Introduction

All objects such as manuscripts, paintings, ornaments, clothes, carpets, and rugs possessed by a civilization are reflections of the formation of that civilization. All of these objects embody ideas and values and are cultural elements that contain much more than representations [1].

Since ancient times, organic coloring materials have been attractive to human beings, and have obtained these materials by using living things in nature such as plants, insects, and lichens [2, 3]. Natural dyes and colorants are an important part of cultural heritage and throughout history, these natural materials have played an important role in economic and cultural exchanges between countries [2, 4].

The dyes used and the dyeing industry by the Ottomans were handed down from father to son as a secret for generations and reached us almost without any significant change. Due to the careful production process in the Ottoman Empire, dyestuffs were of great commercial importance. Some natural dye resources and dyed textiles were used to pay taxes in the Ottoman Empire, and dye workshops paid some of their production or harvest to the state in this way instead of cash. In general, it is understood from the Ottoman archives that the Ottoman Empire was rich in the production of dye sources and dyed textiles in the sixteenth and seventeenth centuries [5].

The use of natural dyes in textiles continued until the second half of the nineteenth century. The discovery of the first synthetic organic dye (mauveine) by William Henry Perkin in 1856 and its subsequent introduction to the market created a major breakthrough in the dye industry. In addition, synthetic dyes have replaced natural dyes due to their cheapness and easier application on the textile surface, and this result has led to a cultural revolution [4]. With the spread of synthetic dyes, these dyes entered the Ottoman market, and dyehouses started to close one by one [6].

Metallic threads in textiles, especially those wrapped using gold and silver, have been used throughout history both to adorn textile products and as a visible proof of magnificence, power, abundance, and wealth [7]. Early textiles decorated with different metallic threads have often been among the most valuable and admired historical objects in museum collections. At the end of the nineteenth century, with the spread of cheaper synthetic threads, the use of metallic threads in weaving, embroidery, and other decorations (tassel, lace, etc.) became widespread, and accordingly, the value of textiles with metallic threads decreased [8].

The main elements in wire and metallic threads used to decorate textile objects are gold, silver [9,10,11], and copper. Each element can be used alone or together [10,11,12]. That is, gold-like copper alloys such as gold alloyed with silver, silver coated with gold, copper, or brass coated with silver have been used in the production of metallic threads [10]. The most commonly used material to imitate gold is brass [8]. Since the beginning of the twentieth century, some new materials such as synthetic yarn and aluminum have also been used in making metallic thread [11, 12].

In this study, an examination was made on the palace weavings with metallic thread found in TPM. For this purpose, a total of 7 metal threads palace weavings, the earliest of which is dated to the sixteenth century and the latest to the end of the 19th/beginning of the twentieth century, have served various purposes were selected. By using non-destructive (color measurement and OM) and micro-destructive (HPLC–PDA and SEM–EDX) analytical methods and techniques, material characterization, production technology, and deterioration/corrosion products due to various factors were determined.

Within the scope of the analysis, color measurement was carried out using the CIEL*a*b* spectrophotometer from the colored areas in each textile object. An OM was used for documentation and determination of technical characteristics such as fiber type, weaving technique, yarn twist direction, and warp/weft density. Many studies on historical textiles using OM have been reported [13,14,15,16,17] and in these studies the determination of fiber type, various technical analyses such as the determination of the twist direction of wire, strip, and core fiber, detection of surface wear and corrosion, and defining the color of core fiber in metal threads.

Analytical identification of dyestuffs in order to preserve cultural heritage and convey it to future generations is extremely important in terms of obtaining information about which dyes were used in the past, habits, and social status of textile owners, trade-in artifacts, and dyeing technology. In addition, for conservators, having detailed information about dyes enables them to choose suitable materials and methods for conservation studies [18]. The biggest reason for this is related to the conditions in which textile works can be exhibited in a museum environment. In their study, Padfield and Landi performed a light fastness test on wool samples dyed with natural dyes to understand the reaction of dyestuffs to light, and they reached sufficient information on wool fiber at that time [19]. Knowing these facts helps the curator and conservator to make decisions regarding the safety of exhibition lighting, storage conditions, and preservation processes [20]. In this study, HPLC–PDA was used for the detection of dyestuffs. HPLC is the most preferred method for the detection of dyestuffs and the natural dye sources used. Many studies have been reported in the literature on this subject [14,15,16, 21,22,23,24,25,26,27,28]. With the technology developed in HPLC, analysis can be performed much faster and in a short time, and the name of this new technology is ultra-high performance liquid chromatography (UHPLC). Li et al. and Serrano et al. are some of the researchers working with UHPLC on dyes in historical textiles [29,30,31]. Serrano et al. conducted a study on 66 historical samples and 141 dyed wools using the UHPLC method [31]. Another innovation in HPLC is seen in the mass spectrometer working with it. Most researchers [32,33,34,35,36,37,38,39,40,41] were able to identify small amounts of dyes that were difficult to identify with HPLC–DAD using HPLC–MS or HPLC-MSn methods.

Scanning electron microscopy-energy dispersion X-ray spectrometry (SEM–EDX/EDS) is an analytical method frequently used to determine the elemental composition in metallic threads found in textile artifacts [8, 25, 26, 42, 43]. Many studies have been reported in the literature on this subject [13,14,15, 17, 25, 26, 43,44,45,46,47,48,49]. It is described as a non-destructive technique, even though there is no detectable electron beam damage [50].

Ottoman weavings

Turkish fabrics have an important place in world fabric production in terms of material and pattern richness [51]. Ottoman weavings are fabrics with earmark character and style, which started with the Great Seljuks and then became richer with the Anatolian Seljuks [52,53,54]. The fact that the Ottoman Empire was a bridge between the East and the West not only developed commercial exchanges but also developed the interaction of culture and art [55].

The ornaments, richness, and splendor of weaving are striking in the weaving samples, miniatures, and written documents that have survived to the present day. The weavings used by the sultan, her harem and rulers in all areas are examined under the name of “palace weavings”. The materials used in these weavings were mostly silk, gold, silver, and precious stones such as pearls [56].

The woven fabrics (upholstery, curtains, bundles, etc.) that are specially woven for the sultan and the courtiers and meet the needs of the palace, not only as clothes, are called palace fabrics [51, 56]. These fabrics were obtained through orders, gifts, war spoils, and purchases [51]. The sultan wore caftans called “seraser” in big ceremonies attended by the public, but since these caftans were stiff, they preferred kemha (silk brocade), velvet, or plain fabrics on less formal occasions [57].

As a tradition, Ottoman palace clothes and fabrics were kept in bundles until the last period of the Ottoman Empire and managed to reach the present day. Thanks to the labels on each bundle, it is known to which palace member the clothes such as caftan and dress belong [51, 52, 57, 58]. One of these clothes, which belonged to the sultan or a member of the dynasty, was put in her tomb after she died [57].

Red color has been dominant in Turkish fabrics [52, 55, 59]. The second rank is blue [55]. Other frequently used colors are green, white, beige, golden yellow [52, 59] and purple. It is known that the Turks developed and produced many color tones apart from these basic colors. The fact that Anatolia has a wide variety of plants has also facilitated the acquisition of new colors in the art of dyeing [59]. Colors and tones vary according to the periods. Two-colored fabrics were woven before, and it was seen that seven-colored fabrics began to be woven in Bursa in the fifteenth century [52]. Color harmony in Turkish weavings was not achieved by using the same color tones, on the contrary, it was achieved by bringing opposite colors side by side [55].

Although examples of woven fabrics were seen in the fourteenth and fifteenth centuries at the earliest, the sixteenth century is very important for Ottoman weaving, and Turkish cloth-making reached its peak in this century. In this century, Turkish silk fabric weaving became unrivaled and silk fabrics were sold to most countries of the world [60]. Turkish weaving experienced its heyday in the sixteenth century, but the deteriorating economic situation towards the end of this century also affected weaving [55]. There was a pause in the seventeenth century and a decline in the Ottoman fabric industry towards the end of this century [54, 61]. From the tailor's notebooks found in Topkapı Palace, it is understood from the orders that plain and modest fabrics increased gradually in the seventeenth century. In the seventeenth century, there was a decline in the production of fabrics with gold and silver, which caused changes in colors and motifs. The decline seen towards the end of this century continued in the eighteenth century [61]. Sultan Ahmed III (1703–1730) banned the use of silver wire in fabrics in order to reduce the consumption of silver. When the quality of Turkish fabrics began to deteriorate, fabrics from Europe entered the market and the quality of old fabrics was gradually forgotten [52]. The decrease in material quality in the nineteenth century also affected the quality of the fabric produced. Although various fabric factories were established within the borders of the empire in the nineteenth and twentieth centuries, the old quality and splendor were not seen in fabrics [54, 61].

Silk weaving in the Ottomans was carried out in a guild system called “hirfet” and there were people belonging to different duties in this system. The first of these is those who meet the raw material needs, the second is the weavers and the third is the investors who market the product. Apart from this, “hamcılar” who buy raw silk and produce weft and warp yarn, loom manufacturers, “simkeş” who makes gold and silver metallic yarn/wire, and dyers have formed the sub-industry branch that provides materials to weavers [57].

TPM and its textile collection

After Istanbul was conquered in 1453, the construction of Topkapı Palace was started in 1460 at the request of Fatih Sultan Mehmed (Mehmed II), it was completed in 1478 and continued to expand with the structures added to its structure until the nineteenth century. Topkapi Palace, which was built on an area of 700.000 m2 on the East Roman Acropolis in Sarayburnu, was the residence of the Sultans for about 400 years, as well as the administrative, educational, and artistic center of the Ottoman Empire. Topkapi Palace, which was turned into a museum on April 3, 1924, after the foundation of the Republic of Türkiye, has the distinction of being the first museum of the Republic. In addition, it is one of the largest palace museums in the world with its architecture and unique collections [62].

It is known that the tradition of bundling, which started with Fatih Sultan Mehmed in the Ottoman Empire, continued until the beginning of the twentieth century, and the majority of the textile objects that were saved during this period are now preserved in the TPM. There are approximately 2500 historical textiles in this collection, and most of these objects consist of velvet, silk brocades (Turkish names are kemha, and seraser) weaving caftans and shalwars. It has been observed that the fabric types of the caftans in the collection have changed over time, but their forms have remained the same [51].

Experimental

Historical textiles

In this study, a total of 7 metal thread palace weavings, dated to the 16th-19th/beginning of the twentieth centuries, which contain the most unique examples of Ottoman palace weavings and are included in the textile collection of TPM, were examined and researched. The visuals of the examined historical textiles are presented in Fig. 1 (except Inv. No. 13/1060), general information about them and the number of samples taken for analysis are shown in Table 1.

Fig. 1
figure 1

The historical textiles examined from Ottoman palace weavings belonging to different periods

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Table 1 Characteristics of the examined historical textiles
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Some OM images of the historical objects examined for this study, color measurements, taking samples for dyestuff and elemental analysis, and pictures of the historical textiles are within the scope of the “Project of Restoration and Conservation of the Sultan Clothes in the Topkapi Palace Museum” performed [63, 64]. Colored and metallic thread samples from historical textiles were carefully taken from the damaged areas and the inner parts of the object.

Chemicals and dyestuff standards

The reference dyestuff standards and chemicals were provided by Turkish Cultural Foundation-Cultural Heritage Preservation and Natural Dyes Laboratory (TCF-DATU) in Istanbul, Turkey. Acetonitrile, trifluoroacetic acid (TFA), methanol, and dimethylformamide (DMF) were purchased from Merck (Germany), also dimethyl sulfoxide (DMSO) was obtained from Sigma Aldrich (the USA). All chemicals employed in this investigation were of analytical grade and were used as received unless stated otherwise. High-purity water was obtained by passing water through a Milli-Q treatment system (Millipore, Bedford, MA, the USA), and the HPLC mobile phase was prepared using Milli-Q water. A standard gradient elution program was used for chromatographic separation by HPLC–DAD [15, 26, 65,66,67,68].

The following dyestuff standards were obtained from commercial sources and used as references: ellagic acid from Alpha Aesar (the USA), luteolin from Roth (Germany), and indigotin, indirubin, carminic acid, apigenin, alizarin, and purpurin from Sigma Aldrich (the USA). Flavokermesic acid, xhantopurpurin, and sulphuretin were obtained from the analysis of plant and insect extracts. Details on the retention time and UV–Vis data belonging to these dyestuff standards are shown in Table 2.

Table 2 The retention times and the UV–Vis spectra (absorbance maxima) at HPLC–PDA of reference dyestuff standards
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Color measurement

Konica Minolta branded CM-2300d model, a CIEL*a*b* spectrophotometer (6500 °K) with Spectra Magic NX software was used for the numerical value of the colors that can be measured in the textile objects examined.

OM

Thanks to OM, images of different magnifications (max. X90) from historical textiles were taken, contributing to the documentation work. In addition, it was determined that the type of weave, weft-warp density, and yarn twist directions. A polarized OM with model SZ2-ILST from Olympus SZ61 was used for this study.

HPLC–PDA

Sample preparation

All colored samples were weighed (0.5–1.2 mg) before HPLC analysis. Later, all samples were hydrolyzed in 400 mL of a solution mixture of 37% HCl:MeOH:H2O (2:1:1, v/v/v) in conical glass tubes for exactly 8 min in a water bath at 100 °C to extract organic dyestuffs. After rapid cooling under cold running water, the solution was evaporated just to dryness in a water bath at 60–65 °C under a gentle stream of nitrogen. The dry residues were then dissolved in 400 mL of MeOH:H2O (2:1, v/v). For the green samples, solubilization was also applied by passing 400 mL of DMF or DMSO over the remaining colored residue. Then, the samples were centrifuged at 4000 rpm for 10 min. After centrifugation, the upper clear part was taken into vials. 100 µL of the supernatant from each sample was analyzed in the HPLC [25, 26, 69, 70].

Instrumentation

Chromatographic separations were carried out using an Agilent 1200 series system (Agilent Technologies, Hewlett-Packard, Germany) including G1322A Degasser, G1311A Quat pump, G1329A autosampler, G13166 TCC, and G1315D Diode Array Detector. PDA detection was performed by scanning from 191 to 799 nm with a resolution of 2 nm, and the chromatographic peaks were monitored at 255, 268, 276, 350, 491, 520, 580, and 620 nm. A Nova Pak C18 analytical column (39 × 150 mm, 4 μm, Part No WAT 086344, Waters) was used. An analytical column protected by a guard column filled with the same material was used. Analytical and guard columns were maintained at 30 °C and the data station was the Agilent Chemstation. Two solvents were utilized for chromatographic separations of the hydrolyzed historical samples. Solvent A: H2O-0.1% TFA and solvent B: CH3CN-0.1% TFA.

SEM–EDX

Sample preparation

The analyses were performed by SEM–EDX at energy levels of 5, 10, 20, and 30 keV and under a high vacuum. Since it will be worked under a high vacuum, metallic thread samples were fixed on the sample holder by being attached to a carbon band that did not affect the analysis result. Since the morphology and elemental analyzes of the metal strips in the samples were carried out, no coating process was applied. SEM images were obtained using BSE and SE detectors.

Instrumentation

A SEM with a VEGA3 model of TESCAN brand (TESCAN, Brno, Czech Republic) equipped with a backscattered electron (BSE) detector, secondary electron (SE) detector, and EDX was used for this study. Also, a thermionic emission tungsten heated filament was used as the electron source, and a Bruker brand XFlash 410-M model EDX detector (ESPRIT Compact Esprit 1.9 software) was used for elemental analysis. Thanks to the EDX detector, semi-quantitative results were obtained as atomic and percent by weight. Qualitative microanalysis was carried out using the ZAF method, which allows the simultaneous determination of the concentration of each element in a multi-element material and is based on the correction of the matrix effect. This method provides X-ray intensity correction, absorption correction, and fluorescence correction produced by the composition and depth of electron penetration, and the atomic number effect of each element by secondary fluorescence, respectively.

Results and discussion

Visual assessment for documentation

The first step in the analysis of archaeological and historical objects is a visual and photographic examination. This approach is particularly useful when working with colored objects and samples [3]. In this study, firstly, a naked-eye examination was made both to assist the documentation studies and determine the current status of the historical objects. In addition, some images were obtained with a camera and a three-dimensional scanner. Accordingly, the deteriorations detected in the examined historical textile objects are as follows.

  • When the general condition of the object with Inv. No. 13/218 is examined, and it is observed that it is good. It was determined that discoloration of the leather formed the ground of the textile, discoloration of some silk brocade fabric pieces (especially in the silk brocades with blue and dark blue grounds), embrittlement in fiber strength, and fiber abrasions. In addition, it has been determined that there is corrosion and breaks in metallic threads.

  • When the general condition of the object with Inv. No. 13/1455 is examined, and it is observed that it is not good. It was determined that there were abrasions on the ground of red-colored silk, and some fibers and metallic threads were lost by breaking off. It has been determined that the integrity of the pattern is deteriorated due to color breakage in the areas with fiber abrasions. It was observed that the ground's dark red color faded and also corrosion occurred on the metallic threads. In general, it is evident that deformation occurs in the historical textile.

  • It has been observed that the condition of the historical textile with Inv. No. 13/584 is good. There are no two rows of ornamental front closing threads (When looking at the front of the object, although there are 24 rows of front closing thread on the left side, there are 22 rows of front closing thread on the right). The locations of the missing front closing threads on the right are obvious. One is the top first row, and the other is the 7th from the top (with the missing front closure string in the first row). In addition, it was determined that one of the cylindrical buttons at the end of the front closing threads was missing (at the top), and there were losses in the white metallic threads wrapped around the other existing buttons. It has been observed that the colors on the back of the object are more high-colored than the front, and this is probably due to the exposure of the front face to inappropriate light and lighting during the exhibition. Apart from these, it was detected that fold lines, and corrosion on the metallic threads.

  • When the general condition of the object with Inv. No. 13/929 is examined, and it is observed that it is good. Abrasions and thread breaks were observed in the metallic threads in the wide part of the object. It is thought that this is probably related to the use in the period. At the same time, insect holes in the fabric surrounding the light green inner edge and staining due to insect droppings were observed around these holes. In addition, it was determined that the metallic thread was corroded.

  • When the general condition of the object with Inv. No. 13/1893 is examined, and it is observed that there are different types of deterioration in the historical textile. According to this, discoloration of the fabric surrounding the ground and inner edge, intense thread breaks and thread losses in the pattern with white metallic thread, breaks in yellow metallic thread, corrosion in all metallic threads, embrittlement in fiber strength, and abrasion in ground yarns, fold line, loss of parts in the orange silk fabric in the waist area, and staining on the cotton lining fabric were observed.

  • It has been observed that the condition of the objects with Inv. Nos. 13/816 and 13/1060 is good. Only, corrosion has been detected on metallic threads and metal wires.

Color measurement

The colors in each textile object were measured using a CIEL*a*b* spectrophotometer in the fabric storage where the historical textiles are located. Color measurement is necessary for contributing to possible restoration studies for the textile objects rather than a comparison between periods. In determining the modern fabric and/or yarn colors to be used in restoration works, there is a need for the numerical value of the existing colors in the historical textile. For this, first of all, it becomes a necessity to measure the existing colors in the historical textile and then the dyed modern materials that will be used in restoration works. The ΔE value is used for the difference between the dyed material to be used in the restoration and the existing color in the historical textile. If the ΔE value is below 1, there is an invisible difference, and if it is in the 1–2 range, there is a slight color difference with a very close observation [71]. In this study, the numerical values of the measured colors are shown in Table 3.

Table 3 Color values of the examined historical textiles
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Technical analysis by OM

Thanks to the non-destructive analytical examinations carried out on the historical textiles using OM, the technical properties of the textile objects such as the type of weave and the warp-weft density can be determined. For this research, in-situ investigations with OM are necessary for determining whether the quality of the weavings has changed between periods and using which types of weaves. This is important in determining the twist directions of the fabric or yarn to be used as a support fabric in restoration work and the weaving type of the fabric to be used. In addition, it is important to determine the technical features and to use appropriate materials in the restoration work so that the restoration area is not understood by a foreign eye and the restored textile object is seen as a whole.

In this study, some images obtained with OM are shown in Fig. 2. In addition, measurements were made with the help of the images obtained with OM, and thus the warp-weft density, which determines the quality of the weaving, could be determined. The results of the fabric type (main fabric and, if any, surrounding in the edge fabric, and lining fabrics) and warp-weft density of the examined textile objects are given in Table 4.

Fig. 2
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Some OM images of the textile objects. (all images X10 magnification for Inv. Nos. 13/218, 13/1455, and 13/816; X10 and X30 magnification from left to right for Inv. Nos. 13/584 and 13/1060; X30, X45, and X30 magnification from left to right for Inv. No. 13/929; X30 magnification for all images for Inv. No. 13/1893)

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Table 4 Results of technical properties of palace fabrics
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In addition to these images, the images of metallic threads samples taken from the historical textiles were obtained using OM (Fig. 3).

Fig. 3
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OM images of metallic thread and wire samples taken from historical textiles. (A Inv. No. 13/218, X40; B Inv. No. 13/1455, X90; C Inv. No. 13/584, X40; D Inv. No. 13/1893 from white metallic thread, X50; E Inv. No. 13/816 metallic thread, X63; F Inv. No. 13/816 metal wire, X50; G Inv. No. 13 /1060, X70)

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Dyestuff analysis by HPLC–PDA

Dye identification for historical and archaeological textiles is usually based on comparison with known reference materials based on the qualitative and quantitative composition of the main colorant components [3, 41]. The analysis of textile dyes by HPLC determines which chemical class or dyeing group they belong to, by identifying the compounds. In addition, qualitative and quantitative information about compounds detected in a chromatogram help identify the dyestuff source. Absorbance detection has a wide range of uses in the identification of dyes, and these compounds respond well to the UV–Vis region of the electromagnetic radiation spectrum [72].

In this study, a total of 15 colored fiber samples from 7 metallic threads palace weavings belonging to different periods were analyzed by HPLC–PDA. The chromatograms obtained according to the analysis results are shown in Fig. 4, and also the detected spectra are shown in Fig. 5.. Since no spectrum could be determined in the yellow color sample in the historical textile with Inv. No. 13/584, the chromatogram was not shown.

Fig. 4
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Chromatograms belong to colored yarn samples. (A brown, B blue for Inv. No. 13/218; C ground red, D blue for Inv. No. 13/1455; E ground red, F light green, G light green-inner edge trim for Inv. No. 13/929; H ground orange, I yellow for Inv. No. 13/1893; J light blue, K purple, L purple with DMF, M light green, N pink for Inv. No. 816; O blue for Inv. No. 1060)

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Fig. 5
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Dyestuff spectra detected in the samples. (EA ellagic acid, IND indigotin, INR indirubin, CA carminic acid, dcII dye component II, dcIV dye component IV, FKA flavokermesic acid, LU luteolin, AP apigenin, AL alizarin, PU purpurin, XHP xhantopurpurin, SU sulphuretin, SDS synthetic dyestuff spectrum)

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The dye sources used were determined according to the detected dyestuff spectra. A summary of all results is shown in Table 5.

Table 5 Dyestuff analysis results of the analyzed samples and possible dye sources
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Red, orange, pink, and purple dyes

The dyestuffs used to obtain the red color and shades in dyeing are divided into two groups as plant and animal origin [2]. The main color obtained from insects is red and the dyestuffs it contains are anthraquinone structure. Dyeing performed with natural sources with anthraquinone structure is highly resistant to photo-oxidative reactions (reactions caused by light) [3]. According to Table 5, it was determined that natural dyes of insect origin were used in a total of 4 samples, red (× 2), pink, and purple.

Carminic acid dyestuff is the main dyestuff of Mexican cochineal (Dactylopius coccus Costa), Armenian cochineal (Porphyrophora hameli Brandt), and Polish cochineal (Porphyrophora polonica L.) insects [2, 3, 73, 74]. The color of one of these samples analyzed is purple, and the Ottomans generally used insect-based dyes together with indigo for the purple color [15, 25, 26, 75, 76]. Additionally, carminic acid derivative dyestuffs such as dc? and dcIV were detected in some samples (Table 5).

The most widely used plant in dyeing in Anatolia is the madder plant (Rubia tincrorum L.) [79]. The dyestuffs (color components) in Rubia tinctorum L. are anthraquinones, which are hydrolysis products of the main dye component, rubierythrin acid. The main coloring components from these anthraquinones are alizarin and purpurin. Other anthraquinones are pseudopurpurin, rubiadin, munjistin, xanthopurpurin, and other small-scale anthraquinone structures [80]. In the 1700s, the Ottoman Empire met two-thirds of the world's need for madder. It is known from the records that the income obtained from the sale of madder, which was made only from the Izmir port in 1875, exceeded 500.000 gold. Until the middle of the nineteenth century, the madder plant took third place in the foreign trade of the Ottoman Empire after silk and grain. However, this situation decreased after 1882 with the spread of synthetic dyes [59]. According to Table 5, alizarin, purpurin, and xanthopurpurin were detected in only one sample with orange color (Inv. No. 13/1893). These data are also compatible with the dyestuff analyses previously performed on Ottoman textiles [76]. This result shows that the roots of the madder plant are used to obtain the orange color. However, since the color is orange, either the first or second water of the dye bath was used, or this color tone was obtained by changing the factors such as pH, temperature, plant ratio, mordant, etc. according to the dyeing conditions.

Yellow and green dyes

Organic natural dyes that give yellow color are obtained from plants and constitute the largest dye group. The primary source of yellow dyes are plants that contain coloring agents belonging to the chemical class called flavonoids [2]. According to Table 5, dyestuff in flavonoid structure was detected in 3 samples. Luteolin and apigenin dyestuffs were detected in both green samples taken from fabrics used in different areas (pattern, and surrounding in the inner edge) in the historical textile with Inv No 13/929. The presence of these dyestuffs shows that one of the most commonly used weld (Reseda luteola L.) and sawwort (Serratula tinctoria L.) plants is used in dyeing [37]. However, it is highly probable that the weld plant, which grows in Anatolia and is known to be used frequently by the Ottomans in yellow and green dyeing, was used [76, 79].

In the analysis of green color in historical textile with Inv. No. 816, only indigotin dyestuff was detected, but yellow dyestuff components could not be determined. Also, no color component was detected in the analysis in yellow sample of the historical textile with Inv. No. 584.

When Table 5 is examined, only in one sample (Inv. No. 1893-yellow) determined the sulfuretin. Sulfuretin dyestuff is found in young fustic plant (Cotinus coggygria L.). The yellow color obtained from the young fustic has been known since the Roman Empire period and is said to have been used in leather dyeing in ancient times, according to Roman Pilinus (23–79 AD). In the nineteenth century, this plant was frequently used to dye silk fiber yellow in Europe and to obtain yellow yarn in carpets in Anatolia [79]. It has also been reported that this plant was used to dye in yellow some Ottoman silk fabrics [25, 81, 82].

Blue dyes

Blue dyes are divided into two animal and plant dyes depending on the sources obtained. But the most widely used is indigo, which is obtained from plants. The main dye sources of indigo are Indian indigo (Indigofera tinctoria L.) and woad (Isatis tinctoria L.) plants [83]. Although natural indigo has different dyestuffs, all of them produce indoxyl, and these dyestuffs can be converted into each other. Indoxyl dyes are indican, indigotin, isatin, indirubin, and other minor indigoid dyes (isoindirubin-red color and isoindigo-brown). In the dyestuff analysis of textiles dyed with natural indigo, indigotin, and indirubin dyestuffs are mostly detected, while it is very difficult to determine which plant source it belongs to [2]. In this study, indigotin was detected in a total of 6 samples, blue (× 3), green (× 2) and purple (Table 5). At the same time, indirubin dyestuff was also detected in the blue sample in the historical textile with Inv. No. 13/218. The blue color component could not be determined in the pattern green sample of historical textile Inv. No. 13/929.

These results show that in addition to the color blue in Ottoman weavings, they used indigo, a color component, to obtain green and purple colors. This result is similar to other studies reported on Ottoman textiles [15, 25, 26, 76, 77].

Tannin

Tannins are very common in the plant world and have been used to obtain beige, brown, gray, and black colors in various cultures since prehistoric times [2]. Tannins are polyphenols that are divided into two main categories hydrolyzable (gallotannins) and proanthocyanidins and have many common properties [2, 3]. Throughout history, gallotannes have been frequently used in tanning leather, in black inks in manuscripts, in weighting silk, as a mordant in the dyeing of Turkey red of cotton, and for dyeing textiles made of various fibers [3]. In this study, ellagic acid, one of the tannin group dyestuffs, was detected in a total of 3 samples (Table 5). It is thought that it was used as the main dyestuff in the brown sample of the historical textile with Inv. No. 13/218, and also in red and blue colors of the historical textile with Inv. No. 13/1455, as a secondary dye or for the purpose the weighting of the silk.

Synthetic dyes

In this study, the historical textile with Inv. No. 13/1060 is dated as the second half of the nineteenth century or the beginning of the twentieth century. Synthetic dyestuff (Fig. 5, Table 5), was detected in the analysis of the blue color taken from this object, and it was determined that this synthetic dyestuff is one of the alkali blue 4B dyestuffs [84].

It is seen that all of the natural organic dyestuffs detected as a result of the dyestuff analysis (except the synthetic alkali blue 4B) were also found to comply with the newly established natural organic dye standard (NODS) standards [85].

Elemental and morphological analyses by SEM–EDX

In this study, metallic thread and wire samples were studied in more detail by SEM microscope after preliminary examination with the help of OM. From the images obtained by SEM microscope, the production method of the metal strip (cutting, rolling, etc.), the presence of physical deterioration, the type of the core fiber, and the corrosion products (such as characteristic Ag2S compound) were determined. In addition, the SEM microscope was used to determine the technical properties of the metal strip. In this study, Technical properties such as the winding width of the metal strip after it is wound on the core yarn, the measurement of the strip width, and the measurement of the thickness of the produced metallic material were determined with the help of an SEM microscope. Some SEM images of a total of 8 samples analyzed for this purpose are shown in Fig. 6.

Fig. 6
figure 6figure 6

SEM images of the metallic thread and wire samples

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According to Fig. 6, it was determined that the metal strip in the metallic thread samples of the historical textiles with Inv. Nos. 13/218, 13/584, and 13/816 were physically deformed. In addition, it was determined that corrosion occurred on the surface of the metal strip in all samples. When the core fiber type in metallic threads is examined, except for one sample (Inv. No. 13/1060), all of them were silk, and it was determined that the sample in the historical textile with Inv. No. 13/1060 was cotton. In addition, it was determined that the metal strip in the metallic threads and the wire sample were produced by first drawing and then rolling. As proof of this, the edges of all metal strips are rounded, and smooth. The technical specifications determined by the SEM microscope are shown in Table 6. These results are similar to the analysis results previously reported on metal threads in Ottoman textiles [15, 25, 26, 76,77,78].

Table 6 Technical specifications of the metallic thread and wire samples
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In this study, surface EDX analysis was performed to determine the chemical structure of metal strips found in metallic thread and wire samples and to detect corrosion products formed on the surface. In addition, elemental analyses were carried out at different energy levels (5 kV, 10 kV, 20 kV, 30 kV) to determine the chemical production method (gilded, alloy, etc.) of the metal strip. The analysis results obtained are presented in Table 7.

Table 7 Elemental analysis results of metal strips
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According to Table 7, the main elements in the yellow metallic thread and wire samples are Au and Ag (except Inv. No. 13/1060). The study was carried out with increasing voltage values and the chemical production method of each sample was determined. Accordingly, it was determined that 5 of 6 yellow samples [Inv. Nos. 13/1455, 13/584, 13/1893, 13/816 (× 2)] were produced by Au gilded on Ag. In addition, as the voltage value increased, the percentage of the Au element decreased, while the percentage of the Ag element increased. As a production method, amalgam was formed with Au element Hg and gilded by heating. However, no trace of Hg element was found in the analysis. Considering that the most recent historical textile was from about 100–120 years ago, it would not be wrong to comment that even the remaining mercury evaporated over time and completely disappeared according to the environmental conditions.

The gilded of silver wires is usually performed in the form of interdiffusion bonding. In this way, gold leaf is coated on the hot sub-layer. The mutual diffusion of gold and silver elements results in a strong metallurgical bond between the two metals. Diffusion bonding is rarely used in copper alloys, as surface oxidation inhibits efficient bonding when copper is heated outdoors [86].

Looking at the results in Table 7, Cu element was detected in all samples. However, except for one sample (Inv. No. 13/816 YS), the copper content in all other samples is very low, so it is highly likely that the copper is an impurity.

Although the color of the core fiber of the metallic thread sample belonging to Inv. No. 13/1060 historical textile was yellow, no Au element was detected in the elemental analysis of the metal strip (Table 7). As it is known, if Au is used in strips or wires in metallic threads, the color of the core fiber is also dyed yellow in order to make this fiber more prominent. However, this was not the case in this sample. It is understood from this that the perception that Au is used in the metal strip is intended to be given by using yellow core fiber. It is thought that this effect is created because the winding density of the metal strip is also not frequent (Fig. 3G).

They determined the chemical composition of the metal strips as well as the corrosion products formed on the surface. In this study, the elements detected as pollution/corrosion, especially in the results obtained from the 5 kV energy level, are C, O, Mg, Al, Si, S, and Cl. The presence of S and Cl elements shows the formation of Ag2S and AgCl products typical of the element Ag. When the S and Cl values were examined, it was determined that the percentage ratios decreased as the voltage value increased and one went deeper from the surface (Table 7).

The most common corrosion product of silver is silver sulfide (Ag2S), also known as argentite or acanthite. This brown-gray mineral is generally passive and this means that it does not readily support further corrosion reactions that can cause metal loss. Therefore, it is considered a protective layer, and usually, the greatest damage it causes is visual [87]. All possible corrosion products (oxides, chlorides, sulfides) are formed on silver surfaces, and the metallic threads found in most historical textiles appear tarnished by oxidation [9]. In this study, the findings obtained from the metal thread and wire samples taken from historical textiles and performed EDX analysis are related to the results of the analysis previously similarly conducted on Ottoman textiles [15, 25, 26, 76,77,78].

There are many air pollutants that can have adverse effects on historical objects in a closed environment. These pollutants can originate from the indoor or outdoor environment. The pollutants found and produced indoors are carbonyl compounds, alternatively called organic acids. The most common pollutants are acetic acid (CH3COOH), formic acid (CH2O2), and formaldehyde (CH2O). The pollutants that can have both internal and external sources are carbonyl sulfide (CS) and hydrogen sulfide (H2S). Substances such as nitrogen oxides (NOx), sulfur dioxide (SO2), and ozone (O3) are generally outdoor pollutants [88]. At the same time, since some cultural institutions such as TPM are located in towns or cities close to the sea, salt pollution occurs on the objects when O3, NO2, SO2, H2S, H2SO4 and HNO3 vapors (typical outdoor pollutants) enter the museum building, which leads to some deterioration (especially corrosion on metals) causes [89]. After these gases are adsorbed on fiber surfaces, they cause chemical reactions that affect fiber properties and cause deterioration [90, 91]. When sulfur and nitrogen compounds combine with moisture and other pollutants in the air, they form H2SO4 and HNO3. That is, they form acid in the presence of moisture, making the textile object acidic and ultimately embrittlement the material. Sometimes they change or fade dye colors [91].

Historical textiles containing metallic threads are adversely affected by indoor environmental pollutants as well as being exposed to inappropriate outdoor pollutants. In particular, attention should be not to keeping textile objects together with wool, felt, and rubber-based materials found in display and storage materials found in any area such as a showcase. Storing and displaying textiles and clothes containing metallic threads in the same area as wool fiber textiles should be avoided [92].

Conclusion

In this study, various analysis was carried out on a total of 7 metallic thread palace weavings, the earliest of which was dated to the end of the sixteenth century, the latest the end of the nineteenth century, or the beginning of the twentieth century. Thanks to the analyses performed, documentation of historical textiles, and material characterization were performed, also deterioration products formed over time were detected.

One of the aims of this study is to determine whether there is a difference between the textile objects produced in different periods. The sixteenth century is a period when the Ottoman Empire was on the rise, and this shows itself in almost every field, as well as in the materials used in textile production. In textile objects, this situation is seen in the quality of weaving and material, the variety of patterns, the choice of dye, the intensity of the use of wire or metallic thread, the winding density of metallic threads, and the chemical content of wire or strips in metallic thread. This study also showed that the magnificence is evident in the textile objects of the sixteenth century when the Ottoman Empire was at its peak. At the same time, it was determined that there was a decrease in the use of materials, quality, and chemical content of materials in fabric production in the second half of the nineteenth century/the beginning of the twentieth century, which was the dissolution period of the Ottoman Empire.

In this study, it was determined that various types of deterioration occurred in most of the palace weavings examined, both with the help of observations and analytical methods and techniques. It is understood from this that these objects examined suffered from deterioration caused by unfavorable surrounding environmental conditions.

Before the conservation work is applied to historical textiles, the entire textile structure and the materials used should be defined with the help of various analysis methods and techniques. After determining the type and source of deterioration in a historical textile, the nature of the necessary preventive conservation methods will also be determined. For this purpose, keeping the environmental conditions at an optimum level, providing suitable environmental conditions, periodically auditing the provided conditions, and taking preventive measures when necessary are the primary principles. All these results show that analytical methods and techniques are necessary to begin the conservation and restoration works on textile objects, which are cultural heritage objects. This starts with observation and documentation and then goes to the type of intervention methods and material selection.