1New, innovative solutions considering modern principles of restoring artworks have been developed recently in the field of conservation and restoration of paintings. We are grateful that the remarkable progress of the profession encourages the use of ethical principles in restoration, while the number of unsatisfactory procedures is declining and the general public’s awareness of the importance of preserving artistic heritage is growing. Unfortunately, however, available resources often dictate which materials are to be used. As a result, this affects the quality of conservation and restoration procedures, which must be carried out professionally and carefully to guarantee the physical, symbolic, historical and aesthetic integrity of the artwork.
- 1 Conservation–restoration work was carried out under the expert guidance of the Department of Easel (...)
2The main goal of the research and the subsequent intervention on the Baroque painting of Jesus among Teachers1 from the St. Trinity Church in Ljubljana was to rescue and stabilize the weakened woven support, to eliminate the holes and tears, and to prevent further deterioration. The focus was on two basic conservation–restoration principles: minimal intervention and reversibility.
3The painting was in a relatively poor condition before the conservation-restoration procedure. The supporting canvas was sewn together from two different pieces of canvas, which caused considerable damage to the paint layer, especially in the lower part of the painting, where the canvas was heavily creased in a vertical direction. The flakes of the paint layer pulled the insufficiently taut canvas along, so that a negative version of the cup form occurred on the front of the painting.
4The canvas was deformed and damaged in several places, while the damage to the painting had been inappropriately treated in the past.
Fig. 1 Jesus among Teachers, St. Trinity Church in Ljubljana
Front of the painting before and after the restoration procedure
Credits: © Andreja Ravnikar, 2011/2012
5Stabilization of the weakened support is employed in all procedures to reduce and stop the level of deterioration of the painting support. This can be achieved by minimal intervention or by lining the whole and thereby achieving structural coherence and consolidation of the support. Since local restoration is not always sufficient, it was necessary to line the whole with a thin non-woven fabric, which provides sufficient support to the original canvas and reinforces it with little weight added.
6The term reversibility has often been perceived in the wrong manner. It is difficult to attribute this designation to the materials applied to the painting during the restoration process, since in many cases they are not completely removable. But this term can be used to describe each of the procedures. Reversibility largely depends on the choice of suitable lining canvas or fabric, which governs the quantity of adhesive that needs to be applied. A suitable method is selected by taking into account the method and the strength of the joint between the original and the lining canvas, since the manner in which the adhesive will be activated is significant. When using adhesives reactivated by solvents, we need to consider the solubility of the materials within the painting as well as the materials that have been usedin previous procedures. Often overlooked is the criterion of quantity of the used material. Small quantities of adhesives are often easier to remove, and leave behind a minimal amount of residue in the interspaces and pores of the original canvas (Appelbaum 1987).
- 2 In 1978, Barbara Appelbaum introduces the concept of re-treatability.
7In recent decades, the principle of minimality in the conservation of artworks is becoming increasingly important, and inextricably linked with the principle of reversibility. Minding that any restoration process carried out is not completely reversible, a minimal intervention may therefore be the only way that will, to a maximum extent, maintain the integrity of an object without impeding any subsequent restoration (Appelbaum 1987).2
8To find the most appropriate lining method for the stabilization of the canvas, and because the painting will be returned to a relatively unstable environment after its restoration, a test was carried out on four samples similar by structure and composition to the original painting. The results of the test and their evaluation were of great assistance in making a final decision on the further treatment of the woven support.
9The mist-lining method was developed and presented to the public in 2003 by René Hoppenbrouwers and Jos van Och, Dutch conservators and restorers. In order to stabilize the canvas support of large format paintings, they proceeded from Mehra’s cold lining method and the use of synthetic adhesives (Van Och and Hoppenbrouwers 2003).
Fig. 2 Two application methods
Spraying (left) and applying through a sieve in dots (right).
Credits: © Andreja Ravnikar, 2011
10The other more classical method was the nap-bonding method, which was developed by Vishwa Ray Mehra and in which adhesive is applied as small glue spots to the canvas (Mehra 1975).
11Both were carried out following the basic principles of minimal intervention and reversibility. The two methods employ little adhesive, creating less impact on the canvas, physically as well as chemically, and also facilitate subsequent removal of the lining canvas. Both methods were carried out on different materials – on a classic synthetic canvas Lascaux Polyester Fabric P110 and on a very thin, non-woven fabric.
12A synthetic canvas commonly in use is quite resistant to the effects of the environment (humidity, temperature), microorganisms and, because of its properties, one of the options when choosing a suitable lining fabric. As an alternative and because of its composition (34% cellulose and 66% polyester), a thin, semi-synthetic, non-woven fabric with the commercial name TNT 54 was chosen. The percentage of cellulose fibres of the basically synthetic fabric in combination with polyester fibres forms a stronger, less absorbent and more flexible fabric suitable for the relatively unstable environment (Richards 1984).
Fig. 3 Cross-section of the fabric support
The canvas (left) and non-woven fabric (right) with the upstanding nap.
Credits: © Andreja Ravnikar, 2011
13For both lining methods – mist-lining and nap bonding – two different acrylic adhesives were used. Plextol B 500, used for nap-bonding, is an agent with excellent adhesive strength that can be activated without increased temperature. When thickened, it becomes more viscous which at least partially prevents absorption into the original layers of the painting before the substance is polymerized.
14A mixture of adhesives Dispersion K 360 and Plextol D 540 was used for mist-lining. By mixing these two components, the pH value alters to slightly acidic (pH 6), which does not correspond to a neutral or even slightly basic pH value. Therefore, the pH value was adjusted to pH 7 by adding alkaline sodium hydroxide solution by drop.
15For comparative purposes, two application methods were used on the samples: the nap-bonding and the mist-lining method.
16In nap-bonding method a thickened adhesive is applied through a sieve in points evenly distributed on the surface of the lining canvas. Application through a sieve ensures consistency and minimal application of the adhesive with no additional moistening, and the lining canvas is easier to remove (samples 1/B and 2/B).
17The mist-lining method is one of the alternative methods in which adhesive is sprayed to the upstanding naps of the lining fabric (samples 1/A and 2/A).
18In the preparation stage of the mist-lining method, the non-woven fabric was stretched onto a temporary wedge stretcher that was slightly larger than the painting. The stretched fabric was gently roughened on one side with sand paper in three different directions to increase the nap surface. This created a layer with greater surface area to which the adhesive was later applied.
19The adhesive was evenly distributed on the raised fibres in three layers using a high-transfer efficiency spray gun. Each layer was left to dry before the next layer was applied. The adhesive thus enveloped the individual fibres, maintaining the fabric’s elasticity, while at the same time allowing for successful reactivation of the adhesive from the back due to its permeability. Since the adhesive is kept on the surface only, it does not penetrate deeper into the structure.
Fig. 4 Non-woven fabric after adhesive application
Adhesive enveloped individual upstanding fibres
Credits: © Andreja Ravnikar, 2011
20The lining fabrics, onto which the adhesive was applied in dots (samples 1/A and 2/A), were glued to the canvas using the solvent reactivation method. Xylene sufficiently softened the adhesive so that it became sticky again. After both canvases were put in place (lining front side up), the adhesion procedure was carried out in a low-pressure table. After 15 minutes, the sample was removed from the low-pressure table.
Fig. 5 Reactivation of the adhesive layer in an airtight chamber
Two samples were placed into the low-pressure table, one front side up and the other inversely.
Credits: © Andreja Ravnikar, 2011
21In the mist-lining method the adhesive was reactivated with ethanol vapour (through a cloth moistened with solvent) from the back of the non-woven fabric in an improvised, airtight chamber. When the adhesive layer became sticky enough, the moistened cloth was removed from the chamber, as well as the lower layer of Melinex, which allowed for free air flow whilst pressing the layers together. Consequent resealing of the low-pressure vacuum table and the regulation of pressure enabled the two canvases to merge, and established adhesion. The sealing was removed after 45 minutes, and the sample was left in place until it stabilized and the solvent fully evaporated.
22Prior to and after simulation of the lining, the weight of individual samples was measured (canvas, fabric, adhesive), listed, the amount of used adhesive was calculated, and an attempt to remove the lining canvas / non-woven fabric was made.
Fig. 6 Table 1
T – nap-bonding method, M – Mist-lining method, Synt. – synthetic canvas Polyester Fabric P110, NT – non-woven fabric TNT 54
Credits: © Andreja Ravnikar
23The table shows that, in comparison with nap-bonding, the mist-lining method applies a considerably smaller quantity of glue. The quantity of adhesive required is also influenced by the selection of canvas or lining fabric. A combination of unwoven fabric TNT 54 and the mist-lining method (sample 2/B) required a minimal quantity of adhesive (2.6 g or 2.2% in weight) per sample, which means that the quantity of adhesive used was approximately 6 times smaller than in the sample where adhesive was applied in dots onto a synthetic woven fabric (sample 1/A). This information is particularly important when lining paintings with a thin, sensitive paint layer and an extremely thin and unstable support, where any excess weight of added material could cause additional damage (flaking of the paint layer, tautness of the canvas ...
24In practice, two methods of removing a canvas from the back of a painting are generally used. The canvas may be removed (of course at the smallest possible angle) diagonally in one piece, or it may be slit and then gradually removed in ribbons. The latter is more suitable for larger paintings.
25After completing the lining of samples, I manually observed, by partly removing the canvas or lining fabric, how much strength was required for removal, how strongly the bond formed by the adhesive used in combination with a specific canvas or fabric, as well as the effectiveness of removal. For our needs, a good bond means a bond that requires the least force to still hold the two layers together. If the adhesive or bond were too strong, the removal of the canvas lined in such a way would represent a heavy burden for the painting.
Fig. 7 Microscopic examination
Residues of adhesive on lined canvas samples.
Credits: © Mateja Vidrajz
26The removal of lined canvas / fabric on the samples was performed manually. This may be facilitated by partly softening the intermediate adhesive layer with an adequate solvent. Before carrying out this procedure, the solvent should be tested on a coloured layer and observed for any changes. For the procedure of repeated adhesive reactivation, solvents that are least harmful to health are selected or adequate protective means are used.
27More detailed findings of the canvas removal attempt on individual samples are presented in the following table:
Fig. 8 Table 2
Mist-lining method in combination with the non-woven fabric TNT 54 gave adequate results.
Credits: © Andreja Ravnikar
28Both lining methods proved satisfactory compared to the traditional methods and adhesives used for lining. Adhesive consumption was extremely small, its quantity in the mist-lining method being significantly reduced. The tests showed that the lining could be almost completely removed, which is one of the objectives of the lining itself. The strength of the support to the painting and the adhesive bond can be regulated using different fabrics. Synthetic canvases do also adhere well to the original surface of the canvas due to their raised fibres, but leave fewer remnants behind when removed as the fibres are more firmly attached to the fabric: the threads of the synthetic canvas are in fact strongly attached to the original canvas and more strength is required to remove it.
29After all the tests were performed, we decided to use the mist-lining method in combination with the non-woven fabric TNT 54 on the Baroque painting. The sample simulations were of great assistance in selecting a suitable lining material.
30The selected lining fabric simultaneously protects the back of the painting from dust particles and also represents a kind of bridging between the original canvas and the subsequently added ribbons on the edges of the painting, which will facilitate mounting on a stretcher. Due to its tension properties, the fabric itself does not allow for independent tightening onto the stretcher, as too much elongation would quickly tear the fabric.
31The lining procedure for the Baroque painting was performed in the same manner as in sample 2/B. After preparation of the lining fabric, the adhesive was evenly sprayed onto the surface and the painting was placed into the low-pressure table front side up.
Fig. 9 Preparation of non-woven fabric for mist-lining
Roughening with sand paper and adhesive spraying.
Credits: © Andreja Ravnikar, 2012
32To ensure greater transparency during the process, the preparation of the table was adapted and individual layers were placed inversely in such a manner that a cloth moistened with solvent was placed underneath the painting itself. When the solvent vapour penetrated through the non-woven fabric and activated the adhesive layer, the cloth was removed.
Fig. 10Mist-lining with front side up
Positioning of the individual layers in a low-pressure table
Credits: © Andreja Ravnikar, April 2012
33After the mist-lining procedure was completed, the original canvas of the painting, along with the structural damage, was stabilized in a rather non-invasive manner. The joint between the two fabrics was extremely light, but nevertheless strong enough to provide sufficient support for the damaged painting. The input of the adhesive was limited to a minimum, ensuring high, if not complete, removability of the lining fabric from the original canvas.
Fig. 11 Mist-lining of a Baroque painting
Mist-lining in a low-pressure table.
Credits: © Tina Istenič, 2012
34The adhesive-spraying method respects the physical properties of the original canvas and maintains its open structure, providing an elastic bond between the original canvas and the lining canvas.
35The reactivation of the adhesive does not require an increased temperature, which, in some cases, presents a great burden to the picture layer. The selection of the lining fabric or canvas also defines the final weight of the lined painting, which, in this case, was just slightly increased.
Fig. 12 Mist-lining results
Backing before and after mist-lining in sidelight exposure.
Credits: © Andreja Ravnikar, 2011/2012
36Even though lining is a procedure that will not be fully visible to the subsequent viewer, it needs to be carried out in the most precise and professional manner, taking into account the compatibility of materials used and certain precautionary actions before the beginning of the actual procedure.
37The lining canvas should not in any way affect the adhesion and cohesion forces between the picture layer and its original support. Larger amounts of adhesive between the original and the lining canvas can affect the elasticity of the painting, which may become rigid and unresponsive to the natural forces within.
38All these factors are crucial when choosing the appropriate lining method. We should be aware that our decisions may be of significance to our descendants, who will be tackling similar problems and seeking appropriate solutions with the same desire to preserve artworks. It is or duty, when it comes to lining paintings, to make the removal of added materials as easy as possible, which the mist-lining method certainly allows.
39Despite numerous positive features of mist-lining, it is necessary to also mention some disadvantages or characteristics which require special attention. Reactivation of the adhesive with polar solvents could affect the paint layer or only specific pigments. Before the reactivation the adequacy of solvent in all colour areas must be examined. In case of over-sensitivity a different method not involving solvents must be chosen.
40Mist-lining method was developed specifically for the purpose of cold lining of large-format paintings in combination with vacuum envelope, but it is necessary to be an experienced professional for its successful execution. Independent handling with large-format paintings is almost impossible, often making it necessary to seek other people’s assistance. Additionally, all tools should be thoroughly prepared before the procedure, since the individual stages of the lining follow one another in quick succession.
41Although Van Och’s approach to lining paintings leads to the contemporary manner of minimalism and reversibility and opens many new possibilities, it will still take some time to change our sometimes passive attachment to established lining methods.