Introduction
Textile fibers, in the development of humanity, have had different and very varied uses. In ancient times, cultures such as the Egyptians embalmed their dead in fabrics such as linen, and Asians used silk to make their most expensive clothing. Regarding the use of fabrics as a paint support, many have been the fibers used. The first works carried out on textile supports date back to the mid-15th century and became the most widely used support in European painting since the 18th century. Due to their fundamental function as "base" of the pictorial layer, the textile fibers are embedded in a layer called the preparation base,on which the plastic artist in turn prints the different layers of pigments and binders that are determined by different techniques and due to their sequence allow the artist to finally express the plastic work.
On certain occasions, the paintings show signs of deterioration due to different factors, such as the loss of consistency and elasticity of the support due to aging, its oxidation due to nails or the oxygen in the medium, and the presence of microbial growths that can degrade cellulose; signs that suggest to restorers, conservators and heritage specialists the performance of intervention processes on these damaged works.
Textile fibers. Classification.
There are several natural and other artificial fibers that are used in the manufacture of textiles; which depending on their chemical composition can be grouped as follows:
- Animals: Natural silk, Wool, Camel hair, Alpaca, Llama, Mohair, Kashmir, Angora, Rabbit, hare, Reindeer, Bison, Mink, Beaver, Nutria Vegetables: Cotton, Coconut, Linen, Ramie, Jute, Hemp, Sisal, Esparto.Minerals: Asbestos, Metallic threads, Rubber.
Its properties contribute to the characteristics of the fabrics, that is why investigations are normally started determining the fiber content; considering as fundamental aspects: the external structure, the internal structure and its chemical behavior. In the external structure its length, diameter, size or denier, cross section, surface contour, curl and fundamental parts are analyzed.
The analysis of the chemical composition allows classifying them according to the chemical nature of their origin, eg. Cellulosic, acrylic; being the factor that allows to determine if they originate from a single compound, from two or more. It also allows identifying the orientation of the molecular chain of each fiber, which makes it possible to know when a fiber is oriented (its molecular chain is parallel to the longitudinal axis of the fiber) and when it is amorphous (the fiber is randomly distributed). This analysis also includes: the abrasion resistance of the fiber, its absorbency or humidity rate, elastic recovery, its resistance and resistance to sunlight, among other properties.
Fiber identification
The process of identifying a fiber generally depends on the nature of the sample, the experience of the specialist performing the process, and the equipment available. There are several identification methods, although those with less complexity and can be carried out with a lower technological requirement are the following:
- External visual examination of the sample. Flame combustion tests. Microscopic analysis of the longitudinal and cross section.
Additionally, other methods such as Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM-EDX) and gas chromatography (GC) ¹ can also be used. These determinations facilitate very safe procedures to distinguish not only the main chemical types of fibers, but also closely related fibers; that they only have small differences in their physical, chemical and structural properties. It should always be taken into account that when a fiber is to be identified from a textile support of a work of art, a very small amount is possessed; therefore, special care must be maintained when handling the sample.
Visual exploration
It includes the analysis of the appearance and response to the touch of the fiber, its length, its body and texture, its luster and its opacity. In this type of observation they can be counted additionally, without extracting samples from the support; the amount of threads present in 1 cm of the fabric, according to the weft and the warp of it¹.
Combustion test
It allows to identify the chemical composition of the fiber and the group to which it belongs; although it has the disadvantage of not being able to be applied when a mixture of fibers is presented. Includes serial tests:
- Approach the fiber to the flame: Take a few fibers with tweezers, and without touching them, bring it closer to a non-luminous flame. See if they melt or contract. On the hot plate: Place the fiber in a glass of potassium nitrate on a metal plate, which can be heated to melt the glass. Observe if the fibers melt or char, after separating them with a needle. In the flame: Place the fibers in a weak flame. Observe if they burn and write down the smell produced².
Analysis under the microscope
It allows knowing the structure and studying the probable differences within the same group, being much more effective for natural fibers than for synthetic fibers; due to the fact that in the latter there is a great similarity and their own manufacturing process can cause contrasts ³. The sample is examined under a microscope longitudinally with n-decane as a binder and for the cross section the fiber is placed in a block of polyester resin. Useful aspects to consider in this exam are:
- Scales, irregularities of size and shape in the longitudinal axis of the fiber, growths and knots of the fibers, presence of few many striations along the axis, color differences, differences in the shape of the cross section².
Fibers most used as textile support. Its main characteristics.
Throughout our own history, artists have employed a diverse number of textile fibers as supports for their artwork. The Venetians are the first to use the fabric on a regular basis and because it is more mobile and less heavy than wood as a support, it is better adapted to large formats. The oldest supports were made of natural fibers (hemp, linen and cotton) although they are also made from synthetic fibers today.
Cotton
It is obtained from Gossypium, from the mallow family and is considered one of the most used fibers, due to its properties. It was probably not used in works of art until the 19th century, although in modern painting it is used as a support, for entelar and as a patch.
After subjecting the fibers to the analysis under the light microscope, it is possible to define the parts of their general structure. It is formed by cuticle, primary wall, secondary wall and a lumen. The cuticle is a layer that covers the primary or external wall. The secondary wall is made up of cellulose layers, which are in turn made of spirally distributed cellulose chain fibrils. These inverted spirals are important in elastic recovery and fiber elongation. The lumen is also called the central canal, by some specialists, and through it the nutrients are transported during the growth stage.
It contains carbon, oxygen and nitrogen and reactive groups (OH). It deteriorates with acids, although alkalis do not damage it as much. It supports chlorine bleaching and is resistant to organic solvents. It oxidizes with sunlight, turning yellow and with fiber degradation. It burns easily and as it has weak hydrogen bonds, the fabrics made from this fiber wrinkle³.
The concept of canvas designates for linen or hemp fabrics. With very few exceptions, until the 60s of the 20th century, these fibers were used exclusively for the patterning and patching process in restoration work on damaged works, although nowadays synthetic and glass fibers are also used for these processes. fabric mix.
Linen
It is obtained from the stem of Linum usitatissimum L. It is one of the oldest fibers, being partially displaced by cotton as mechanization of the latter arose. Its fibers have a more oriented molecular structure than cotton, making them stronger. It has low elasticity and flexibility. It is resistant to alkalis, organic solvents and high temperatures. It is more resistant to sunlight than cotton ³. Upon light microscopic observation, the primary fibers are made up of very pointed cells, with thick walls and a small lumen. It has nodules, usually X-shaped transverse dislocations, which can be better observed if the fiber is embedded in liquid paraffin. The walls have a spiral structure².
Hemp
It is derived from the stem of Cannabis sativa, it is closely related to flax because it is also native to temperate climates. Its elemental fibers resemble flax in dimensions and overall appearance. Under the light microscope, the outer fibrils of the cell wall follow a Z-turn, counterclockwise and counter-clockwise. In its ashes, after complete combustion, and if it has not been boiled or bleached; crystals should appear.
Jute
It is obtained from the bast of the plants Corchorus capsularis and Corchorus olitorius. The fiber appears along the stem of the plant, in the form of a ring mass. When observing its cross section under the microscope, thick-walled polygonal cells with a central channel in each are found. On longitudinal examination the ends may be pointed².
Synthetic fibers
These fibers have greater resistance to breakage, rubbing and better dilation. In general, they wrinkle little and are more stable against water, light, weather, chemicals and insects. Polyamide fibers such as nylon and perlon are considered the most important, although the use of polypropylene fabric to make some fabrics has been reported since the 1960s. Glass fiber fabrics are fabrics of mineral origin, resistant to humidity, light and the action of animals and plants. According to Mayer, they were used in the 30s of the 20th century and in 1961 they were proposed by Boissonnas to make cloths replacing linen. When used in restorations of works supported by other fibers, glass fibers do not have the same shape and do not allow smoothing.
Conclusions
Knowledge of textile fibers, their classification, identification and main characteristics; when used as a support in the works, it allows the conservators, restorers and other specialists together with the care and safeguarding of the heritage to carry out interventions on the pieces in an accurate and quality way, minimizing economic expenses and thus guaranteeing the principle of minimum intervention..
Bibliography
- Gómez González, Mª Luisa. Scientific Exam applied to the conservation of works of art. ICRBC. 1st ED. Madrid: 1994.Identification of textile fibers. Spanish ED. Blume Publishing. Barcelona, 1968. Toca, Teresa. Fabrics: Conservation, restoration. Polytechnic University of Valencia, 2004. Cennino Cennini. The Art book. ED Akal, Madrid, 1988. PL Bouvier, Manual des jeunes artists et amateurs en peinture. Paris- Strasbourg, 1827.K. Nicolaus. Frame Restoration Manual. 2004.R. Mayer, The artist´s handbook of materials and techniques. New York, 1963.AG Boissonnas, “Relining with glas-fiber fabric”. Studies on Conservation, 6.1 1961, p 26-30.
