Properties of Clay Plasticity – The physical property that allows clay to keep any new form it is given. Clay and soil have essentially the same chemical makeup or formula. The reason clay is plastic is due to the physical difference, not the chemical.
Stages clay goes through as it dries: Slip – a mixture of clay and water used in joining clay and decoration
Plastic Clay – clay that is workable and can retain its form given
Leather-hard Clay – clay that has dried past plastic, but before bone dry, clay in this stage can still be joined and carved
Bone Dry Clay – Clay in which most of the water has evaporated out
Forces That Work On Clay
The Artist: The artist forms the clay.
Evaporation: Clay dries when exposed to the air. Humidity (moisture in the air) controls the drying rate.
Absorption: Water in the clay is absorbed by the hands and surfaces upon which the clay is worked.
Shrinkage: As the clay dries, it gets smaller. As the clay is fired its shrinks at a specific shrinkage rate as determined by the type of clay.
Gravity: Wet clay is weaker than dry clay and can “Slump” due to gravity. When designing pottery, keep this force in mind because it can affect the feasibility and difficulty of construction.
Basic Pottery Terms Ceramics – the art of making and firing items using clay Pottery – items made out of clay, usually includes vessels and functional items
Vessel – a container usually associated with holding liquids
Greenware – any unfired clay, note unfired clay can be recycled, however once it has been fired it cannot be recycled
Bisqueware – ware that has gone through the first firing, low temperature and still remains porous
Grog – crushed ceramics or organic material that makes clay more porous
Functional – refers to pottery that has a use (example: cup, bowl, or plate)
Non-Functional – refer to pottery with no specific use can be sculptural in nature.
Types of Clay Clay Body – this is a mixture of clay, minerals, and a variety of other ingredients that make up a type of clay
Earthenware – low fire clay that remains porous after firing.
Stoneware – mid to high fire clay that is dense, non-porous, and hard after firing.
Porcelain – high fire clay that is pure clay and is usually translucent.
Kaolin – or pure clay, typically used in white clay bodies like porcelain
Construction Methods and Processes The Slip and Score Method of Joining Clay 1. Make sure both piece contain about the same amount of water (Moisture Content).
2. Score both surfaces to be joined
3. Add slip to one surface
4. Join with force
5. Smooth across the seam
Wedging Clay – Eliminates air bubbles and makes the clay more consistent. Types of wedging are Kneading, Wedging, Spiral Wedging and Ram’s Head Wedging
Pinch Method – Refers to the method of squeezing clay between your thumb and fingers. One basic form would be a pinch pot which is usually formed using one piece of clay.
Coil Method – This method of forming clay requires you to roll out long coils that are added to a base. This method allows you to use smaller pieces to construct a larger from allowing you also to control the moisture content more easily.
Slab Method – This method uses slabs of rolled out clay to join to together to make vessel. This method also allows you to make larger pieces however additionally this process can be used to make larger surface areas and more geometric forms that would not be as possible using the other methods.
Wheel Throwing – This method uses a potter’s wheel to shape the clay, also known as throwing. The wheel creates centrifugal force that allows the artist to create forms quickly.
Kilns and Firings Kiln – is an enclosed structure used to fire clay up to high temperatures. Kilns can be fueled using different materials – electricity, natural gas, wood, coal, propane or oil
Firing – heating clay to high temperatures in order to make it durable and strong
Pyrometric Cones – (Cones) are small cone like shapes that are comprised of ceramic materials designed to bend when a certain temperature is reached
Low fire – refers to clays and glazes fired to cone 015- cone 02
Low-mid fire – refers to clays fired to cone 01 – cone 3
Mid fire – refers to clays and glazes fired to cone 4 – cone 7
High fire – refers to clays and glazes fired to cone 8 – cone 12
Vitrification – clay becomes hard, dense and non-porous and glasslike in nature, this typically occurs during the glaze firing
Stages of Firing’s Bisque Fire – Unglazed pottery is fired to a temperature that will make the clay strong but porous (Having Minute passageways). Porosity is necessary for the clay to accept the glaze. During this firing the clay will shrink in size, the percentage that the clay shrinks is called the shrinkage rate.
Glaze Fire – Glazed pots are fired to a temperature that will cause the clay to become vitreous (hard, dense and non-porous) and the glaze will mature and form a glass-like substance.
Types of Kilns Updraft Kiln – is a kiln that draws heat and flames up through the top of kiln
Downdraft Kiln – a kiln that draws the heat and flames down through opening located at the base of the kiln
Parts of a kiln Chamber – the area inside the kiln where pottery is placed to be fired
Firebox – the section of the kiln where the fuel is added
Flue – an opening in the kiln that allows gases to escape as pottery is fired
Muffle – the area of the kiln that protects the pottery from the direct flame, not found in all kiln setups
Peephole – a hole in the kiln that allows the operator to view the firing as it progresses Atmospheres in Kilns Oxidation Atmosphere – an environment created during firing in which oxygen is introduce into the kiln
Reduction Atmosphere – an environment created during firing in which oxygen is restricted into the kiln
Basic Parts of Pottery Vessels Foot – the base of the vessel upon which it stands
Body – the main part of a vessel, usually the largest Shoulder – the part of the vessel that curves typically inward as it approaches the neck
Neck – the narrower part of the vessel between the shoulder and lip
Mouth – the opening of the vessel
Lip – the rim at the top of the vessel
Advanced Hand Building Techniques Molds – a form used to shape clay Press Mold (also known as a Sprig Mold) – open form one piece molds into which the clay is poured or pressed Hump Mold (also known as a Drape Mold) – a convex support mold that holds clay in a certain shape until it hardens Slump Molds – a concave support mold that holds clay in a certain shape until it hardens Maquette – a small, quickly made preliminary version of another larger piece to be created similar to a sketch used in drawing Relief – Sculptural techniques that uses raised surfaces that project from the background
Low Relief – (also known as bas-relief sculpture) – this type of relief uses forms that project only slightly from the background and has a shallow depth
High Relief – In this type of sculpture, the forms project further out from the background, has a greater depth and makes use of larger undercuts that show more form
Pulling – stretching or stroking plastic clay to elongate the clay typically used in creating handles
Extruding – shaping clay by forcing clay through a die to give it a variety of shapes
Wheel Throwing Techniques Wheel Throwing – This method uses a potter’s wheel to shape the clay, also known as throwing. The wheel creates centrifugal force that allows the artist to create forms quickly.
Centering – the process of aligning the clay on the wheel head to correctly position the clay and make it even Opening – the process of making an hole in a centered piece of clay, this process allows the clay to be shaped into its basic form
Trimming – the process of removing clay when the piece has reached the leather hard stage. This process can be used to create a foot on a wheel thrown vessel or trim the vessel to its intended form Potter’s Wheel – A device used to throw clay forms or vessels. They can either be manual or human powered (Kick Wheels) or electric.
Wheel-head – the flat plate that rotates on the potter’s wheel and is the surface on which clay is thrown.
Bat – can be used as a base for working with clay these can typically be made out of plastic, plaster, wood
Chuck – a clay form that can be used to trim leather-hard pieces of clay
Calipers – a tool that has a hinge used in measuring diameters of clay work
Decorating Techniques Burnishing – uses a smooth object to polish the surface of a leather hard piece that produces a shine when firing at low temperatures
Incise – the process of removing by carving
Inlay – Filling in impressed or incised areas in your clay with colored clay
Mishima – Filling in impressed or incised areas in your clay with a colored slip
Paddling – hitting the clay with a flat piece of wood to create strong joints, alter the shape and add texture to clay Piercing – uses a variety of tools to cut holes in clay as decoration
Sgraffito – a process in which colored slip is added to the piece and scratched through to reveal the clay body beneath
Slip Trailing – a process that uses lines or shapes of slip as a decoration
Sprig – a relief decoration that is attached to a piece with slip
Glaze Information and Techniques Glaze – a glasslike substance comprised of three basic ingredients: silica, flux, and alumina
Three Basic Ingredients in Glazes Silica – referred to as the glass former. This is most commonly found in sand
Flux – reduces the temperature at which silica melts
Alumina – stabilizes the glaze to keep the glaze from running off the piece
Glaze Related Terms Underglaze – oxides or commercial colorants, applied before glaze application
Overglaze – a glaze designed to go over another glaze after the piece has been fired once
Stains-pigments used for coloring clay bodies and glazes.
Engobe – slip that contains colorants
Luster – a decoration that creates a metallic sheen to a glazed surface
Oxide – a compound used coloring clay bodies and glazes it is comprised of oxygen and other elements
Carbonates – a compound used coloring clay bodies and glazes it is comprised of carbon and other elements
Colorant – a compound or element that can be added to create color in clay, slip, and glaze
Opacifier – an element that can be added to glaze to make a glaze opaque
Translucency – glaze that allow light to pass through
Matt – dull surface in glaze
Glossy – shiny surface in glaze
GLAZE APPLICATION Spraying – a method of applying glaze with a spray gun
Dipping – a method of applying glaze to a piece by immersing it in a container of glaze
Pouring – a method of applying glaze to by pouring glaze into or on the piece
Brushing – a method of applying glaze using even brush strokes can be used to avoid thick deposits of glaze where strokes overlap, also may require several coats depending on the glaze
Dry Footing – removing glaze from the bottom rim of a piece so that it can be fired standing on a kiln shelf, without stilts
Wax Resist – the application of melted wax to the foot or body of a clay object to resist the glaze
DEFECTS IN GLAZES Blistering – this is cause by gases escaping when a glaze is firing too fast or the coat of glaze is too thick
Crawling – a glaze defect in which the glaze rolls away from areas of the piece it is on leaving bare parts
Crazing – a glaze defect resulting from lack of fit between a glaze and the body it is on so that fine cracks appear on the glaze
Running – this defect occurs when a glaze has too much flux this cause the glaze to run down the pot onto the kiln shelf, it may need to be broken away from the kiln shelf to remove
Pinholes – a glaze defect caused by rapid firing, rapid cooling, or by tiny air holes in the clay