Johanna Nilsson, Evaluation of Stitched Support Methods for the Remedial Conservation of Historical Silk Costumes, e-conservation Journal 3, 2015
Available online 17 September 2015
Evaluation of Stitched Support Methods for the Remedial Conservation of Historical Silk Costumes
Different textile conservators tend to favour different techniques, mostly according to personal preferences or habit, since there are few empirical studies of the methods’ properties. This study investigated how three methods, using different stitching techniques and supporting layers, uphold the maximum force at break of silk samples. The samples were artificially aged, damaged either by cutting a slit to mimic a tear or by abrasion to simulate wear and then subjected to conservation. The studied methods were: securing the damage to a support fabric with laid couching stitches; securing the damage to a support fabric with spaced brick couching; and covering the damage with silk crepeline attached with running stitches. The tensile properties of the surrogates were evaluated after cumulative treatments: conservation, accelerated wear and finally conservation removal. The results show that after conservation, laid couching made both surrogates with tear and with abrasion the strongest though brick couching made surrogates with tear almost as strong. After accelerated wear, the surrogates with tear and laid couching as well as with brick couching were still stronger than the ones with crepeline. After the conservation was removed, however, crepeline in objects with abrasion gave the strongest surrogates of the methods. Laid couching took the longest time to execute and brick couching the shortest. Knowing the properties of different techniques should help in choosing the method that best suits the unique circumstances of each object; for instance, crepeline could be the method of choice when treating much degraded, fragile silk.
Historical costumes play an important role in the collections of many museums worldwide. They are exhibited to reflect a country’s history, a society, traditions and ceremonies or a single person’s story. It is important that we can preserve these costumes for the future. When preserving historical textiles, remedial measures are taken to support a fragile and damaged fabric in order to make it last longer by making it stronger. Remedial conservation methods for the preservation of textiles that use stitches in combination with fabrics have not previously been the object of an experimental investigation. Different materials and stitching techniques employed are described in literature, often as case studies, although the long-term success of such treatments has not been systematically examined [1-2]. However, there are some retrospective studies [1, 3-5], evaluating how the conservation treatments and the objects have withstood time and both Reeves  and Himmelstein  specifically discuss stitching used in textile conservation. Sahin et al.  tested a common engineering approach, tensile testing of mechanical properties in textiles, to study how this method can be used in order to understand how the affect of preservation on tapestries. Asai et al.  analysed how different supports influence the extension and deformation of tapestry surrogates in order to see how the support methods affect large hanging textiles. Several surveys have studied the use of adhesive treatments in textile conservation [8-10] and some report specialised methods such as fibroin-EGDE to consolidate fragile silk . The explanation of the lack of systematic studies of stitching technique may be that stitching is a traditional method that has been used for many years and is regarded as generally harmless and reversible even though this has been questioned by a few [3-4], whereas the non-traditional use of adhesives on textiles has raised concerns in what has been a more conservative conservation specialisation .
The most common types of damage occurring in silk costumes, making it necessary to conserve them, are frayed surfaces due to abrasion caused by repeated frictional contact over time and rips or tears resulting from sudden movement of a degraded, fragile fabric or because the silk is weighted. Although fragile, many historical costumes are in any case displayed in exhibitions and are lent to museums around the world. This leads to unavoidable handling before and during transport, during mounting on mannequins for display and photography. This handling further weakens an already degraded material even if it is conserved.
When deciding whether and how a costume should be conserved, it is important to have an informed idea of both the short- and long-term outcome. Various stitching methods in combination with a fabric continue to be the most common physical stabilisation techniques in textile conservation. Therefore, it is important to examine and evaluate their preserving effect, their durability and the potential damage they may cause to museum textiles. Moreover, in an era of cost cutting it is also important to document and compare the time needed to execute the treatments.
The main goal of this study is to assess how three selected conservation methods, commonly used in the conservation of historical costumes, affect the strength of surrogates for historic silk by determining maximum force at break. The surrogates are artificially aged silk samples that have similar fragility to the silk fabric in authentic 17th century silk costumes and are intentionally damaged by tear or abrasion . How the strength is affected in the damaged and conserved areas when subjected to accelerated wear, corresponding to many years of handling is also studied. The study also investigates how the conservation methods affect the surrogates by comparing them with each other after the conservation has been removed following accelerated wear. Included in the study is also a comparison of how long each method takes to execute.
2. Selection of Textile Conservation Methods
To establish which conservation methods are most commonly used in the preservation of costumes, and therefore important to evaluate, the popularity of various conservation methods was assessed in a questionnaire-based survey. The questionnaires were sent to textile conservators in Europe and North America . Furthermore, conservation reports describing the conservation at the Abegg Foundation (Switzerland) of 23 predominantly silk costumes from the early 17th century were studied. All conservation reports (a total of 819) concerning the conservation of costumes at the Royal Armoury in Stockholm from the 1890s and onwards were also studied.
In all instances, the most common method used is to lay the fragile textile on top of a support fabric placed aligned with the fabric grain and to then secure the damage with laid couching onto the support fabric. Laid couching is a long straight stitch, laid in line with either the warp or weft of a fabric and then fastened in place with short perpendicular holding stitches, inserted at regular intervals (Figure 1A) [1, 14]. Another common method is to protect a damaged and frayed area by a covering layer of silk crepeline that is attached to the fabric with running stitches along the edges of the crepeline (Figure 1B). Usually, when used on costumes, the shape of the crepeline is adapted to be able to fix it along its edges at existing seams or lines in the fabric. When a piece of crepeline covers a larger area it is common to further attach it with spaced rows of running stitches to keep it close to the underlying fabric to avoid bagging or wrinkling in the crepeline. A third method was used on several major conservation interventions at the workshop of the Royal Armoury in Stockholm on costumes with fabrics of plain silk or silk in combination with metal wires, flat strips or wool. The fragile textile is laid on top of a support fabric that is placed aligned with the fabric grain and the damage is secured with brick couching of various spacing onto the support fabric. Brick couching is a short stitch laid perpendicularly over one or several warp or weft threads sewn to form a regular pattern like brick-work (Figure 1C). Brick stitch is described by several authors [15-17] as a technique commonly used in tapestry conservation; warp couching and couching are also mentioned as stitches used in tapestry conservation and they are related to brick couching. Based on the survey and the consulted treatment reports it was decided to evaluate and compare three methods: method 1 (M1) - a damage is secured onto a support fabric with laid couching; method 2 (M2) - a damage is secured onto a support fabric with spaced brick couching; and method 3 (M3) - a damage is covered with silk crepeline which is attached with running stitches. To see how the methods were carried out for this study watch the film “Stitched support methods using laid couching, brick couching and crepeline attached by running stitches”, https://www.youtube.com/watch?v=eoogh96C7eI .
Artificially aged silk specimens to be used as surrogates for 17th century silk were exposed to cumulative experimental treatments in four steps: mechanical damaging, conservation with three methods (M1 laid couching, M2 brick couching and M3 crepeline), accelerated wear, and removal of the conservation. After each step, the maximum force at break of the surrogates was determined.
Preparation of the specimens and surrogates and the conservation interventions were carried out by the author and her colleagues at the Royal Armoury’s workshop in Stockholm. The abrasion, accelerated wear and tensile testing were carried out at an accredited research institute, Swerea IVF AB and the work was executed in cooperation between the author and one of the company’s textile engineers.
Standard silk fabric ISO 105-F06:2000 Bombyx mori was selected for the silk fabric to be investigated in this study, both for the specimens and for the support fabric in M1 and M2. Silk crepeline was used as cover in M3. The stitching in all three methods was performed with double-ply silk thread (supplied by Silke-Annet) using a Milward beading needle No. 15.
Circular specimens (160 mm in diameter) were stamped out of the standard silk fabric (size and shape of specimens chosen to conform to testing requirements of the Martindale abrasion system). Rectangular specimens (120 x 200 mm) were cut with the longer length in the warp direction. A total of 60 specimens were stamped for each shape.
3.2.1. Accelerated Ageing
Prior to ageing, 55 silk fabric specimens of each shape were dried in a desiccator over silica gel until the relative humidity was stabilised at 4% . They were then suspended in 1000-mL borosilicate glass bottles using the screw-top polypropylene caps to secure the suspending thread that was attached to the circular specimens so that they hang vertically in the warp direction. The rectangular specimens had a similar thread attached at one of their short ends. To the bottom of each bottle 42 g calcium chloride (CaCl2) was added to maintain a low relative humidity. Ageing was undertaken in two different cycles due to the limited capacity of the available oven, a Termaks TS 7472. The specimens were aged for 42 days at a mean temperature of 125ºC. The ageing method, thermo-oxidative ageing, was developed earlier by Nilsson et al. .
Two types of damage, a tear or an abrasion were created on the aged surrogates to make them similar to historical textile objects in need of conservation. Physical harm caused naturally is normally more complex than this with a combination of different damages but simplification was necessary. In the centre of each rectangular surrogate a tear was made by cutting a 50 mm long slit with a scalpel in the weft direction (Figure 2A). On the circular surrogates a frayed surface was created by abrasion according to SS-EN ISO 12947-2:19991 using the Nu-Martindale abrasion apparatus (James H Heal & Co Ltd) at a pressure of 12 kPa (Figure 2B). The resulting damaged area was 80 mm2. The abrading process was discontinued when the surrogate was clearly frayed and holes had developed. This occurred between 141 to 1004 rotations with an average of 418 turns per surrogate. The aged surrogates were degraded by either tear or abrasion, 50 of each kind.
3.2.3. Securing the Damage in M1
A support fabric 95 x 95 mm was centred and aligned under the damaged area of the surrogate, the 50 mm long slit and the 80 mm2 abraded area respectively. The support fabric was secured with c. 1 mm long running stitches on the face side and c. 5 mm long running stitches on the reverse close to its edges giving a total of c. 150 needle insertions.
The damaged area of the surrogate was secured with laid couching. On average 11 vertical long stitches with c. 7 mm spacing were sewn over the damage, the length of the stitches adjusted to the damage. Perpendicular stitches c. 1 mm long with a spacing of c. 4 mm were sewn over the long stitches. The vertical long stitches on the surrogates with tear were by turns c. 25 mm and c. 20 mm long (Figure 3). The length of the vertical stitch on the surrogates with abrasion varied depending on the damage shape (Figure 4). The amount of needle insertions for the surrogates with tear is c. 320, and for the surrogates with abrasion c. 600 (including the 150 needle insertions for the attachment of the support fabric). This method was carried out on 15 surrogates of each type of damage.
Left to right:
Figure 1. Examples of common stitches used in textile conservation: laid couching (A), running stitch (B) and brick couching (C). Illustration by Isak Nilsson.
Figure 2. Aged and damaged surrogates before conservation: surrogate with tear (A) and surrogate with abrasion (B). Photo by Östen Axelsson.
Figure 3. Surrogate with tear, conserved with M1. A support fabric is centred under the tear and attached with running stitches, represented by the dotted lines, and the tear is secured with laid couching. Illustration by Isak Nilsson.
Figure 4. Surrogate with abrasion, conserved with M1. A support fabric is centred under the abraded area and attached with running stitches,represented by the dotted lines, and the damage is secured with laid couching. Illustration by Isak Nilsson.
3.2.4. Securing the Damage in M2
A support fabric was aligned and secured to the surrogate in the same way as in M1 up to securing of the damage.
The damaged area of the surrogate was secured with spaced brick couching. The stitches formed on average 11 rows in the warp direction on the surrogates with c. 5 mm spacing. The stitches on the face side were c. 1 mm long and c. 4 mm long on the reverse. The length of the stitching rows on the surrogates with tear was by turns c. 25 mm and c. 20 mm (Figure 5). For surrogates with abrasion, the length of the stitching rows varied depending on the form of the damage (Figure 6). The amount of needle insertions for the surrogates with tear is c. 300 and for the surrogates with abrasion c. 550 (including the 150 needle insertions for the attachment of the support fabric). This method was carried out on 15 surrogates of each type of damage.
3.2.5. Securing the Damage in M3
The damaged area was covered by crepeline. The edges of a 120 x 120 mm square of silk crepeline were folded to create a 95 x 95 mm square piece of fabric that was centred and aligned over the damaged area. The fabric was attached, close to the edge of the crepeline with c. 1 mm long running stitches on the face side with c. 5 mm spacing giving a total of c. 155 needle insertions (Figures 7 and 8). This method was carried out on 15 surrogates of each type of damage.
Left to right:
Figure 5. Surrogate with tear conserved with M2. A support fabric is centred under the tear and attached with running stitches, represented by the dotted lines, and the tear is secured with spaced brick couching. Illustration by Isak Nilsson.
Figure 6. Surrogate with abrasion, conserved with M2. A support fabric is centred under the abraded area and attached with running stitches, the dotted lines, and the damage is secured with spaced brick couching. Illustration by Isak Nilsson.
Figure 7. Surrogate with tear conserved with M3. The crepeline, illustrated by the darker square, is attached by running stitches, represented by the dotted lines, onto the surrogate. Illustration by Isak Nilsson.
Figure 8. Surrogate with abrasion, conserved with M3. The crepeline, illustrated by the darker square is attached by running stitches, represented by the dotted lines, onto the surrogate. Illustration by Isak Nilsson.
3.2.6. Accelerated Wear
Many historical costumes have a lining, which acts as a protection and support to a costume’s outer fabric. To make the accelerated wear more natural, the surrogates were given a temporary lining of standard silk, ISO 105-F06:2000 Bombyx mori, attached by running stitches close to their edges. The lining protected the reverse of the surrogates and the accelerated wear was concentrated to the face side. The accelerated wear was accomplished by washing the surrogates at 60ºC according to EN ISO 6330:2012 for 30 minutes, thereafter they were tumbled in a tumble dryer, Electrolux T2130, according to EN ISO 6330:2012 (20ºC) with a 2 kg polyester makeweight2 for a period of 660 minutes plus additional 60 min in 50ºC; the makeweight was re-wetted after every 180 minutes. The lining was removed after the accelerated wear was completed.
Normal museum handling is much less severe than this accelerated wear. This treatment was necessary in order to speed up the effect, trying to mimic natural handling over a long period of time. Of the 110 aged surrogates, accelerated wear was carried out on 30 surrogates with tear and 30 with abrasion. Ten of each were conserved with either M1, M2 or M3.
Figure 9 shows surrogates with abrasion before and after accelerated wear: the damage area is larger, the crepeline has become distorted and there is a loss of material which might be considered too great compared to naturally worn textiles. For comparison, however, Figure 10 and 11 show an antependium and a chasuble in silk that have undergone a great deal of handling after the conservation with laid couching (antependium) or brick couching (chasuble). These naturally worn objects, just like the surrogates exposed to accelerated wear, show a severe loss of material supporting the validity of the achieved level of accelerated wear. The antependium’s laid couching is partly damaged while the brick couching on the chasuble is intact.
Left to right:
Figure 9. Details of surrogates with abrasion, before and after accelerated wear: secured with laid couching (A); secured with laid couching after accelerated wear (B); secured with spaced brick couching (C); secured with spaced brick couching after accelerated wear (D); covered with silk crepeline (E); covered with crepeline after accelerated wear (F). Photo: Erik Lernestål.
3.2.7. Tensile Tests
To determine the ageing effect and to ensure that the tenacity was similar to that of 17th century silk, found by Nilsson , weft yarn was tested on a Vibroscope/Vibrodyne device (Lenzing, Germany). Ten weft yarns of a circular surrogate and ten from a rectangular one were tensile tested. The samples were conditioned at 20 ± 2°C and 65 ± 3% RH 24 h prior to testing. The Tex3 value was calculated by taking out ten yarns from the weft of each sample, measuring the average length and weight of the yarns. For the yarn tensile testing the gauge length was 20 mm, the test speed 20 mm/min and the tension weight 2000 mg following DIN EN ISO 5079.
Tensile tests of the fabric surrogates were performed according to EN ISO 13934-2:1999, the grab method. Equipment was an Instron 5966 (Instron, USA). The surrogates’ size follows the testing standard and they were conditioned for 24 h prior to testing in an atmosphere of 20±2 ºC and 65±3% RH. Each surrogate was fastened between clamps, 5 mm from the support fabric and the crepeline (Figure 12), the gauge length being 100 mm and the test speed 50 mm/min. The force was applied in the warp direction of the surrogates, the same direction as the rows of the laid couching and brick couching stitches. The surrogate was extended until it started to rupture, defining the maximum force at break.
Every combination of the two types of damage, the three conservation methods and the four steps of treatment forms a set of conditions. Five unaged specimens and five surrogates of each set of conditions were tensile tested and submitted to statistical tests. For the tests of significance, One-way ANOVA, was performed to ensure that reliable effects were obtained. When the general test was significant, pair-wise differences were analysed using LSD or Tamhane’s T when the two variances were similar or dissimilar, respectively (SPSS Statistics v22).
Left to right:
Figure 10. Detail of an antependium by Agda Österberg 1931, Christiane Church. The conservation with laid couching has become worn by time and the antependium is in need of re-conservation. Photo by Ingeborg Skaar.
Figure 11. Detail of a chasuble by Sten Kauppi 1970, Sunne Church. The stitches from the conservation with brick couching are left and parts of the fragile silk are gone. Photo: Ingeborg Skaar.
Figure 12. Surrogates mounted for tensile test: 1) Insert, 25 mm width, 2) Clamp 50 mm width. Illustration by Isak Nilsson.
4. Time Required to Execute the Interventions
In order to measure the time it took to carry out the conservation interventions, another 24 surrogates (12 of each type of damage) were conserved with Methods 1, 2 or 3 as described above. Four surrogates with the same type of damage were conserved with each method. The conservation was executed by Augusta Persson, employed at the Royal Armoury’s workshop at the time, and the author. Each conservator treated two surrogates with each method and damage. Before conservation, the surrogates were lined with the standard silk ISO 105-F06:2000 Bombyx mori. This step was taken as historical costumes usually have a lining and it is more complicated and time consuming to conserve a fabric that is lined as it is preferable not to stitch into the lining. Therefore, the comparison between the times used to execute the different support methods with a lining will be realistic. Laid couching took on average 68 min to execute while brick couching took 40 min and crepeline 56 min.
5.1. Effect of Ageing, Damaging, Conservation and Accelerated Wear
The yarn in the artificially aged surrogates had on average 17.5% of the tenacity of unaged standard silk. This fragility is close to the Nilsson et al. finding that silk yarn from 17th century costumes had 17% of the tenacity of unaged standard silk .
Before proceeding to the main question, if there are significant differences between the effects of the three conservation methods, the general state of the silk surrogates after each step of the cumulative experimental treatment (conservation, accelerated wear and removal of conservation) will be accounted for in relation to original, aged surrogates (Figures 13 and 14).
The damage by tear or abrasion left only 5% of the relative maximum force at break, and upon conservation the strength was increased four times to 20%. The subsequent accelerated wear left about 9% and when the conservation was removed, 4% remained of the relative maximum force.
5.2. Maximum Force at Break After Conservation
One of the running stitches in the weft direction, which attached the support fabric or the crepeline to the surrogate, was most often first to break during tensile testing of the conserved surrogates. This was followed by breakage of the thread in the laid- or brick couching. Not until a major part of the couching had been disrupted, would the surrogate itself begin to break.
For conserved surrogates with tear, both laid couching and brick couching increased maximum force at break significantly more than crepeline (p= .003 and .026, respectively). The maximum force at break of the conserved surrogates with tear became more than one and a half time stronger with crepeline, three times stronger with brick couching and more than four times stronger with laid couching (Figure 15).
For conserved surrogates with abrasion, laid couching was superior to both brick couching and crepeline (p= .001 and .003, respectively). The maximum force at break for the surrogates with abrasion, conserved with crepeline or brick couching became two and a half time stronger and with laid couching almost four times stronger (Figure 16).
Left to right:
Figures 13 and 14. Relative maximum force at break after each step of experimental treatment for M1, M2, M3 and each damage. For comparison reason the maximum force at break for the aged, undamaged silk is set as the relative value of 100% (which is 17.5% of the strength of unaged standard silk). In Figure 14, the green and red line override each other being thus only visible one line.
Figure 15. The maximum force at break of surrogates with tear without any conservation and after conservation with three different methods, after being subjected to accelerated wear and after removal of the conservation.
Figure 16. The maximum force at break of surrogates with abrasion without any conservation and after conservation with three different methods, after being subjected to accelerated wear and after removal of the conservation.
5.3. Maximum Force at Break After Accelerated Wear
After the conserved surrogates had been subjected to accelerated wear, there were significant differences only for surrogates with tear. Both laid couching and brick couching had significantly higher maximum force at break after accelerated wear than crepeline (p= .003 and .005, respectively). The strength of the surrogates was about halved by the accelerated wear (Figure 15).
When visually inspecting the material loss of the surrogates that have been subjected to accelerated wear, it is impossible to separate the surrogates with abrasion with laid couching and those with brick couching from each other. It is clearly visible though, that the frayed material of the surrogates with abrasion, conserved with crepeline has lost less material than the other two. The crepeline has become ruined by the accelerated wear but seems to have had a function as a protection and a sacrificing layer.
5.4. Maximum Force at Break After Removal of the Conservation
After accelerated wear followed by removal of the conservation, there are significant differences only for surrogates with abrasion. Surrogates treated with laid couching and brick couching were significantly weaker after the conservation had been removed than surrogates conserved with crepeline (p= .015 and .017, respectively). The stitching with laid couching and brick couching decreased more than half the strength of the surrogates while crepeline decreased less (Figure 16).
The artificial ageing method used in this study creates a fabric with fragility similar to examples of 17th century silk from the costume collections of the Swedish Royal Armoury. The results of this study may therefore be applied to silk costumes from that period and to other silk fabrics of similar fragility.
Laid couching and brick couching were sewn with the same number of rows in the study. This similarity is important for the comparison between the methods. As Asai et al.  have demonstrated, the extension of tapestry surrogates may be affected by the number of sewn rows. According to the preliminary data obtained in the present study, extension and maximum force at break show high correlation at supportive conservation. When maximum force at break has a high value, the value for extension is low and vice versa. The importance of sewn rows is also indicated by the observation that the first to break are the running stitches. The reliability of the study can be further supported by the fact that laid couching and brick couching were sewn with almost similar number of stitches, laid couching was sewn with only 7%-9% more stitches; the differences are so small that they probably do not explain the top positions of laid couching.
The relatively great standard errors of mean of the conserved laid couching and brick couching samples should be noted. They tend to obscure reliable differences.
It is evident that conservation, especially with laid couching and brick couching, greatly increases the maximum force at break of damaged surrogates. However, the damaged and conserved surrogates had on average only 20% of the strength of aged surrogates that had not been damaged. In comparison, laid couching had a strengthening effect of 27% on surrogates with tear and 24% on surrogates with abrasion, while the corresponding values for brick couching were 22% / 17% and for crepeline 14% / 18%. Thus, the performed conservation interventions are far from restoring the damaged surrogates to their original strength. This result may be disappointing but it might as well be considered an advantage. If a conserved fragile textile is exposed to stress, the conservation will likely break before the undamaged area of the textile is harmed. This perspective is supported by the observation that the first to break are the running stitches and then the couching before the surrogate itself is visibly affected. The amount of rows of stiches probably affects the strength of the conservation intervention. These are important aspect in decision making concerning what conservation method to choose. This is a topic for further investigation.
Both at intact conservation and after accelerated wear, laid couching gives the strongest surrogates and brick couching is second best. However, there seems to be a slight trend that surrogates with tear as well as with abrasion, conserved with laid couching or crepeline are more negatively affected by accelerated wear than brick couching. The thread is probably more exposed and sensitive to wear with laid couching stitches, as is the crepeline placed on top of the damage; this might cause differences in resistance. After the conservation has been removed, the strength is greater for surrogates conserved with crepeline than those with laid couching or brick couching. This may be explained by the lower amount of needle insertions needed by the crepeline method, but also by the fact that crepeline acts as a protecting layer of the aged and damaged silk. After accelerated wear crepeline has become ruined but seems to have had a function as a protection and sacrificing layer.
Under these simplified conditions, brick couching was the conservation method that required the shortest time to execute, followed by crepeline while laid couching was the most time consuming. However, as type of object, damage and material can vary a lot when working with real textiles, the time for executing the conservation might differ considerably from those registered here. There may also be considerable differences between conservators with different experiences and skill.
This study assessed how three common textile conservation methods affect maximum force at break of silk surrogates with similar fragility as the silk fabric in authentic 17th century costumes. The surrogates were damaged by tear or abrasion and then submitted to three experimental treatments: conservation with one of three stitching methods, accelerated wear, and removal of the conservation. Strength was tested after each treatment. Included in the study is a comparison of how much time each method took to execute.
The three conservation methods were laid couching, brick couching, and conservation with crepeline. After conservation, laid couching made both surrogates with tear and with abrasion the strongest though brick couching made surrogates with tear almost as strong. After accelerated wear, the surrogates with tear and laid couching as well as with brick couching were still stronger than the ones with crepeline. After the conservation was removed, however, crepeline in objects with abrasion gave the strongest surrogates of the methods. Laid couching took the longest time to execute and brick couching the shortest.
It is important that the silk fabric to be conserved is in such conditions that it withstands extensive stitching if laid couching or brick couching is chosen. If a very fragile silk is to be conserved, crepeline is suggested to be the best method as the amount of stitches is low and the crepeline still has a good protective effect for surrogates with both types of damage. In addition, crepeline affects the strength of fragile silk less than the other two methods, as shown after removal of the conservation interventions. A harmless conservation is especially important when conservation may have to be replaced in due time.
Further tests should follow as there are several more combinations of materials, conservation methods, support materials and conservators with different experiences and skills to be investigated. Also, other effects of the conservation interventions such as on extension and modulus are interesting to study. The aesthetical appearance of the conservation is important and should be evaluated. The tentative interpretation of some data in this study that brick couching is less vulnerable to accelerated wear than laid couching or cover with crepeline must be further investigated.
The author is very grateful to the Swedish Royal Armoury and Skokloster Castle and the Hallwyl Museum Foundation, the Department of Conservation from the University of Gothenburg and the following funding bodies: The Gyllenstiernska Krapperup Foundation, The Barbro Osher Pro Suecia Foundation, The Royal Society of Arts and Sciences in Gothenburg and The Sibling Bothéns Foundation. Abegg Foundation is thanked for generously sharing their conservation reports. Prof. emeritus Carl-Otto Jonsson, from the Stockholm University’s Department of Psychology, is thanked for the statistical analysis, and Isak Nilsson, from the School of Engineering Sciences at the Swedish Royal Institute of Technology for the illustrations. Augusta Persson, from the Royal Palaces, is thanked for her conservation work, and Ingeborg Skaar, from Textilvård, is thanked for her photographs. Thanks also go to independent conservator Anna Stow, for checking the language.
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 J. Nilsson, F. Vilaplana, S. Karlsson, J. Bjurman and T. Iversen, The validation of artificial ageing methods for silk textiles using markers for chemical and physical properties of seventeenth-century silk, Studies in Conservation 55(1), 2010, pp. 55-65
 J. Nilsson, A survey of the most common support methods used on historical costumes and a preliminary investigation of tests assessing the quality of conserved fabrics, in: R. Jannaway, P. Wyeth (eds.), Proceedings of the Conference Scientific analysis of ancient and historic textiles: informing preservation, display and interpretation, Southampton, 13-15 July 2004, Archetype, London, 2005, pp. 79-85
 M. Winslow Grimm, The directory of hand stitches used in conservation, The American Institute for Conservation of Historic and Artistic Works, Washington, 2002
 K. Gill, Tapestry as upholstery: the challenges of conserving tapestry-covered seat furniture, in: F. Lennard & M. Hayward (eds.), Tapestry Conservation: Principles and Practice, Butterworth-Heinemann, Oxford, 2006, pp. 113-122
 S. Cussell, Tapestry conservation techniques at Chevalier Conservation, in: F. Lennard & M. Hayward (eds.), Tapestry Conservation: Principles and Practice, Butterworth-Heinemann, Oxford, 2006, pp. 145–152
 M. Harper and K. Thompson, Made to fit: reinstating a set of tapestries and painted panels into the Audley End Tapestry Room, in: F. Lennard & M. Hayward (eds.), Tapestry Conservation: Principles and Practice, Butterworth-Heinemann, Oxford, 2006, pp. 193–199
 J. Nilsson, Stitched support methods using laid couching, brick couching and crepeline attached by running stitches, Youtube, https://www.youtube.com/watch?v=eoogh96C7eI (accessed 21 September 2015)
 M.W. Ballard, Elongation, Hanging Out: Strength and Relative Humidity: Some Physical Properties of Textile Fibers, in: M.M. Brooks, D.D. Eastop (eds.), Changing Views of Textile Conservation, Getty Conservation Institute, Los Angeles, 2011, pp. 189–198
1 The standard EN ISO 12947-2:1999 has the high uncertainty of ± 21% which clearly illustrates the complication of trying to produce uniformly damaged surrogates by abrasion with this method.
2 Makeweight is used to keep the material in an even process and to give the material a certain weight according to the standard.
3 The linear density of thread is a measurement of its fineness and is expressed in Tex units, which is the weight in grams of 1000 m thread.
List of suppliers
Standard silk ISO 105-F06:2000 Bombyx mori from Cromocol, Åsboholmsgatan 16, SE-504 51 Borås, Sweden.
“Hair fine silk”, originally weaving yarn imported from France. Silke-Annet, Dorthesvej 2, Dk-3520 Farum, Denmark.
Silk crepeline. Talas, 330 Morgan Ave, Brooklyn, NY 11211, US.
Glass bottles from se.vwr.com art. no 215-1595.
Calcium chloride 99% purity from Sigma Aldrich USA.
The Royal Armoury and Skokloster Castle with the Hallwyl Museum Foundation
Fil. lic. Johanna Nilsson is since 1990 textile conservator at the Collection Department at the Royal Armoury and Skokloster Castle with the Hallwyl Museum Foundation, Stockholm. Since 2010 she is conducting PhD studies at the Department of Conservation, University of Gothenburg.