as carboxymethylcellulose, a copolymer of ethylene and maleic anhydride, porous glass, poly-p-amine styrene, SephqrOs (after activation of BrCN), p-aminobenzoecellulose. The person skilled in the art can, after consultation with available literature, determine which enzymes are suitable for the particular organic material to be removed, and which carriers are suitable by simple experiments. Among the enzymes that can be used are lyases and hydrolases, such as carboxyl ester hydrolases, phosphomonoesterases, phosphodiesterases, glucoseidases, N-glycosidases, aminoacyl peptidases, peptidylamino acid hydrolases and proteinases. Among these, a variety of enzyme preparations are commercially available, such as u-amylase, β-amylase, carbonic anhydrase, carboxypeptidase, chymotryfosinase, β-glucosidase, catalase, lipase, papain, pepsin, proteinase, trypsin, pronase and urease.

Once an enzyme has been selected for the composition of the organic material to be removed, it is added to a suitable vehicle for immobilization. It is essential here that the enzyme and carrier be selected so that the organic material to be removed dissolves and is allowed to react within a period of 10 minutes to 3 hours. During restoration work, an effect time of about 1 hour is usually preferred. Because the enzyme is bound to a carrier, a suitable difference between liquid diffusion in the organic material and enzyme diffusion can be obtained. The concentration of enzyme may be higher and the course of the reaction may be more easily controlled.

In some cases it is also possible to work in liquids other than water, ensuring that the enzyme preparation has a greater affinity for the carrier than for the liquid. At high substrate concentrations, substrate inhibition is obtained, which is shown in a non-linear sequence of the values in a Lineweaver ~ Burk diagram.

It will be clear to those skilled in the art that such variables as temperature, hydrogen ion activity, must be adjusted with respect to the chosen enzyme-carrier system. How these variables are to be varied is stated in manuals and textbooks in enzyme chemistry.

After the enzyme-carrier system has been allowed to act for a calculated time, the organic material which has undergone enzymatic treatment is removed from the remaining material in the oil painting.

This is conveniently done by washing or tearing off textile materials after glue and glue have been enzymatically decomposed. The remaining material is finally subjected to treatment with the intention of irreversibly inhibiting any remaining enzyme residues. Sublimates, cyanides and other cytotoxic drugs and known inhibitors were used.

In many cases, paintings in previous restoration work have been provided with several layers, often of completely different origins.

It may therefore be necessary to select different enzymes for some of the layers and even to dissolve and remove one layer at a time with special treatment liquids for each layer, each selected after an analysis of the kind indicated above.

In the above description, reference has been made to polarographic analysis, but it is obvious that there are a number of different analysis techniques that allow analysis of substances released by enzymatic lysis. Photospectrography, chromatography and A7e119s1-s (II 10 15 20 25 30 35 electrophoresis can thus be used.

EXAMPLE An oil painting from the 17th century, which was restored several times and about 50 years ago was fitted with a pasted textile layer, was restored in the following way.

The restoration began by removing an overpainting and an underlying varnish layer by enzyme treatment. The enzyme present in the layer was inactivated by competitive inhibition, whereby in a polarographic analysis it was determined that the surface requires a coating with a solution containing 3 g cysteine per liter for total inhibition of enzyme activity present in the layer. The overpainting consisted of a varnish based on egg white, casein with pigments of yellow ultramarine, paris blue and a more pigment-containing layer containing egg white, casein, oil and as pigment lead white, zinc white, chalk, ocher, cadmium yellow, cadmium red, cobalt black pigment and carbon black.

After the inhibition, samples were taken on the grind mixed with casein in a phosphate buffer at a pH of 7.4 and at a temperature of 40%. No enzymatic activity could be observed after 10, 20 and 30 minutes, respectively.

To prevent the enzyme preparation from penetrating the paint layer and into the fabric, an insulating layer was created by wetting the fabric from the back with a non-solvent for the enzyme solution. A mixture of white spirit, toluene and ether was used as the insulating layer. The amount of insulating liquid was monitored polarographically during the course of the enzyme treatment.

Then a phosphate buffer solution containing 4 g / l pronase E, polyethylene glycol (molecular weight 1000) with a pH of 7.4 and a temperature of 25% was applied. The enzyme in the solution is immediately added to the polyethylene glycol which forms a gel in the buffer solution. A suitable area (approx. 0.25 m2) on the board was ironed with a brush with said solution.

The appropriate time for the enzymatic treatment was also determined by polarographic methods, in this case by determining released albumin. The half-stage potential for triggering albumin is -1.5 V.

The said solution was allowed to act on the overpainting and the varnish layer for about 50 minutes, after which the light products could be removed by washing the surface with turpentine, whereby further enzymatic reaction was also interrupted.

The remaining paint layer was applied with a thin wax layer (wax dissolved in turpentine) and a paper layer so that the paper adhered to the wax layer after which the board was turned and the duplication was treated in an analogous manner to the overpainting.

First, the chemical composition of the adhesive used was determined. This turned out to consist mainly of bone glue containing honey and a coarse linen fabric was used as the textile layer. Due to the fact that the board was stored in an environment with occasionally very high humidity (f ~ 100%), severe damage due to microbial growth had occurred in the board. The enzyme activity created by microbial growth was determined by polarographic means and the type of adhesive was also analyzed by polarographic ausorptlonal analysis, to determine the natural structure of the peptide chains. It was then determined that an enzyme preparation consisting of trypsin adsorbed on silica gel in a phosphate buffer with a pH of 7.4. After the preparation had been allowed to act on the duplication for 20 minutes, it could be removed without further damage to the original material. The treatment was repeated 3 times, whereby all residues of the adhesive layer could be removed.

After removal of increasingly added material, any remaining enzyme residues were irreversibly inhibited.

Thereafter, the board was restored in accordance with professional methods by applying suitable supporting materials and, 7811951-s repairing damage to the paint layer and applying new protective varnish over the paint layer.

The method can of course also be used in the restoration of paintings on wooden panels, painted furniture and on such occasions it is desired to remove enzymatically soluble organic layers from a substrate in general, although this is described with reference to oil paintings preferably on canvas.

Claims (8)

10 15 20 25 30 '7811951-8 PATENT REQUIREMENTS A method for removing organic materials in the restoration of oil paintings, characterized in that non-specific enzyme activity present in the organic material is quantitatively determined and inhibited by inhibition, after which an enzyme preparation capable of dissolving said organic material is applied and allowed to act and which enzyme preparation is bound to a carrier in such a way that the time for lysis of the organic material is between 10 minutes and 3 hours, after which lysis products are removed and the remaining material in the oil painting is subjected to an irreversible inhibition of any remaining enzyme residues. Method according to claim 1, characterized in that the inhibition made before the enzyme treatment takes place by competitive inhibition of non-specific enzyme activity. 3. A method according to claim 1, characterized in that the inhibition made before the enzyme treatment takes place by non-competitive inhibition of non-specific enzyme activity. A method according to claim 1, characterized in that multilayer organic materials are removed by using different, each layer suitable enzyme preparations, after which the light products are removed between each treatment with different enzyme preparations. 5. A method according to claim 1, characterized in that further enzymatic destruction of the oil paintings is stopped by an irreversible inhibition of all remaining enzyme activity after all the desired organic material has been removed. 6. A method according to claim 1, characterized in that polyethylene glycol is used as a carrier for the enzyme preparation. 7. A process according to claim 1, characterized in that silica gel is used as a carrier for the enzyme preparation. ® Process according to Claim 1, characterized in that Sepharos is used as a carrier for the enzyme preparation. '7811951-8 SUMMARY A procedure for removing organic materials in the restoration of oil paintings. In the process, any non-specific enzyme activity present is first determined quantitatively, after which this activity is inhibited. Thereafter, the organic material is enzymatically dissolved with an enzyme preparation suitable for the particular organic material to be removed. The enzyme preparation is supported on a carrier by adsorption or entrapment in a gel. Thereafter, dissolved material is removed and any residual enzyme activity is irreversibly inhibited. The method is suitable for removing layers of varnish and overpaintings as well as adhesive layers when doubling textile backgrounds in oil painting.