Introduction
Imagine a flannel robe against your skin, so soft that you can hardly feel its touch. Tightly wrapped, you are at ease, surrounded by comfort and warmth. The softness your robe provides is born of the cotton fibers making up the flannel fabric. Cotton fibers are flexible, convoluted strands which, when woven together, create a material perfectly suited for wrapping around the body. While you may be able to feel the effects of the cotton fibers in your flannel robe, they are impossible to see with the naked eye, and their coiled shape is visible only under a microscope.
Microscopy is an irreplaceable tool in the identification of textile fibers. With a powerful lens, it is possible to observe the characteristics of individual textiles. While the microscope has been around for some time, students still find the process of seeing the textile world up close fascinating. Dating back to the seventeenth century, the microscope has evolved to become an important tool in scientific observation. Cornelis Drebbel, Zacharias Janssen, Galileo Galilei, and Robert Hooke are some of the scientists credited with the invention and development of microscopes. Robert Hooke's book, Micrographia, published in 1665, depicted his microscopic observations and was one of the best sellers of that time. However, the adaptation of microscopy was greatly impacted by Antonie van Leeuwenhoek (1632-1723), a Dutch fabric merchant. Referred to as "the Father of Microbiology," he was neither a biologist nor the inventor of the microscope, though he is responsible for some of the greatest improvements to the tool. Prior to Leeuwenhoek's microscopes, microscopic images were distorted and hardly captured the details of what was observed. With the release of his improved microscope, biologists and scientists of the time hardly believed what could be seen. He handmade each microscope and inspired the creation of some of the first hand-held microscopy tools (see Figure 1). Most notably, Leeuwenhoek is known for keeping a detailed record of his findings. He drew sketches of tiny organisms, which he titled animalcules that we call microorganisms today. Leeuwenhoek and his microscope were the first to explore the microscopic aspects of the world we live in, studying everything from the size of bacteria to the blood flow in small vessels [1]. Antonie van Leeuwenhoek's work was amazing, but as with any new scientific observation, true biologists were skeptical.
Figure 1 Antonie van Leeuwenhoek started his career as fabric merchant and later inspired the creation of hand-held microscopy.
Source: Reproduced with permission of National Academy of Sciences.
When Leeuwenhoek was only 16, his mother arranged for him to begin an apprenticeship with a Scottish cloth merchant in Amsterdam. This became the first place he used a simple magnifying glass. While it could only magnify 3×, he was absolutely fascinated by the viewing and identification of fabrics and fibers. The fabrics were yarn-type and woven, and Leeuwenhoek learned that a close examination of a fiber under a magnifying glass could reveal a great deal about the fabric's properties.
A cloth merchant's primary responsibility was to closely check fabrics and determine their quality and value. In the seventeenth century, there were no manufactured or synthetic fibers. The only fabrics on the market were made of natural cellulosic or protein fibers. The cellulosics seen were primarily linen, cotton, hemp, nettle, and jute, and the proteins were wool and silk. To tell cotton from linen, or high-quality wool from low-quality wool, a cloth merchant needed a closer look. Antonie van Leeuwenhoek's curiosity grew out of this textile observation process. He would inspect fabrics for damage by mold or other infestations, or note the quality of dying. If he finds that a dye had not fully penetrated through the yarn or fibers, then the quality of the fabric would be deemed worthless. Becoming a cloth merchant required a deep understanding of textile fabrics, typically acquired over time through an apprenticeship. Working with textiles was a challenging job, and required proper training, even in the seventeenth century. The experience Antonie van Leeuwenhoek acquired in his lifetime allowed him to construct lenses and microscopes that permanently changed microscopy. While he never revealed his methods of creation, one is sure to remember that he was not only a great tradesman but also an amazing scientist and craftsman.
The microscope, as we know it today, has greatly advanced because of Leeuwenhoek, with amazing improvements in the nineteenth century, including the development and adaptation of the lens. An important contributor to lens development is Carl Zeiss, a German mechanic who partnered with scientists Ernst Abbe, a physicist, and Otto Schott, a glass chemist to create a better resolution technique. The heightened resolution improved the quality of microscopes, inspiring extensive improvements during the past 200?years.
1 Types of Microscopes Used in Science
Today, the microscope is commonplace, a simple instrument present in every laboratory. However, microscopes have come a long way, and their viewing and functioning properties have become quite complex. A variety of microscopes are used for specific purposes in scientific laboratories. Most of these use photons to form clear images and are called light microscopes. Electron microscopes, specifically the scanning electron microscope (), are used in large-scale, full-service laboratories. These microscopes have a massive range of magnification allowing scientists to analyze fibers in a way that light microscopes cannot. SEMs have a very high resolving power and the ability to perform elemental analyses when equipped with an energy- or wavelength-dispersive X-ray spectrometer.
Microscopes can be differentiated by comparing the images they generate. The physical principle utilized by a microscope is equally as important, as it will usually determine why fiber images differ when viewed using different microscopes. Different microscopes visualize different physical characteristics of the sample. Resolution and magnification, which will be explained later in this section, are to be taken into consideration. The most common magnifications used by students to enlarge a fiber image are 4×, 10×, 40×, and 100×.
1.1 Stereomicroscope
The stereomicroscope is one of the simplest and easiest types of microscopes to use. It works by bouncing the light off the surface of the specimen rather than transmitting it through a slide. They are primarily suitable for observations not requiring high magnification. Its low magnification power (ranging from 2.5× to 100×) is due to its design. This microscope's illuminators can provide transmitted, fluorescence, brightfield, and darkfield reflected imagery, which allows the viewing of microscopic features that may otherwise be invisible.
With the stereomicroscope, there is a large gap between the specimen and the objective lens, which provides an upright, unreversed image. This space allows for better specimen manipulation and for a basic microscopic analysis to serve as the perfect preparation for a future, more detailed, microscopic examination and analysis. One important advantage of this scope is that the specimen does not require any special or lengthy preparation prior to observation. The specimen is simply placed under the lens and observed as needed.
The stereomicroscope is well suited for use in the preliminary identification of fibers, yarn, and weave structure when observing dated textile pieces for conservation practice. In general, textile fibers must be extracted from a yarn for proper observation and identification, but in viewing and identifying old textiles, such as tapestries or fabrics preserved for many years, removing fibers would damage the piece. With this microscope, the entire untouched, unraveled piece may be viewed without damage. In addition, this piece of equipment can be attached to a separate boom stand, allowing movement over a large object for examination. If a conservationist wants to examine the fibers of a new museum tapestry piece, a video camera may be attached to this microscope for proper record-keeping. Later chapters will include the conservation of textiles.
1.2 Compound Microscope
The compound microscope, also known as the optical or light microscope, uses light and a series of lenses to magnify particularly small specimens. Compound microscopes were invented in the seventeenth century and vary greatly in simplicity and design. These microscopes can be very complex and are a considerable improvement from the aforementioned stereomicroscope. While stereomicroscope can only magnify up to around 100×, compound microscopes rise in resolution and magnification up to 1300×. Today, the use of reflected light in microscopy outweighs the use of transmitted light. Regarding fiber examination, light microscopes are suitable for the analysis of fiber anatomy in hair fibers, such as the different types of medulla.
1.3 Polarizing Light Microscope
The polarizing light microscope is undeniably an advanced and versatile piece of equipment. It is normally equipped with a round, rotating stage, a slot for the insertion of compensators, and a nosepiece. It stands out from other microscopes due to its preciseness in both qualitative and quantitative fiber analyses. It embodies the functionality of normal light...
