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Chapter-
Material Science: The discipline of investigating the relationships that exist between the structures
and properties of materials. Thus Material Science is the branch of applied science dealing aforesaid
properties of solid engineering materials. Whereas material engineering is the discipline of
designing or engineering the structure of a material to produce a predetermined set of properties
based on established structure-property correlation
Four Major Components of Material Science and Engineering: Structure of Materials
Properties of Materials
Processing of Materials
Performance of Materials
Scope of Civil Engineering Material Civil Engineering material is primarily concerned with the development of new or improved Civil
Engineering structures such as buildings, bridges, roads, sewers, dams, airports. It can be used to
repair existing structures that may be damaged due to, for example, attack by our aggressive
environment, structural overload, earthquakes, storms, etc. The scope of civil engineering material
is based on the field of civil engineering.
Types of Engineering Materials Engineering Materials can be classified as following: A. Civil Engineering Materials
Examples: Building Stones, Bricks and clay product, cementing materials: Lime and Cement Concrete, Mortar, Timber B. Electrical Engineering Materials:
Examples: Copper, aluminum, iron and steel etc. -------- Conductors : Asbestos (A fibrous amphibole; used for making fireproof articles), Bakelite (type of plastic), mica, varnishes, and air etc. -------------- Insulator : Iron, Nickel, cobalt, etc. ------ Magnetic materials. C. Mechanical Engineering Materials:
Examples: Cast iron, steel, lubricating materials etc. Other types of Construction Materials are: 1.0 Metals : It may be further divided as:
Ferrous Metals: Metals containing iron are called Ferrous Metals.
Examples: cast iron, wrought iron and steel. Non-ferrous Metals: Metals not containing iron are called as Non-ferrous metals, Examples: Copper, aluminium, zinc etc.
2.0 Non-metals: Building stones, cement, concrete, rubber, plastic, Asbestos etc.
3.0 Alloys: Product of more than one element is known as Alloys. Steel is an alloy of iron and carbon.
Ferrous Alloys: Product of metal and any other element is called ferrous alloy, Examples: silicon steel, high speed steel, spring steel etc. Non-ferrous Alloy: Product of non-ferrous metal and other element is called non-ferrous alloy. Examples: brass, bronze, duralumin etc. 4.0 Timber: Timber is another name for wood, whether still standing in the form of trees or felled and turned into boards for construction. Some people may also refer to timber as lumber, or differentiate between timber as unprocessed wood and lumber as cut wood packaged for commercial sale. The timber industry around the world is huge, providing wood for a variety of products from paper to particleboard.
Uses: Cladding, Boards, Column, Beams 5.0 Ceramics Materials: Ceramics Materials: A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous (e.g., a glass). The essential engineering properties of ceramics are that they have an ability to withstand high temperatures and retain their high strength and rigidity. Ceramics also offer electrical and insulating properties.Ceramics are phases, inorganic non metallic materials fabricated by shaping the powder with or without pressure into a compact, subjected to temperature treatment (sintering). Example: silica, soda lime glass, concrete cement, ferrites (i.e. solid solution), garnets (i.e. mineral), MgO, CdS, ZnO, SiC, etc
6.0 Polymers: A polymer is a chemical compound or mixture of compounds consisting of repeating structural units created through a process of polymerization. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. The list of synthetic polymers includes synthetic rubber, PVC.
(f) Porosity: The degree by which the volume of material is occupied by pores is indicated by the term porosity. The strength, bulk density, durability, thermal con-ductility etc. of a material depends on it‘s porosity.
(g) Water absorption: It is the ability of material to absorb and retain the water. It mainly depends on the volume, size and shape of pores present in the material.
(h) Water Permeability: It is the capacity of material to permit water to pass through it under pressure.
(i) Fire resistance: It is the ability to resist the action of high temperature without losing it‘s load bearing capacity.
(j) Durability: It is the property of material to resist the combined action of atmospheric and other factors.
(k) Refractoriness: It is the ability of a material to withstand prolonged action of high temperature without melting or loosing shape.
2. Mechanical Properties: Mechanical properties of engineering materials are such properties, which defines the behavior of materials under the action of load or force. The study of mechanical properties is very important in order to select the material for various engineering requirements. It consist followings:
(a) Strength: If a metal can withstand higher stresses before it‘s fracture under the action of loading, it gives it‘s strength.
i. Compressive Strength: Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. It provides data (or a plot) of force vs deformation for the conditions of the test method. When the limit of compressive strength is reached, brittle materials are crushed. Concrete can be made to have high compressive strength, e.g. many concrete structures have compressive strengths in excess of 50 MPa, whereas a material such as soft sandstone may have a compressive strength as low as 5 or 10 MPa. By contrast, a small plastic container might have a compressive strength of less than 250 N.
ii. Tensile Strength: Tensile strength is the capacity of a material or structure to withstand axially directed pulling forces. It provides data (or a plot) of force vs deformation for the conditions of the test method. When the limit of tensile strength is reached, ductile materials are fractured.
Material Comppressive Strength (kPa)
Tensile Strength (kPa)
Bricks, hard 80000 2800 Bricks, light 7000 280 Brickwork, common quality
Brickwork, best quality 14000 2100 Limestone 60000 2100 Portland Cement, less than one month old
Portland Cement, more than one year old
Portland Concrete 7000 1400 Portland Concrete, more 14000 2800
discontinuous chips indicates that metal is brittle. Materials which withstand high compressive strength are called brittle. Concrete, Asbestos, glass, cast iron are the example of brittle materials.
(g) Hardness: It is defined as an ability of metal by virtue of which the metal gives resistance to cutting, bending, drilling, abrasion etc. by harder bodies then this ability is known as it‘s hardness. If the metal is very hard it‘s corresponding melting point and bond strength is also higher.
(h) Stiffness: It is defined as the property of metal by virtue of which a metal gives resistance to deformation (deflection) then we can say the metal is stiff. Under the application of load, if a metal deflects with a low angle of deflection, then it‘s corresponding stiffness is higher and vice versa.
(i) Creep: Creep is the tendency of a solid material to move slowly or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and near melting point. Creep always increases with temperature. The rate of this deformation is a function of the material properties, exposure time, exposure temperature and the applied structural load. For example creep of a turbine blade will cause the blade to contact the casing, resulting in the failure of the blade. Above 0.4 Tm (melting temperature) plastic deformation in metal takes place. This deformation is a function of time with the application of steady load. This Phenomenon is called creep. In short, it can be remembered as LTTE. Where, L = Load, T = temperature (constant parameters), T = Time, E = Elongation (variables). (j) Fatigue (Endurance): Fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. Fatigue occurs when a material is subjected to repeat loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators. Eventually a crack will reach a critical size, and the structure will suddenly fracture. Toughness: It is defined as an ability of metal by virtue of which how much energy it can sustain (observe) before its fracture under the action of loading. If a metal has high toughness then its corresponding impact strength is also higher, vice versa. It has already been understood that steel is tougher than cast iron. In Other word, ductile metals are having more toughness as compare with brittle materials
(k) Abrasion Resistance: Abrasion resistance is a property which allows a material to resist wear and tear. Numerous companies manufacture abrasion resistant products for a variety of applications, including products which can be custom fabricated to meet the needs of specific users. When a product has abrasion resistance, it will resist erosion caused by scraping, rubbing, and other types of mechanical wear. This allows the material to retain its integrity and hold its form.
(l) Resilience: Resilience is the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without creating a permanent distortion. Proof Resilience: The maximum amount of energy that can be stored within elastic limit of the metal is called it‘s proof resilience. Modulus of resilience. Proof resilience per unit volume of material defines modulus of resilience.
3. Thermal Properties: It consist followings:
(a) Specific heat: The specific heat of the substance is defined as the amount of heat required to raise the temperature of unit mass of substance through 1oC.
Q= m×s× (θ 2 - θ 1 ) where ―Q‖ is amount of heat, ―m‖ is mass of
substance and ―s‖ is specific heat. Substance Specific Heat (J/kgoC) Sandy clay 1381 Quartz sand 830 Water, pure 4186 Wet mud 2512 Wood
conduction should be kept to a minimum. Silver is the best conductor and copper is next. Material Thermal Conductivity (W/m K) Diamond 1000 Aluminum 205. Iron 79. Steel 50. Concrete 0. Wood 0.12-0.
(c) Thermal Expansion in solids: - The thermal expansion takes place in all bodies and in all three states in matter i.e. solid, liquid and gas. Linear coefficient of expansion : The linear coefficient of expansion of a solid is defined as the increase in length per unit length, for each degree rise in temperature. Superficial coefficient of expansion : The Superficial coefficient of expansion of a solid is defined as the increase in are per unit area, for each degree rise in temperature. Cubical coefficient of expansion : The Cubical coefficient of expansion of a solid is defined as the increase in volume per unit volume, for each degree rise in temperature. (d) Thermal resistivity: It is defined as the property of material in which the resistance to flow the heat. It is the reciprocal of thermal conductivity.
4. Electrical Properties: It comprises:
a. Conductivity: Electrical conductivity is a measure of how well a material accommodates the movement of an electric charge. It is the ratio of the current density and the electric field strength. Electrical conductivity or specific conductance is the reciprocal quantity, and measures a material's ability to conduct an electric current.
b. Electrical Permittivity: A measure of the ability of a material to resist the formation of an electric field within it. When the charges are located in some other medium rather than vaccum then the force between the charges will be Where ɛ is the absolute electric permittivity of the medium. The force between the charges held at same distance from each other in vaccum is Whereɛr is the relative electrical permittivity.
Chapter- Two/ Clay Products
CLAY: Clay is a naturally occurring aluminium silicate composed primarily of fine-grained minerals. Clay deposits are mostly composed of clay minerals, a subtype of phyllosilicate minerals, which impart plasticity and harden when fired or dried; they also may contain variable amounts of water trapped in the mineral structure by polar attraction. Organic materials which do not impart plasticity may also be a part of clay deposits. Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lakes and marine deposits. Clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts,
which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than
clays, but there is some overlap in both particle size and other physical properties, and there are
many naturally occurring deposits which include both silts and clays. The distinction between silt
and clay varies by discipline. Geologists and soil scientists usually consider the separation to occur
at a particle size of 2 μm (clays being finer than silts), sedimentologists often use 4-5 μm, and
colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the
plasticity properties of the soil, as measured by the soils' Atterberg Limits. ISO 14688 grades clay
particles as being smaller than 2 μm and silts larger.
Clay possesses following properties: Clay possesses plasticity when moist. Clay possesses rigidity when dried. Clay possesses strength and hardness when fired.
Classification of Clay:
1. Residual Clay: - Formed directly from rock by direct process and pure in chemical composition that is related to the parent rock. 2. Transported clay: - Formed by disintegration and decomposition of the pre-existing rocks by natural agencies followed by removal and transport of broken pieces.
Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, dishware, and even musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is also used in many industrial processes, such as paper making, cement production, and chemical filtering. Clay is also often used in the manufacture of pipes for smoking tobacco. Until the late 20th century bentonite clay was widely used as a mold binder in the manufacture of sand castings. Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage (lining the landfill, preferably in combination with geo-textiles). CONSTITUENTS OF GOOD EARTH BRICK
1. Alumina: It is the chief constituent of every kind of clay. A good brick earth should contain about 20% to 30% of alumina. This constituent imparts plasticity to the earth so that it can be moulded. If alumina is present in excess, with inadequate quantity of sand, the raw bricks shrink and warp during drying and burning and become too hard when burnt. 2. Silica or Sand: It exists in clay either as free or combined. As free sand, it is mechanically mixed with clay and in combined form; it exists in chemical composition with alumina. A good brick earth should contain about 50% to 60% of silica. The presence of this constituent prevents cracking, shrinking and warping of raw bricks. It imparts uniform shape to the bricks. The durability of bricks depends on the proper proportion of silica in brick earth. The excess of silica destroys the cohesion between particles and the bricks become brittle. 3. Lime: A small quantity of lime not exceeding 5 % is desirable in good brick earth. It should be present in a very finely powered state because even small particles of the size of a pin head cause flaking (cracking) on the bricks. The lime prevents shrinkage of raw bricks. The sand alone is infusible. But it slightly fuses at kiln temperature in presence if lime. Such fused sand works as a hard cementing material for brick particles. The excess of lime causes the brick to melt and hence it shape is lost. The lumps of lime are converted into quick lime after burning and this quick lime slakes and expands in presence of moisture. Such an action results in splitting of bricks into pieces. It acts as a flux. 4. Oxide of iron: A small quantity of oxide of iron to the extent of about 5 to 6 percent is desirable in good brick earth. It helps as lime to defuse sand. It also imparts red color to the bricks. The excess of oxide of iron makes the bricks dark blue or blackish. If, on the other hand, the quantity of iron oxide is comparatively less , the bricks will be yellowish in color. 5. Magnesia: A small quantity of magnesia in brick earth imparts yellow tint to the bricks and decreases shrinkage. But excess of magnesia leads to the decay of bricks.
Bricks:
Building bricks may be defined as structural units of rectangular shape and convenient size that are made from suitable types of clays by different processes s involving moulding, drying, burning. A good brick earth should have following compositions: Alumina or clay : 20 to 30% by weight Silica or Sand : 35 to 50% by weight Silt : 20 to 25% by weight
vi. Drying of bricks: It is done to make brick strong, to allow loss of moisture and to save fuel during burning stage.
Air Dry: 4-10 days, 2-4% moisture remained.
Sun Dried: Dried directly from sunlight. Takes 25 days to dry.
Artificial drying: Chamber drying and Tunnel Drying-2-4 Days.
vii. Burning of bricks: Dehydration-425-765°C, Oxidation-900°C and vitrification-900-1100°C- softening of Alumina and silica by fluxing agents.( Clamps and Brick Kiln are used)-Loading, Preheating, Burning, Cooling, Unloading are the process of burning bricks. After 8 weeks ready for use.
Qualities of good bricks
Well burnt bricks are copper colored and are free from cracks. They posses sharp and square edges. They are of uniform color, shape and size as per standard. When struck with each other, they produce clear metallic ringing sound. Fracture of good bricks show uniform and bright compact structure without any voids. They absorb minimum water when immersed in water. The absorption should not be more than 20 % when immersed in water for 24 hours. Good bricks are hard on their surface and leave no impression when scratched with nails. Good bricks do not break when dropped from 1 m height. Good bricks when soaked in water and dried, do not show white patches or white deposits on their surface The good quality bricks could be gauged easily by the percentage of bricks that get broken in transit and stacking in the course of ordinary handling (2 to 3%).
Classification of Brick:
1. First Class Brick: This type of brick has well burnt having even surface and perfectly rectangular shape. When two bricks are struck against each other a ringing sound is produced. The compressive strength shall not be less than 140 kg/cm 2 and its absorption after 24 hrs shall not exceed 20 %. It should show a uniform appearance. Texture and structure when seen on fracturing. It can be used for
II:
Compressive Strength: 70 Kg/cm Water Absorption: 20% Efflorescence: Very Little Tolerance in Dimension: ± 8% Shape and Other Properties: Slight deformation in shape LI: Compressive Strength: 35 Kg/cm Water Absorption: 25% Efflorescence: Very Little Tolerance in Dimension: ± 3% Shape and Other Properties: No metallic sound, smooth, rectangular, sharp edge LII: Compressive Strength: 35 Kg/cm Water Absorption: 25% Efflorescence: Very Little Tolerance in Dimension: ± 8% Shape and Other Properties: Slight deformation in shape
Properties of Bricks:
1. Physical Properties:
a. Shape: The standard shape of an ideal brick is truly rectangular. It has well defined and sharp edges and corners. The surface of the bricks is regular and even. Special purpose bricks may, however, be either cut or manufactured in various other
b. Size: The size of the brick used in construction varies from country to country and from place to place in the same country. The basic standard size used in Nepal is 23× 13× 5.5 cm but in India the ideal size of brick 19× 9× 9 cm with which mortar joint gives net dimension of 20× 10× 10 cm.
c. Colour: The most common colour of building bricks fall under the class RED. It may vary from deep red to light red to buff and purple. A very dark shade of red indicates over burning whereas yellow colour indicates under burning.
d. Density: The density of bricks or weight per unit volume depends mostly on the type of clay used and method of brick moulding. In the case of standard bricks, density varies from 1600 kg/cubic meter to 1900 kg/cubic meter. A single brick (19× 9× 9 cm) will weigh between 3.2 to 3.5 kg.
2. Mechanical Properties:
a. Compressive Strength: It is the most important property of bricks especially because they are to be used in load bearing walls. The compressive strength of a brick depends on the composition of clay and degree of burning. It may vary from 35 kg/cm 2 to 200 kg/cm 2.
b. Flexure Strength: Bricks are often used in situations where bending loads are likely to develop in building. As such, bricks used in such places should possess sufficient strength against transverse loads. Flexure strength of bricks shall not be less that 10 kg/cm2. The best graded brick should have the flexure strength of 20 kg/cm 2.
3. Thermal Characteristics: Besides being hard and strong, an ideal brick should also provide adequate insulation against heat, cold and noise. The heat and sound conductivity of bricks varies greatly with their density and porosity. Very dense and heavy bricks conduct heat and sound at greater rate. They have poor thermal and acoustic insulation qualities.
4. Durability: By durability of bricks it is understood the length of time for which they remain
unaltered and strong when used in construction. Experience has shown that properly manufactured bricks are among the most durable of man-made materials of construction. The durability of bricks depends upon absorption value, frost resistance and efflorescence.
TESTS ON BRICKS
1. Shape and Size Test: (I) Uniformity in Size: A good brick should have rectangular plane surface and uniform in size. This check is made in the field by observation.
(II) Uniformity in shape: A good brick will be having uniform shape throughout. This observation may be made before purchasing the brick. To check it, 20 bricks are selected at random and they are stacked along the length, along the width
and then along the height. For the standard bricks of size 190 mm × 90 mm ×90mm IS code permits
the following limits: Lengthwise: 3680 to 3920 mm Widthwise: 1740 to 1860 mm Heightwise: 1740
to 1860 mm.
2. Water Absorption Test : a. 24 hrs immersion cold water test: Brick specimens are weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The differences in weight indicate the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimens is taken. b. 5 hrs Boiling water test: Brick specimens are oven dried at 105°C- 115°C till it attain at constant mass. Cool the specimen at room temperature and record its weight. The specimen is immersed in boiling water for 5 hrs and water is allowed to cool at 27±2°c with brick immersed. The specimen are taken out and wiped with cloth. The weight of specimen is determined within three minutes. The difference in weight indicates the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. 3. Efflorescense Test: The presence of alkalis in brick is not desirable because they form patches of gray powder by absorbing moisture. Hence to determine the presence of alkalis this test is performed as explained below: Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well ventilated room. After all the water is absorbed or evaporated again add water for a depth of 25 mm. After second evaporation observe the bricks for white/grey patches. The observation is reported as ‗nil‘, ‗slight‘, ‗moderate‘, and ‗heavy‘ and serious. Results: (a) Nil: No patches
(b) Slight: 10% of area covered with deposits
(c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.
(d) Heavy: More than 50 per cent area covered with deposits but unaccompanied by flaking of the surface.
(e) Serious: Heavy deposits of salt accompanied by flaking of the surface.
Advantage of CEB Cost effective
Environmental friendly - conserves agricultural soil and non-renewable fuel
Provides better thermal insulation
Uses local resources
Appealing aesthetics - elegant profile and uniform size
Techno-economic characteristics/ Specifications Dimensional Variation +/-2 mm, Wet compressive strength 20-30 kg/cm2, Water absorption <15% by weight, Erosion <5% by weight, Expansion on Saturation-Expansion on Saturation, Surface characteristics-No pitting on the surface.
Sand Lime Bricks: Sand lime bricks are made by mixing sand, flyash and lime followed by a
chemical process during wet mixing. The mix is then molded under pressure forming the brick. These bricks can offer advantages over clay bricks such as: Their color appearance is grey instead of the regular reddish color.
Their shape is uniform and presents a smoother finish that doesn‘t require plastering.
These bricks offer excellent strength as a load-bearing member.
Refractory Brick: Refractory brick, also known as fire brick, is a type of specialized brick
which is designed for use in high heat environments such as kilns and furnaces. Numerous companies manufacture refractory brick in a range of shapes, sizes, and styles, and it can be ordered directly through manufacturers or through companies which supply materials to people who work with high heat processing of materials. High quality refractory brick has a number of traits which make it distinct from other types of brick. The primarily important property of refractory brick is that it can withstand very high temperatures without failing. It also tends to have low thermal conductivity, which is designed to make operating environments safer and more efficient. Refractory brick can withstand impact from objects inside a high heat environment , and it can contain minor explosions which may occur during the heating process. It may be dense or porous, depending on the design and the intended utility. This brick product is made with specialty clays which can be blended with materials such as magnesia, silicon carbide, alumina, silica, and chromium oxide. Using refractory brick which is not designed for the application can be dangerous, as the bricks may fail, cracking, exploding, or developing other problems during use which could pose a threat to safety in addition to fouling a project. Some places where refractory brick can appear include: fireplaces, wood stoves, cremation
furnaces, ceramic kilns, furnaces and some types of ovens.
TILES
A tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or even glass. Tiles are generally used for covering roofs, floors, walls, showers, or other objects such as tabletops. Alternatively, tile can sometimes refer to similar units made from lightweight materials such as wood, and mineral wool, typically used for wall and ceiling. Tiles are often used to form wall and floor coverings. Tiles are most often made from porcelain, fired clay or ceramic with a hard glaze, but other materials are also commonly used, such as glass, metal and stone. Tiling stone is typically marble, onyx, granite or slate. Thinner tiles can be used on walls than on floors, which require thicker, more durable surfaces. The following are the types of tiles: Tiles, being thinner than bricks, should be carefully handled to avoid any damage. Classification of tiles:
1. Common Tiles: These tiles are of different shapes and sizes and are used for flooring, roofing and
paving.
2. Encaustic Tiles: These tiles are used for decorative purposes in floors, walls, roofs and in ceiling. Based on the purpose of use of tiles: 1. Roofing Tiles 2. Flooring Tiles 3. Wall Tiles 4. Drain Tiles 5. Glazed Earthenware Tiles
Note: Refer Engineering Materials by R.K. Rajput for Complete Materials.
Terracotta: It is a type of earthenware, is a clay-based unglazed or glazed ceramic, where the
fired body is porous. Its uses include vessels (notably flower pots), water and waste water pipes,
bricks, and surface embellishment in building construction. The term is also used to refer to items
made out of this material and to its natural, brownish orange color, which varies considerably. In
archaeology and art history, "terracotta" is often used of objects not made on a potter's wheel,
such as figurines, where objects made on the wheel from the same material, possibly even by the
same person, are called pottery; the choice of term depending on the type of object rather than the
material.
Earthenware : Earthenware is a common ceramic material, which is used extensively for pottery
tableware and decorative objects. Although body formulations vary between countries and even
between individual makers, a generic composition is 25% ball clay, 28% kaolin, 32% quartz and
15% feldspar. Earthenware is one of the oldest materials used in pottery. After firing the body is
porous and opaque, and depending on the raw materials used will be colored from white to buff to
red. Earthenware is also less strong, less tough and more porous than stoneware, but is less
