Sharpening Glossary
Sharpening Glossary
A
Abrasive - A generic term for the particles, whether naturally occurring mineral or synthetic, on or within a sharpening surface that cut the metal in the sharpening process. Examples of abrasives are: Aluminum Oxide, Chromium Oxide, Cubic Boron Nitride, Diamond, Novaculite, Silicon Carbide, Spessartite, Zirconium Dioxide.
See also: Grit
Acute - 1. having a sharp edge or point.
- 2. having a lower angle as compared to another angle. An edge with a 15 degree cutting angle is more acute than and edge with a 20 degree cutting angle.
- 3. an angle of less than 90 degrees.
See Also: Obtuse.
Alloy - an homogeneous mixture of metallic elements possibly also including one or more non-metallic elements. Alloys have different properties than non-alloyed metals and the proportions of their constituent elements can be varied to achieve desired properties of hardness, corrosion resistance, etc. Steel, brass and bronze are examples of alloys.
Aluminum Oxide - a crystal consisting of two Aluminum and three Oxygen atoms used as an abrasive in sharpening stones, compounds and powders. Also called Alumina or Corundum.
Aluminum Oxide Stone - 1. a sharpening stone made with aluminum oxide as the abrasive.
- 2. a name given to sharpening stones with similar characteristics to India Stones, but which are not made by Saint-Gobain Abrasives, Inc. / Norton Abrasives and therefore can not be called by that trademarked name.
See also: India Stone.
Angle - 1. the shape of an edge formed by the intersection of two bevels.
- 2. the measurement in degrees of the cross section of an edge.
- 3. in knife sharpening, angle often refers to the relation of each individual bevel to the center line of the blade in cross section. In this usage the given angle is usually half of the total angle of the edge of the knife. For example, a knife on which the overall angle of the edge is 30 degrees will often be referred to as having been sharpened to 15 degrees as each bevel is 15 degrees relative to the center line of the knife.
See also: Cutting Angle, Inclusive Angle, Overall Angle, Sharpening Angle.
Arkansas Stone – a natural stone quarried from Ozark novaculite (silicon quartz). Due to their unique crystalline structure, Arkansas Stones polish as they sharpen, imparting a keen smooth edge/surface. Arkansas Stones are divided into different grades based on density as measured by specific gravity. Lower density Arkansas Stones are coarser and higher density ones are finer. In order of least dense/coarsest to most dense/finest the Arkansas Stones are: Washita, Soft Arkansas, Hard Arkansas, Hard Black and Hard Translucent Arkansas.
See also: Soft Arkansas Stone, Hard Arkansas Stone, Hard Black Arkansas Stone, Hard Translucent Arkansas Stone.
B
Belgian Blue Whetstone - a natural stone used for sharpening. Characterized by a high concentration of spessartite garnets, they have a blueish-purple color caused by the presence of iron in the stone. Used with water, these stone form a slurry in use. They are similar to Coticule Whetstones which they are often found near, and sometimes these two stone types occur in adjacent layers naturally joined to one another. Named for the country of Belgium where they are quarried. Their name is often abbreviated as BBW.
See also: Coticule Whetstone, Spessartite, Whetstone.
Bench Stone – an abrasive product in block form used for sharpening knives, tools, etc. Typically used to describe a stone of a size that is convenient to use by placing it on a bench or other work surface as opposed to a stone that would be held in the hand.
See also: Sharpening Stone, Stone, Whetstone.
Bevel – the angle or inclination of a line or surface that meets another at any angle but 90 degrees. One of the surfaces that intersect to form an edge.
Burnisher – a tool, usually with a hard, smooth surface, often round or oval, that is used to turn over a burr on scrapers.
Burr - a ragged protrusion of metal formed on an edge by abrasion or by burnishing. A burr forms on the side of the edge opposite from the side that is against the sharpening or burnishing surface. A burr can be used as an indicator of sharpening progress as its presence indicates a crisp intersection of two bevels. On knives and cutting tools the burr is usually removed as the final step of sharpening. On scrapers, the burr itself performs the cutting action of the tool and is deliberately left in place.
See also: Burnisher
C
CBN - the abbreviated name for cubic boron nitride, a specific crystalline form of boron nitride used as an abrasive consisting of equal numbers of boron and nitrogen atoms and having a hardness second only to diamond. Most often used as an abrasive on grinding wheels meant for sharpening steel at a high speed.
See also: Cubic Boron Nitride.
Camber - an arch or convexity along the length of an edge. Most often used when referring to woodworking hand plane blades.
Carbide - the shortened name for Tungsten Carbide. A compound of the elements tungsten and carbon used to make cutting tools because of its extreme hardness and resistance to high temperatures. Sharpening tungsten carbide cutting tools requires very hard abrasives such as diamond or cubic boron nitride.
Carbon Steel - any steel in which carbon is the main alloying element. In general, higher carbon content makes steel harder. Or any steel that is not stainless steel.
Carborundum - a trademarked name for any of several man made crystalline substances used as abrasives, especially ones involving silicon carbide. The trademark is currently held by Saint-Gobain Abrasives, Inc. the parent company of Norton Abrasives.
See also: Carborundum Stone, Silicon Carbide
Carborundum Stone - a trademarked name for a stone made with Carborundum as an abrasive.
See also: Carborundum, Crystolon Stone, Silicon Carbide Stone
Ceramic Knife - a knife with a blade made from a ceramic material, often zirconium dioxide, instead of the more usual steel. Ceramic blades are very hard and hold an edge very well, often better than steel. However, they are difficult to sharpen, usually requiring the use of diamond abrasives.
Ceramic Stone - also called Ceramic Honing Stone or Ceramic Sharpening Stone. A stone manufactured as a fused block or rod of ceramic material. Ceramic Stones are very hard wearing and usually used dry, without oil or water as a cutting fluid. Available in medium, fine and ultra fine stones that correspond to roughly 600, 1200 and 2000 grits respectively. Ceramic Stones are not the same as and should not be confused with Ceramic Water Stones.
Ceramic Water Stone - a specific type of Water Stone, a Ceramic Water Stone is a composite ceramic product in which individual pieces of ceramic abrasive material are held together with a resin binder. They are used with water as a cutting fluid like other water stones, however they are harder wearing than other water stones and do not require soaking prior to use. Available from 122.5 micron/120 grit through .49 micron/30,000 grit. Ceramic Water Stones are not the same as and should not be confused with Ceramic Stones.
Chromium Oxide - an inorganic compound consisting of 2 chromium and 3 oxygen atoms which forms hard crystals and is often used as an abrasive. Chromium oxide is green in color and is also often used as a pigment. Honing compounds made with it are often referred to by names such as green honing paste or green rouge. It is one of the grits in our Green Honing Compound.
Concave - a surface or line that is curved like the interior of a circle or that is lower in the middle than at its edges or ends. The top side of a spoon is concave. Usually refers to a bevel that is concave in cross section, typically from having been created on a grinding wheel. Can also refer to an edge that has a concave curve along its length.
See also: Concave Grind, Hollow Grind
Concave Grind - a bevel that has been shaped such that it is concave in cross section as opposed to flat or convex. A Concave Grind is usually created using a grinding wheel.
See also: Convex Grind, Flat Grind, Hollow Grind.
Continuous Surface - referring to a a diamond sharpening stone on which the diamonds evenly cover the entire surface without voids or interruptions. Useful for small or finely pointed tools that can catch in the voids of an interrupted surface.
Convex - a surface or line that is curved like the exterior of a circle or that is higher in the middle than at its edges or ends. The back side of a spoon is convex. Usually refers to a bevel that is convex in cross section. Can also refer to an edge that has a convex curve along its length.
See also: Concave, Concave Grind, Hollow Grind
Convex Grind - a bevel that has been shaped such that it is convex in cross section as opposed to flat or concave. A Convex Grind is usually created using a belt grinder.
See also: Concave Grind, Flat Grind, Hollow Grind.
Coticule Whetstone - a natural stone used for sharpening. Characterized by a high concentration of spessartite garnets, they have a characteristic white-yellow color. Somewhat brittle, they are often affixed to a separate piece of slate as a backing stone to prevent breakage. The slate is intended for structure only and is not used in the sharpening process. Used with water for sharpening, they form a slurry in use. Quarried in the country of Belgium, they often occur near Belgian Blue Whetstones and sometimes these two stone types occur in adjacent layers naturally joined to one another.
See also: Belgian Blue Whetstone, Spessartite, Whetstone.
Crystolon Stone - a trademarked name for certain sharpening stones manufactured by Saint-Gobain, Inc / Norton Abrasives. Crystolon Stones are oil stones typically made with silicon carbide abrasives, and are known for being fast cutting. They are the fastest cutting oil stones we carry. Crystolon stones are softer and faster wearing than India Stones. Gray in color. Available in coarse 120 grit, medium 180 grit, and fine 320 grit.
See also: India Stone.
Cubic Boron Nitride - a specific crystalline form of boron nitride used as an abrasive consisting of equal numbers of boron and nitrogen atoms and having a hardness second only to diamond. Most often used as an abrasive on grinding wheels meant for sharpening steel at a high speed. Sometimes abbreviated as CBN.
See also: CBN
Cutting Angle - The angle of the intersection of the bevels that make an edge, measured in degrees. The term cutting angle is used to differentiate the overall angle from the sharpening angle in cases where the sharpening angle is given as the relation of each bevel to the center line of the blade. In such cases, the cutting angle is the sum of the sharpening angles. This situation is most often found in knife sharpening. Sometimes called the inclusive angle.
See also: Angle, Inclusive Angle, Overall Angle, Sharpening Angle.
Cutting Fluid - a fluid used in sharpening to float away swarf in order to avoid clogging the sharpening stone. Usually water or oil.
D
Damascus Steel - originally referred to a steel made in various Asian countries circa 700 - 1000 that was renowned for its excellent flexibility and edge retention. Damascus steel had a distinctive wave or water like pattern of lines left visible after forging. In contemporary usage, Damascus Steel refers to any steel that is pattern forged so that a visible pattern of lines forms in the body of the steel, and does not have any correlation with the qualities of hardness or flexibility of the steel.
Diamond - a crystalline form of pure carbon used as an abrasive. The hardest of known minerals. Used in sharpening stones and grinding wheels when durability and the ability to cut very hard metals are important factors. The primary abrasive used for sharpening carbide.
Diamond Stone - most commonly a stone containing a single layer of small diamonds attached to the face of a metal plate or sometimes a stone with a thicker layer of diamonds held in a wearable binder. Used for sharpening knives, tools, etc. The two greatest advantages of the diamond stone are the very fast cutting that the diamonds provide, and in the case of the stones made of diamonds mounted to a metal plate, the flatness that is retained with use by the diamond stone.
See also: Continuous Surface, Interrupted Surface.
E
Edge - the line of intersection of two surfaces. A highly sharpened edge is one where the two surfaces are highly polished to form a very fine intersection.
F
Flat Grind - a bevel that is flat in cross section, as opposed to convex or concave.
See also: Concave Grind, Convex Grind, Hollow Grind.
Flattening Stone - an abrasive plate or stone used to flatten or resurface a sharpening stone.
See also: Lapping Plate, Lapping Stone.
Fleam - 1. the leading edge of a saw tooth.
- 2. an archaic surgical tool used for drawing blood.
G
Grind - 1. to remove material or sharpen by abrasion, particularly as done with an abrasive wheel.
- 2. the cross sectional shape of one or more of the bevels that create an edge. For example, flat grind, convex grind, concave grind.
See Also: Concave Grind, Flat Grind, Hollow Grind.
Grinding Wheel - any of many varieties of sharpening stone in the form of an abrasive wheel or disk that spins on an arbor.
Grit - 1. a generic term for the abrasive particles used in sharpening. Examples of grit are: Aluminum Oxide, Chromium Oxide, Cubic Boron Nitride, Diamond, Novaculite, Silicon Carbide, Spessartite, Zirconium Dioxide.
- 2. the numeric term used to describe the number of openings per linear unit in a screen used to sort particles; a measurement of abrasive grains. Low grit numbers are coarser and high grit numbers are finer.
See also: Abrasive, Mesh.
H
Hard Arkansas Stone - an Arkansas Stone with a specific gravity of 2.30 - 2.45. Denser and finer than Washita Stones and Soft Arkansas Stones, but less dense and coarser than Hard Black Arkansas or Hard Translucent Arkansas stones, Hard Arkansas Stones are comparable to 800 - 1000 grit. They may be gray, white, pink or black or any combination of those colors. Color is not considered in grading, only specific gravity.
See also: Arkansas Stone, Soft Arkansas Stone, Hard Black Arkansas Stone, Hard Translucent Arkansas Stone.
Hard Black Arkansas Stone - an Arkansas Stone with a specific gravity of 2.5 or higher, and which is black in color. Denser and finer than Washita Stones, Soft Arkansas Stones, and Hard Arkansas Stones, but similar in density and fineness to Hard Translucent Arkansas Stones. Hard Black Arkansas Stones are comparable to 1200 + grit. Color is considered in selecting Hard Black Arkansas Stones stones.
See also: Arkansas Stone, Soft Arkansas Stone, Hard Arkansas Stone.
Hard Translucent Arkansas Stone - an Arkansas Stone with a specific gravity of 2.5 or higher, which is white or gray in color, possibly including streaks of other colors, and which allows some light to pass through it. Denser and finer than Washita Stones, Soft Arkansas Stones, and Hard Arkansas Stones, but similar in density and fineness to Hard Black Arkansas Stones. Hard Translucent Arkansas Stones are comparable to 1200 + grit. Color is considered in selecting Hard Translucent Arkansas Stones stones.
See also: Arkansas Stone, Soft Arkansas Stone, Hard Arkansas Stone, Hard Black Arkansas Stone.
High-Speed Steel - any of several types of tool steel formulated to retain their hardness at high temperatures. Cutting tools made of high-speed steel are used in environments of high heat or friction such as lathe turning. Sometimes abbreviated as HSS.
Hollow Grind - 1. a bevel that has been shaped on a grinding wheel such that it is concave in cross section as opposed to flat or convex.
- 2. to create such a bevel.
See also: Concave Grind, Flat Grind.
Hone - 1. a fine-grained whetstone for giving a keen edge to a cutting tool.
- 2. to sharpen on a fine-grained whetstone.
- 3. occasionally used to refer to the process of sharpening.
Honing Compound - fine abrasive either in powder form or mixed in a medium such as wax to make a bar or paste. Used for polishing an edge. Honing Compounds are usually used with a strop.
See also: Honing Paste, Honing Powder.
Honing Paste - fine abrasive mixed in a medium such as wax to make a paste. Used for polishing an edge. Honing Pastes are often used with a strop.
See also: Honing Compound, Honing Powder.
Honing Powder - fine abrasive in powder form. Used for polishing an edge. Honing Powder is often used with a strop.
See also: Honing Compound, Honing Paste.
Honing Guide - a jig used to hold a tool or knife steady during sharpening, increasing efficiency by ensuring a consistent bevel angle.
See also: Sharpening Guide, Tool Sharpening Guide.
Honing Oil - a non-hardening liquid, usually mineral oil, used as a cutting fluid when sharpening with oil stones.
I
Inclusive Angle - The angle of the intersection of the bevels that make an edge, measured in degrees. The term inclusive angle is used to differentiate the overall angle from the sharpening angle in cases where the sharpening angle is given as the relation of each bevel to the center line of the blade. In such cases, the inclusive angle is the sum of the sharpening angles. This situation is most often found in knife sharpening. Sometimes called the cutting angle.
See also: Angle, Cutting Angle, Overall Angle, Sharpening Angle.
India Stone – a trademarked name for certain stones manufactured by Saint-Gobain Abrasives, Inc / Norton Abrasives. India Stones are oil stones made with aluminum oxide abrasive and are harder and slower wearing than Crystolon Stones, but are also slower cutting. Orange/brown in color. Available in coarse 150 grit, medium 240grit and fine 400 grit.
See also: Crystolon Stone.
Interrupted Surface - referring to a diamond sharpening stone on which the diamond covered surface features periodic voids which trap metal debris during sharpening. This trapping of debris prevents clogging of the diamond grit and speeds sharpening.
Iron - 1. A ductile, malleable metallic element used as a base in alloys to create steel used for making cutting tools.
- 2. the cutting blade of a woodworking hand plane.
See also: Plane Iron.
K
Keen - finely sharpened.
L
Lapping Plate - an abrasive plate or stone used to flatten or resurface a sharpening stone.
See also: Flattening Stone, Lapping Stone.
Lapping Stone - an abrasive plate or stone used to flatten or resurface a sharpening stone.
See also: Flattening Stone, Lapping Plate.
M
Mesh - the numeric term used to describe the number of openings per linear unit in a screen used to sort particles; a measurement of abrasive grains. Low mesh numbers are coarser and high mesh numbers are finer.
See Also: Grit.
Micron - one millionth of a meter or one thousandth of a millimeter. Sometimes used to measure abrasive particles. The higher the micron number, the coarser the abrasive and the lower the micron number the finer the abrasive. Abbreviated as μm
N
Nagura - the Japanese word for any stone which is applied to any other sharpening stone for the purpose of creating an abrasive slurry or for cleaning the surface of that sharpening stone
Novaculite - a fine grained sedimentary rock containing microcrystalline quartz. Arkansas Stones are made of Novaculite.
O
Obtuse - 1. having an edge that is not pointed, blunt.
- 2. having an angle that is higher as compared to another angle. An edge with a 20 degree cutting angle is more obtuse than an edge with a 15 degree cutting angle.
- 3. having an angle more than 90 degrees.
See Also: Acute.
Oil Stone - a stone made of one of three following materials: novaculite, aluminum oxide, or silicon carbide which uses oil as a means to remove the swarf. Arkansas Stones, Crystolon Stones and India Stones are all Oil Stones. The good overall performance and the modest price are the oil stone’s greatest assets.
Overall Angle - The angle of the intersection of the bevels that make an edge, measured in degrees. The term overall angle is used to differentiate the total angle from the sharpening angle in cases where the sharpening angle is given as the relation of each bevel to the center line of the blade. In such cases, the inclusive angle is the sum of the sharpening angles. This situation is most often found in knife sharpening. Sometimes called the cutting angle or inclusive angle.
See also: Angle, Cutting Angle, Inclusivel Angle, Sharpening Angle.
P
Plane Iron - the cutting blade of a woodworking hand plane.
See also: Iron.
Polish - 1. to make smooth and glossy by friction.
- 2. to sharpen using very fine grit abrasive after coarser abrasives have been used to create an edge.
R
Razor Strop - a type of strop consisting of a belt or strap of leather or fabric used by anchoring one end to a fixed point and grasping the other by hand to pull the belt taut. Razor Strops may be used with or without honing compound applied to their surface. The name Razor Strop reflects this type of strop's close association with preparing straight razors for shaving.
See Also: Strop.
Rockwell Scale - a scale used to measure the relative hardness of materials based on the penetration depth of a specific type of indenting tool applied under a standard load. Various Rockwell scales are used for different materials, and each scale has a different letter designation. The C scale is used for steels and is indicated as Rockwell C or HRC followed by a number. The higher the number, the harder the steel. Rockwell values for knives and woodworking tools are typically in the 50's - mid 60's.
S
Serrated - having a notched edge or sawlike teeth.
Sharpening - the process of removing material to create a cutting edge.
Sharpening Angle - 1. the degree of inclination at which a tool is held relative to the sharpening stone.
- 2. the angle to which an edge is sharpened.
- 3. in knife sharpening, the degree of inclination at which the knife is held to the sharpening stone relative to the center line of the knife. Usually half of the overall angle of the edge. For example, a knife with an overall edge angle of 30 degrees is said to have a sharpening angle of 15 degrees.
See Also: Angle, Cutting Angle.
Sharpening Guide - a jig used to hold a tool or knife steady during sharpening, increasing efficiency by ensuring a consistent bevel angle.
See also: Honing Guide, Tool Sharpening Guide.
Sharpening Stone - an abrasive product in block form used for sharpening knives, tools, etc.
See Also: Bench Stone, Stone, Water Stone, Whetstone.
Silicon Carbide - an extremely hard blue/black crystalline substance consisting of one Silicon atom and one Carbon atom. Used as an abrasive in sharpening stones, powders and compounds.
See Also: Carborundum.
Silicon Carbide Stone - a stone manufactured with Silicon Carbide Abrasive.
See Also: Carborundum Stone, Crystolon Stone.
Sink Bridge - a stone holder designed to fit over a sink. Sink Bridges are particularly useful with water stones as sharpening over a sink provides close access to a water source and facilitates mess containment and clean up.
Slip Stone - a sharpening stone with rounded or tapered edges. Use for sharpening knives or tools with heavily shaped edges, especially carving gouges and v tools.
Soft Arkansas Stone - an Arkansas Stone with a specific gravity of 2.25 - 2.30. Denser and finer than Washita Stones, but less dense and coarser than Hard Arkansas, Hard Black Arkansas or Hard Translucent Arkansas stones, Soft Arkansas Stones are comparable to 600-800 grit. They may be gray, white, pink or black or any combination of those colors. Color is not considered in grading, only specific gravity.
See also: Arkansas Stone, Hard Arkansas Stone, Hard Black Arkansas Stone, Hard Translucent Arkansas Stone.
Specific Gravity - The ratio of the density of a material compared to the density of water.
Spessartite - A form of garnet composed of manganese aluminum silicate and named for a region of Bavaria where it is found. It is the abrasive mineral in Belgian Blue Whetstones and Coticule Whetstones. AKA Spessertine.
See also: Belgian Blue Whetstone, Coticule Whetstone.
Stainless Steel - any of several steel alloys that are resistant to corrosion due to the relatively large amounts of chromium they contain. Used to make cutting blades when rust resistance is important, such as with kitchen knives.
Steel - 1. the iron alloy most commonly used to make edged cutting tools.
- 2. originally referred to a metal rod designed for sharpening or realigning the edge of knives. The rod can have file-like grooves on its surface or it may be smooth. In contemporary usage, steel also is used to describe any rod shaped sharpening device with a handle. For instance, there are diamond and ceramic steels.
- 3. to sharpen using a sharpening steel.
Stone - 1. A small piece of rock like a pebble.
- 2. an abrasive product in block form used for sharpening knives, tools, etc.
See also: Bench Stone, Sharpening Stone, Water Stone, Whetstone.
Strop – 1. any of several devices used for sharpening, especially for polishing to a high degree of sharpness. Strops often consist of a piece of leather or cloth, which may be attached to a solid base like a piece of wood or left unmounted as a hanging belt or strap, but can also be made of uncovered wood or sometimes of synthetic material. Strops are sometimes shaped to specific shapes or contours to fit particular tools such as carving gouges. Strops are often used with honing compounds applied to their surface but can be used plain.
- 2. to use such a device to sharpen.
See Also: Razor Strop.
Super Steel - Any of several varieties of steel that exhibit good edge retention. Typically applied to steel with high abrasion resistance or hardness. There is not a universally accepted definition of what constitutes a super steel, and manufacturers, knife sellers, and users apply the term at will. Blades labeled as being made of super steel may be more difficult to sharpen because of their high abrasion resistance.
Surgical Steel - Any of several grades of stainless steel commonly used for the manufacture of medical implements. There is not a universally accepted definition of what constitutes a surgical steel, and manufacturers apply the term at will.
See also: Stainless Steel, Steel.
Swarf – fine metal filings or shavings removed by a cutting tool, sharpening stone, or abrasive.
T
Temper - 1. to give a desired hardness to steel through a process of controlled heating and cooling.
- 2. the particular hardness imparted to steel through this process. Excessive heat created during the sharpening process can reduce this hardness.
Tool Sharpening Guide - a jig used to hold a tool or knife steady during sharpening, increasing efficiency by ensuring a consistent bevel angle.
See also: Honing Guide, Sharpening Guide.
Tool Steel - any of several varieties of steel that are used for making tools because their properties of hardness, abrasion resistance and edge retention make them particularly suited to that purpose.
Tungsten Carbide - a compound of tungsten and carbon used to make cutting tools because of its extreme hardness and resistance to high temperatures. Sharpening tungsten carbide cutting tools requires very hard abrasives such as diamond or cubic boron nitride. Sometimes referred to in the shortened form of Carbide.
W
Water Stone – an abrasive stone, available in both natural and synthetic material, used to sharpen knives and tools with water as a means to remove the swarf. Fast cutting stones, water stones tend to wear unevenly which necessitates periodic flattening. Available in grits from 122.5 micron/120 mesh to .49 micron/30,000 mesh.
Whet - to sharpen by abrading or grinding. Now a somewhat archaic word.
Whetstone – an abrasive product in block form used for sharpening knives, tools, etc. Often confused with Water Stone because of the phonetic similarity between "wet" - soaked with water, and "whet" - to sharpen. All sharpening stones are whetstones. Only some whetstones are water stones.
See also: Bench Stone, Sharpening Stone, Stone
Z
Zirconium Dioxide - a crystalline material consisting of one zirconium and two oxygen atoms also known as zirconia or zirconium oxide. A very hard ceramic material, zirconium dioxide is used for making ceramic knife blades. Zirconia is also used as an abrasive material in heavy-duty sanding belts.