B. Light Microscopy Test:
A compound microscope capable of at least 200x magnifications is required for fibre identification. A magnification of 200x may be adequate for tentative identification,
especially of the natural fibres, but is not adequate for viewing the details of fibre structure.
The lens and objectives of the microscope, as well as the slides and cover glasses, must be
clean and free of scratches. The light source should be adjusted for maximum visibility prior
to looking at prepared slides. Have materials at hand to sketch the fibres viewed, and have
access to a source of photographs of known fibres to make comparisons for identification.
The following figure shows the longitudinal and cross-sectional views of the most common
fibres.
Longitudinal mounts:
It is possible to mount a single fibre, but it is less frustrating for most microscopists to use several fibres. A minimum of ten fibres is useful when the material to be studied is a blend.Too many fibres on a slide makes it difficult to focus on a single fibre to observe the details
of its surface contour. When taking a sample from a yarn in a fabric, untwist the yarn completely to separate the fibres. The basic steps for making a longitudinal mount are as follows.
1. Place a single drop of water, glycerine, or mineral oil on the center of the glass slide.
Mineral oil provides the best definition, but the other materials are adequate.
2. Carefully place the fibres in the drop of liquid with the length of the fibres parallel to
the long dimension of the slide.
3. Place the cover glass lightly over the drop of liquid and the specimen. Tap the cover
glass gently to remove air bubbles.
4. With the objective in its highest position, place the slide on the stage of the
microscope. Lower the objective carefully before trying to focus the slide. It is very
easy to damage the objective by scratching it or smearing it with oil.
5. Focus on low power and observe the fibre before focusing on high power. Note the
general shape of the fibre, then look at it carefully for signs of scales, convolutions,
pockmarks, striations, and other features. Look carefully to see if more than one
type of fibre is present.
6. With the microscope focused on high power, move the fine adjustment very slowly
to see if variations in surface contour are visible. Again, look carefully to see if more
than one fibre type is present
7. Sketch the fibres as seen through the microscope, then compare your sketch with
standard photographs to conclude which fibres might be present.
A compound microscope capable of at least 200x magnifications is required for fibre identification. A magnification of 200x may be adequate for tentative identification,
especially of the natural fibres, but is not adequate for viewing the details of fibre structure.
The lens and objectives of the microscope, as well as the slides and cover glasses, must be
clean and free of scratches. The light source should be adjusted for maximum visibility prior
to looking at prepared slides. Have materials at hand to sketch the fibres viewed, and have
access to a source of photographs of known fibres to make comparisons for identification.
The following figure shows the longitudinal and cross-sectional views of the most common
fibres.
Longitudinal mounts:
It is possible to mount a single fibre, but it is less frustrating for most microscopists to use several fibres. A minimum of ten fibres is useful when the material to be studied is a blend.Too many fibres on a slide makes it difficult to focus on a single fibre to observe the details
of its surface contour. When taking a sample from a yarn in a fabric, untwist the yarn completely to separate the fibres. The basic steps for making a longitudinal mount are as follows.
1. Place a single drop of water, glycerine, or mineral oil on the center of the glass slide.
Mineral oil provides the best definition, but the other materials are adequate.
2. Carefully place the fibres in the drop of liquid with the length of the fibres parallel to
the long dimension of the slide.
3. Place the cover glass lightly over the drop of liquid and the specimen. Tap the cover
glass gently to remove air bubbles.
4. With the objective in its highest position, place the slide on the stage of the
microscope. Lower the objective carefully before trying to focus the slide. It is very
easy to damage the objective by scratching it or smearing it with oil.
5. Focus on low power and observe the fibre before focusing on high power. Note the
general shape of the fibre, then look at it carefully for signs of scales, convolutions,
pockmarks, striations, and other features. Look carefully to see if more than one
type of fibre is present.
6. With the microscope focused on high power, move the fine adjustment very slowly
to see if variations in surface contour are visible. Again, look carefully to see if more
than one fibre type is present
7. Sketch the fibres as seen through the microscope, then compare your sketch with
standard photographs to conclude which fibres might be present.
Cross-sectional mounts:
Special plastic and metal plates are available for making fibre cross-sections. Special fibre microtomes are used for more sophisticated work. Where such aids are not available, it is possible to make a section using a piece of cork, a threaded sewing machine needle, and a sharp single-edge razor blade. The instructions follow.
1. Use a small piece of fine-grain cork no more than 1 em (0.5 inch) thick. Cut so that it
is flat on one side. The cork wedge should be of a diameter small enough to slice
easily.
2. Thread the sewing machine needle, and carefully force the point of the needle
through the cork until a loop of thread can be formed.
through the cork until a loop of thread can be formed.
3. Form a thread loop around your finger and pull the needle back through the cork.
The needle may then be removed; it was needed just to push the thread through the
cork to form the loop.
The needle may then be removed; it was needed just to push the thread through the
cork to form the loop.
4. Make a small bundle of fibre ti fit through the thread loop. Then, using the free ends
of the thread, carefully pull the looped fibre back through the cork. The fibre should
be packed firmly in the hole of the cork, and fibre ends will be visible on both sides
of the cork. After a little practice, estimation of the exact amount of fibre to use
becomes easier
of the thread, carefully pull the looped fibre back through the cork. The fibre should
be packed firmly in the hole of the cork, and fibre ends will be visible on both sides
of the cork. After a little practice, estimation of the exact amount of fibre to use
becomes easier
5. Place the flat side of the cork down on a cutting board and use the razor blade to cut
a thin slice perpendicular to the fibre embedded in the cork. The slice should be no
more than 0.5 mm thick. Make the cut with a single, continuous motion, not a
sawing motion.
a thin slice perpendicular to the fibre embedded in the cork. The slice should be no
more than 0.5 mm thick. Make the cut with a single, continuous motion, not a
sawing motion.
6. Place the cork slice on a glass slide. Do not use a mounting medium or cover glass.
Focus the microscope and observe the cross sections of the fibres.
Focus the microscope and observe the cross sections of the fibres.
Results: Look carefully at the shape of the fibre, and compare it with photomicrograph of known
fibres. Most natural fibres can be identified by simple light microscopy, but positive
identification of manufactured fibres is often difficult with this technique. When a fibre
blend is present, it is possible to approximate the blend level by counting the fibers.
Microscopy is also a good way to determine the number of fibres present in a blend.
fibres. Most natural fibres can be identified by simple light microscopy, but positive
identification of manufactured fibres is often difficult with this technique. When a fibre
blend is present, it is possible to approximate the blend level by counting the fibers.
Microscopy is also a good way to determine the number of fibres present in a blend.
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