This document discusses different types of microtomes and microtome knives used to cut thin sections of tissue for microscopic examination. It describes vibrating microtomes used to cut unfixed tissue, and different knife designs including wedge, plano concave, and biconcave knives made from steel or diamond. The document also covers knife sharpening techniques including honing with stones or plates and stropping to further polish knife edges.

1. MICROTOMY

2. VIBRATING MICROTOME
• Designed to cut tissue which has not been fixed, processed or frozen.
• Used in enzyme histo chemistry, ultrastructural histo chemistry.
• During sectioning the tissue is either immersed in water, saline or fixative.
• It is cut by a vibrating razor blade, at thickness generally greater than used for
paraffin wax.
• Tissues are cut at a low speed to avoid disintegration.

3. MICROTOME KNIFES
• Developed to fit specific types of microtomes and cope with different
degrees of hardness of tissues and embedding media.
• Knives are made of steel for Paraffin wax embedded tissues.
• Diamond or glass knifes are used cut resin embedded tissue.

4. KNIVES
• Knives are classified according to their shape
1. Wedge
2. Plano concave
3. Biconcave
4. Tool edged or D profile

5. WEDGE KNIFE
• Originally designed for cutting frozen sections
• Gives great rigidity to the knife
• Used for cutting all types of tissue on any microtome

6. PLANO CONCAVE KNIFE
• Used primarily for cutting Nitro cellulose embedded tissues
• Available with varying degrees of concavity

7. BICONCAVE KNIFE
• Classical knife shape introduced by Heiffor
• Used with rocking microtome
• Relatively easy to sharpen
• Less rigid, prone to more vibrations
• With gradual adoption of more substantial microtomes, this knife
design has lost popularity.

8. TOOL EDGE(D-PROFILE)
• Tool edge is similar to wood worker’s chisel and hence called “Chisel
edge”
• Used primarily to section exceptionally hard tissue
• Decalcified dense cortical bone, Undecalcified bone
• Stouter than conventional knives to give added rigidity
• Edge may be coated with Tungsten-Carbide for increased life

9. DISPOSABLE BLADE
• Used for routine Microtomy and Cryotomy
• Provide a sharp cutting edge, produce flawless 2 to 4 micron section
• An adaptor or blade holder is incorporated into the microtome
• Blade is coated with PTFE (Poly Tetra FluoroEthylene) which helps in ease of cutting
sections.
• Over tightening the blade in the clamp may cause cutting artifact such as thick and thin
sections.

10. DIAMOND AND GLASS KNIFE
• Used in electron microscopy and with plastic resin embedded blocks

11. KNIFE ANGLES
1. CLEARANCE ANGLE-Angle formed by a line drawn along the block surface and the lower bevel of
the knife
2. RAKE ANGLE-Angle between the upper bevel of the knife and a line at 90 degrees to the block
surface
3. BEVELANGLE-Angle of facets which meet to form the edge
• Vary between 15 and 35 degrees
• Longer facets and smaller bevel would give rise to keener edge.
SHARPNESS OR ACUITY:
Reflection of light by the knife edge when viewed under the microscope.
Figures of 0.3 and 0.1 micrometer necessary for maximal acuity and sharpness

12. KNIFE SHARPENING
Manual/Automatic
1. HONING-Abrasive grinding of the facets
2. STROPPING-Polishing

13. HONING-Abrasive grinding of the knife facet
Naturally occurring slabs of stone with varying abrasive properties
STONES: Belgian black vein and Arkansas, Aloxite and Carborundum-composites.
Lubricated with soapy water or light oil during use.
GLASS PLATES:
• Hand sharpening
• Readily available, cheap
• Surface roughed to enable particles of abrasive to adhere to the glass
• Easily cleaned after use.
COPPER AND BRONZE PLATES:
Used in automatic knife sharpening machines, Expensive with Superior properties

14. ABRASIVES
• Alumina- Aluminium oxide
• Jeweller’s rouge- Iron oxide
• Silicon carbide
• Diamond

15. KNIFE SHARPENING-MANUAL METHOD
• Knife with a ‘back’ effectively raises the non cutting edge up off the hone.
• Back of the knife is ground simultaneously with the edge, hence reserved for use only with
that particular knife
• Hone is placed on the bench on a non-skid surface(damp cloth) to prevent moving during
honing
• Small quantity of light oil or soapy water applied to the hone and smeared over the surface
• Abrasive is applied over the glass or metal plate
• Knife with handle and backing sheath is laid on the hone with cutting edge facing away
from the operator, heel roughly in the center of the nearest end of the hone.

16. KNIFE SHARPENING-MANUAL METHOD
• Handle of the knife is held between the thumb and the forefinger
• Thumb and forefinger of other hand rest on the other end of the knife to ensure
even pressure along the whole edge of the knife
• Knife is pushed forward diagonally from heel to toe turned over on its back and
moved across the hone until the heel is in the center with the cutting edge leading
and then brought back diagonally
• It is then turned over on its back and moved across the hone to its original position
completing figure of eight movement.

17. STROPPING
• Process of polishing an already fairly sharp edge
• Types of Strop: Best strops made from hide from the rump of the horse ‘shell horse’.
• 2 Types : Flexible ( hanging) and rigid.
• Flexible type:
• Back of the strop is made of canvas and is intended to support the leather during stropping.
• Strops should be kept soft by applying a small quantity of vegetable oil into the back of the leather.

18. STROPPING
• Strops should be kept free from grit and dust.
• Rigid type:
• Single leather strop stretched over a wooden frame to give a standard
tension or a block of wood about 12x2x2 inches in size having a
handle at one end with four grades of leather or even a soft stone
cemented on each side.
• The sides of these strops are numbered and the knife is stropped on
No1, then No2 and so on finishing on the finest leather.

19. AUTOMATIC KNIFE SHARPNERS
• Two basic design available.
1) knife is held vertically with revolving sharpening wheels griding the cutting edge.
2) Knife is held horizontally against the surface of a slowly rotating flat plate.
Plates –glass, copper or bronze charged with an abrasive.
Glass plates need to be roughened before use to allow the abrasive partible to be held more easily in
place.
Copper and bronze plates used in conjunction with diamond paste, 6 micrometer particle size being
most appropriate for rough sharpening and 1 micrometer for fine polishing.

20. STROPPING TECHNIQUE
• Knife is laid on the near end of the strop with the cutting edge towards
the operator -opposite direction to that used in honing.
• Knife held with fore finger and thumb to facilitate easy rotation at the
end of each strop.
• Action is exact opposite to that used in honing, using full length of the
strop and stropping evenly the whole of the blade.