**1. Introduction**

**Citation:** Łucejko, J.J.; Vedeler, M.; Degano, I. Textile Dyes from Gokstad Viking Ship's Grave. *Heritage* **2021**, *4*, 2278–2286. https://doi.org/10.3390/ heritage4030129

Academic Editor: Lucia Burgio

Received: 21 July 2021 Accepted: 6 September 2021 Published: 8 September 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

The production of natural dyes for textiles was an important economic factor in the early Middle Ages, and a number of written sources mention the production of madder for sale [1].

The period between ca AD 750–1050 is called the Viking Age in Scandinavia. This was a time when people from Norway, Sweden, and Denmark first began travelling to other parts of the world on a large scale and established themselves as a political factor in Europe. Profound social and political change took place in that period, when old religious ideas gave way to new ones and when the Scandinavian countries gradually became unified kingdoms [2]. The impact of long-distance trade and the establishment of urban trading settlements played an important role, bringing the Scandinavians into contact with foreign cultures all over the old world. New trends in arts and crafts fueled the expansion of long-distant trades, including textiles and dyestuffs [3–5].

Given the expansion of the Scandinavian cultural and commercial routes and possible degradation processes that have affected the textiles, it is not easy to predict which could be the natural dyes originally used in the samples retrieved from archaeological sites. The best-preserved textiles from the Viking Age come mainly from bogs or mound contexts. The textiles found in the bogs constitute one of the largest and best-preserved collections of textiles in existence [6]. The chemical study of these fabrics has permitted the identification of a narrow range of natural dyes used in these times. Plants containing luteolin, indigotin, and alizarin were determined in textiles from Søgårds Mose II and Skærsø [6]. These components of natural colorants were also frequently reported in the studies performed by Walton P. Rogers on a wide number of textile samples from the Viking Age, along with insect dyes and lichen purples [7–9]. The earliest use of indigotin in Scandinavia dates back to Rebild, Denmark, dated between the 4th and the 3rd century BC, while the earliest evidence of the use of alizarin-containing madder dye in Scandinavia is dated

to the 1st century BC, and was assessed in the textiles collection from Skærsø [10]. The Scandinavian finds indicate that madder became a common dye source in Scandinavia during the Migration period (AD 400–520/540) [11].

Another source of well-preserved textiles are mounds. Some people in the uppermost social strata of society were at this time buried in ships, which were then placed in a large burial mound. The Oseberg ship, on the board of which the bodies of two women with very rich grave goods were found, is one of these. A rich array of textiles, both woolen and silken, designed for a range of uses, were unearthed within this discovery. A very important ship grave, dating to around 900 AD, was also found in Gokstad, Norway [12]. Various textiles from this grave were in good preservation conditions and included an outstanding embroidery in silk and gold (see Figure 1). The same technique has been used in embroideries found in other Scandinavian graves from this period, but the patterns found in these graves are very different [13]. The embroidery from Gokstad is formed in a flower pattern by using a combination of a gold-thread with a silk-core and threads made of pure silk. Traces of a red color are still visible on the thread used to stitch down the gold lamella. When studying the flower pattern in a stereo loupe, it looked like a red and a golden color have been used in combination to form a polychrome pattern [14]. Remnants of a ship's tent were also found in this grave [15–17]. The remnants consist of some 150 fragments of coarse 2/2 twill textiles made of wool, intervened with fragments of rope. Some of the textile fragments bear traces of red color, while others look undyed to the naked eye [14].

**Figure 1.** Photographs of the embroidery in silk and gold found in the ship grave in in Gokstad, Norway. Picture by Ellen C. Holte, Museum of Cultural History, UiO.

The most used method for the analysis of dyes in archaeological artefacts is liquid chromatography (HPLC) with different detectors, which, after a suitable sample treatment, allows the separation of the colored molecules and the identification of the original dyes used. The most common setup is HPLC with spectrophotometric detectors, in particular, diode-array (DAD), because it allows the reliable identification of several dyestuffs by comparison with the profiles of reference materials [18]. In the past 15 years, HPLC coupled with mass spectrometry (MS) has been successfully used for dyes analyses, providing a higher sensitivity than HPLC-DAD, which is particularly useful in the analysis of archaeological textiles, where the sample is usually small in size and contains low concentrations of time-altered colorants (see, in general, [19–21]). HPLC-MS also allows, thanks to the acquisition of tandem mass spectra, us to identify unknown species, thus providing information

on dyes not available as reference materials [22–24]. Different reversed phase analytical columns have been employed for dyes analysis with mass spectrometric detection, differing in the length of the hydrophobic chains (C8 or C18), particle size (also capillary columns were employed), and end capping, or even presenting polar embedding, such as RP-amide columns [23,25]. Recently, two-dimensional liquid chromatography was also employed successfully [26].

One of the most important steps in dye analysis is the extraction/separation of the analytes from the sample. The primary objective of the sample treatment is to find the conditions in which the maximum extraction yield and minimum alteration of the molecular profile are achieved, as reviewed in [27,28]. Most extraction methods are thus based on complexation with organic acids such as formic, oxalic, or acetic, alone or combined with EDTA, where mild extraction takes place [29,30]. Various organic solvents have also been applied for the extraction of less hydrophilic compounds, e.g., dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and pyridine [31]. Finally, whenever the mild extraction does not provide any result, harsher hydrolysis treatments may be applied, which were quite diffused in the past, but contraindicated for labile colorants and/or materials unstable in acidic conditions [20,31,32].

This study presents the results obtained for a set of textile samples collected from the Gokstad Viking ship's grave. The identification of the coloring materials was achieved through the application of three increasingly harsh extraction procedures, based on dimethyl sulfoxide, EDTA with DMF extraction of the dyestuff from the yarns, followed by a hydrolysis in acidic condition of the residue; the analysis of the extract was performed with high performance liquid chromatography (HPLC) with diode array detection and subsequently confirmed with HPLC coupled with a high resolution mass spectrometric detector (ESI-Q-ToF). The study led to the identification of the molecular markers of a relevant dyestuff used during the Viking Age.

#### **2. Materials and Methods**

#### *2.1. Samples*

Samples of colored textiles were subjected to specific procedures to extract the characteristic markers of the materials used during dyeing. The extraction procedures applied are specific for the target molecular markers for each sample and are described in detail in Section 2.2. Table 1 shows the samples information, the extraction procedures chosen, and the instrumental methods applied.


**Table 1.** Description of the samples.

#### *2.2. Analytical Procedures*

Three analytical procedures were applied to extract the colored compounds present in the textiles studied. The conditions of each procedure applied are reported below.

#### 2.2.1. EDTA/DMF Procedure

A mild extraction by dimethylformamide (DMF) and 0.1% Na2EDTA 1:1 (*v*/*v*) was first applied. Then, 200 μL of mixture solution were added to the sample; extraction was performed at 60 ◦C for 60 min in ultrasonic bath. The supernatant was filtered with PTFE filter (0.45 μm) and injected in the chromatographic system (20 μL). The procedure is particularly useful to detect the presence of labile components and in case of fragile materials and degraded textiles [33].

#### 2.2.2. DMSO Extraction

A specific extraction by dimethyl sulfoxide (DMSO) to maximize the recovery of indigoids, and in particular, of photo-labile brominated indigoids, was applied to the yellow faded sample S2, since no hints on the original color could be drawn. The procedure consisted of an extraction assisted by ultrasounds at 60 ◦C for 5 min followed by filtration with PTFE syringe filter (0.45 μm). The sample was kept in the dark for 5 min and then injected into the chromatographic system.
