An Applied Study on Using Laser for the Conservation of an Archaeological Textile Embroidered with Metal Threads at the Museum of the Faculty of Applied Arts, Helwan University (No. 121/5)

There is an urgent need to use laser cleaning for a complicated textile because it is an effective technique for metal artifacts. It offers a high degree of control, especially in cleaning fragile and very detailed artifacts (Abdel-Kareem & Al-Saad, 2007). The inherent unique properties of laser light, such as intensi-ty, monochromaticity, directionality, and coherence, have made lasers effective tools in a variety of applications in the industrial and biomedical fields. Fur-thermore, a good understanding of the phenomena happening at the interaction of laser radiation with materials is fundamental for the success and opti-mization of any laser-based application. Therefore, laser cleaning depends on the nature of the material to be removed (Fotakis, Anglos, Zafiropulos, Geor-giou, & Tornari, 2007). The study adopted Q-switched Nd:YAG laser, which is the most common type in conservation. It employed investigation and analysis devices, such as SEM-EDX, XRF, and XRD.


Introduction
Precious metals have been used for the decoration of textiles since ancient times to create luxury objects for the secular and religious elite. Metal threads have

Artistic Description of the Archaeological Textile
The monument is a piece of a squared red silk textile decorated with flying birds. The external frame and above the flying wings of the birds are beige, suggesting dense feathers. The birds are light beige, but the head is not clear enough. Furthermore, the background is decorated with floral motifs in the form of curled plant branches like semi-circles. Some branches have brown leaves surrounded by three-leaf and four-leaf light beige flowers in some parts. These brown branches dominate the four corners. In addition, some leaves are near the tail of the bird in the form of dense down-up branches that come out of a hidden stem because of the abundant (dark) brown leaves (are shown in Figure 2). The brightness of the brown color disappeared due to accumulations of aerosols, especially in the leaves.
There are many floral paintings in the form of a dark brown stem on a dark white background. The stem was somewhat shining before cleaning. In the lower part of the stem, there is a single leaf topped, from the other side, by three flat leaves with a dotted white corona reflecting them on a red background. It is topped by two leaves out of the stem. A part of the lower leaf is covered by the upper one. On the left, there is a bigger leaf linked with the head of the bird. The stem ends with two emerging small stems with three leaves each. The main stem is topped by a set of single or overlapping leaves like the end. The leaves are encircled by a shadow or a dotted white corona showing the leaves properly.   These signs suggest the artists' link with the nature and ability to create a special one as shown in the art and depictions on this textile. When considering these light brown birds on a red background, two dimensions appear, even if the artist tried to integrate a simple part of the third dimension of the wings by highlighting the feather, taking an inclination in line with the flying wings. The artist did not adopt the three dimensions completely in depiction and modified the basic shape of birds. However, this did not show a lack of skills. Rather, it is a philosophy.
Since ancient times, the philosophy of modified art has appeared. It was clear in the era of Akhenaten of the New Kingdom when colossal sculptures, wall paintings, and papyri differed from the stereotyped nature of the masculine body that had feminine qualities. In implementing the artworks of Akhenaten, the artist always adopted certain ways to create an intersex form.
Furthermore, modified artifacts appeared in Coptic art, especially in the early period. The Coptic artist modified artworks significantly, which affected the Coptic textiles, especially tapestry. For example, the paintings were modified to be semi-human, semi-animal, and semi-bird. This was not because of the poor skills, but the Coptic artist who inherited the great Ancient Egyptian civilization had a religious and artistic philosophy. It might be due to the artistic features of the time.
In the early Islamic era, the modification of artworks was significant for religious purposes because painting and sculpture of the people and the animals were prohibited or undesirable. Therefore, the Muslim artist did not depict nature. Instead, he modified it greatly or adopted floral motifs and Arabic scripts.
If he used human and animal depictions, he made significant modifications to the dimensions. Thus, he benefited from the Sasanian and Ancient Near Eastern arts that were ruled by the Muslims. The artists in these areas modified their artworks based on imagination in deducing the shapes of animals or combining animals and birds. In the present artifact, the artist made substantial modifications to the birds.
He implemented them using a needle accurately, illustrating significant skill in implementation using metal threads. The selections of colors were successful.
For example, the vivid red background attracts attention. Once seen, the artifact seems to be a unique colorful figure with its vivid and attractive red color. It shows a whole life with the reflections of the rainbow. The textile was implemented in a creative manner artistically. In terms of color selection and dimension, many eastern artistic traditions united, including accuracy, floral motifs, modified birds to mirror the spirit of the nature-loving artist. For example, birds were modified with unique flying wings to enrich the textile.
The tails had slight bowing, affirming the birds' stable movement. The coherent and stable movement of the wings and tails suggest that the birds are aware of their objectives. Furthermore, the birds' direction indicates the unity of objectives. Their coherent and stable movement suggests complete understanding in these places and familiarity with their positions.
Although the dimensions of birds are not atypical in terms of embodiment because of modifications and being 2D only, the dimensions between the body, tail, wing, and head were modified by the artist and differed completely from nature. The artist could create an amazing picture of the embodied birds moving towards a certain objective. Studying the stand of the textile illustrates that it is made of hard white wood and measures 120 cm × 120 cm, but the textile measures 85 cm × 90 cm. The textile is fixed on a linen cloth on a wooden stand with external square wooden corners with a periphery of 4 cm × 4 cm × 4 m × 4 cm. Additionally, the wooden corners were supported in the middle with two white wooden planks with a periphery of 2.5 cm × 3.5 cm × 2.5 cm × 3.5 cm to support the surrounding blanks containing the cloth holding the textile. The first blank is about 37 cm to the right of the external frame, while the second one is 36 cm to the left of the external frame. The frame is cross-fixed in the middle with a wooden blank that measures 2.5 cm × 3.5 cm × 2.5 cm × 3.5 cm in order not to bend over the archaeological textile (see Figure 3).
The archaeological textile is fixed from the corners in the middle area of the linen cloth using magic stitches of a mean thick red silk yarn. It contains metal threads on a pale green background appearing from some lost parts. In the right low part, a large area and some small areas of the metal threads used to implement the paintings are lost. However, the background is almost complete, but with accumulated dirt and dust affecting the main color and turning it pale. Therefore, the green color is light and covered with much dust and dirt caused by air pollutants.
Many metal threads appear single and stretching down-up due to the loss of many metal threads connected with them. Some threads are slope, and others appear in the parts of the archaeological textile as they are disconnected from the others that lost integrity on the background. They are soft single hairy yarns.

Deterioration Manifestations in the Artifact
The artifact has some deterioration manifestations, including lint in some parts and fading of the background color because of the inappropriate folding and storing. Consequently, the textile appeared as four attached pieces. A soft layer of dust and dark deposited aerosols covers the artifact, causing severe darkness of the metal threads (see Figure 4). There were clear color changes in the background that appeared because of losing parts of the layers.
There were some hard calcifications on and between the metal threads and inside the textile structure. The textile was harder and less flexible because of the deposited pollutants, dust, and aerosols, as well as humidity that integrated the granules and created hard micro-layers on the metal threads, between the textile structure, and on the background. Because of the high relative humidity and lack of good ventilation tools, some dyes, especially red, caused pale red spots on the weak green background. Furthermore, humidity dissolved some aerosols and dust from the polluted environment surrounding the Museum. is appropriate for maintaining flexibility. When SO 3 interacts with some internal textile humidity, the textile has relative dryness and some parts break down (are shown in Figure 5), especially when handling or treating the textile.     The stand dried, and its color was dark significantly because of dirt and aerosol depositions. It was handled with mechanical and laser cleaning.

Laser Techniques and Applications
Cleaning the composite textile objects is very problematic and requires safe and accurate methods (Elnaggar et al., 2015). The cleaning techniques may be harmful to the metal and textile. Thus, the metal threads are often not cleaned (Hacke, Carr, & Howell, 2003). Many mechanical and chemical treatments were utilized to clean metal threads on the archaeological textile. However, it is highly recommended to avoid mechanical cleaning methods for metal embroidery threads because of their devastating results that they may remove the noble patina and the coating layer on the cleaned surface. Instead, various materials and methods could be used. Most of the chemical treatments commonly used for cleaningmetal threads are incompatible with the metals and the organic fiber's core, and it is almost impossible for the cleaning solution to avoid contact with the fibers (Abdel-Kareem & Harith, 2008). Therefore, chemical and mechanical cleaning methods are rarely applied in the case of the coated organic materials (Járó, 2009).
The deterioration of metal threads in textile is a complicated problem that cannot be solved by the classical conservation methods. For example, the immersion taking place in chemical or electrolytic corrosion cleaning techniques may damage the fibers and dissolve any dye, while mechanical cleaning may remove the painting.
On the contrary, modern technology application has proved more effective than the traditional methods in the conservation of cultural heritage. Laser is one of the most significant techniques in cleaning, but it is still being examined because of the complexity of rays and the different materials of the textile with metal threads (Radojkouić, Ristic, Zrilić, & Suzana, 2015).

Materials and Methods
At this study used some methods Mechanical cleaning, Laser cleaning (see

XRF Analysis
Identifying the chemical composition of all samples was carried out by the X-Ray Fluorescence Analysis (XRF), JEOL JSX Element Analyzer with Energy Dispersive X-Ray Fluorescence system (EDXRF). It helped analyze and identify the components of corrosion.

XRD Analysis
XRD Unit, Assiut University, Model PW 1710 control unit Philips, Anode Material Cu, 40 kV, 30 mA, 2 Cita from 4 to 60 was employed for analyzing the samples and identifying their components. It was applied to a two-layer textile embroidered with metal threads and beige metal decorations on a background of red silk. The simple mechanical cleaning using different brushes was adopted. The stand and the textile were cleaned mechanically in an area of good ventilation in order to make the textile fibers acquire humidity.
The content of relative humidity was increased indirectly through evaporating the surrounding area for many days using a spray far from the textile and the cloth stand. As a result, the textile fibers are wet appropriately to facilitate physical and laser cleaning.
Q-switched Nd:YAG lasers device was used to provide very short pulses of high energy and TEA CO 2 laser that was employed successfully to remove the painting (Koh & Sárady, 2003). In the case of 1046 nm wavelength, the metal surface changes and various colors, including orange, red, yellow, and blue, appear. The thermal contributions or effects when using 355 nm ultraviolet rays that are very small do not change the color surface (Ristic et al., 2014). Consequently, deteriorations were removed successfully from the silver surface in wavelengths of 532nm and 266nm. However, 1064 nm wavelength was inappropriate because they might cause metal melting, as well as cutting and burning the fibers (Koh, Lee, & Yu, 2003).
Laser cleaning is always related to one of the two types of damage to the surface of the metal. At high energy, deterioration takes place in the form of surface melting. At low energy, the original oxide layer turns into adhered drops of melted metal (Koh, 2005 (Elnaggar et al., 2015). Green laser 2 (Q-Switched Nd:YAG Lasers) of 352 nm wavelength was used (Koh & Sárady, 2003). The archaeological textile was treated using agreen laser for 10 minutes that resulted in good and appropriate results for both the metal threads and silk. It did not cause severe heating like the other types of laser employed in the experimental study, such as (Infrared laser of 1 -64 nm wavelength, Ultraviolet laser of 355 -266 nm wavelength) in terms of affecting the textile fibers.

B 3. Results
Laser cleaning achieved good results in cleaning corrosion products, including Cl, Al, Ca, and Fe without affecting the metal threads or background see ( Figure   9, Figure 10). They were revealed by SEM-EDX, XRF, and XRD analyses.

Discussion
Results of EDX analysis shows the difference in the archaeological sample before and after laser cleaning, as well as the effect of laser cleaning on Cl, Al, and Ca.  Table 2, Figure 11, Figure 12 and Figure 13).
Results of XRF analysis of the first sample of archaeological textile illustrate a high percentage of CuO (70.831%). There are also small amounts of CaO (1.062%) and Ag 2 O (28.107%). The second sample of the treated textile shows a high amount of CuO (68.557%) and small amounts of CaO (0.897%) and Ag 2 O (30.546%) (see Figure 14, Figure 15).
Results of XRD analysis of the first sample of archaeological textile that is not deteriorated illustrates Cu as a major compound and Ag as a minor one. The second sample of the textile cleaned by laser shows Cu as a major compound and Ag as a minor one. Other resulting oxides appear, highlighting the effectiveness of laser in cleaning the archaeological textile (see Figure 16, Figure 17).
Sewing Support After laser cleaning, the lost parts, lint, and external edges were fixed using silk yarns with colors close to those of the textile fibers (dark red-dark green-light beige-olive green) using herring bone stitch, Z-Whip stitch, Laid-couching and slip whip stitch, as well as edges and hole whip stitches (as shown in Figure 18, Figure 19, Figure 20). Consequently, the textile is ready for sorting and exhibiting (are shown in Figure 21).    Figure 11. A difference in the archaeological sample before and after laser cleaning.