Clay (L16) Flashcards
What are the 3 ways clay can be referred to?
- a type of mineral
- sediment grain size
- a mass of minerals that behave plastically when wet
What is a ceramic?
a hard, brittle, nonmetallic material made from clay and other Earth materials and hardened by firing at high temperature
what kind of structure does a ceramic have?
a crystalline structure
what are the basic building blocks of clay?
- sheets of linked silica tetrahedra
- sheets of linked alumina octohedra
3.assorted positively charged ions that bond these sheets together
2 common clay minerals?
kaolinite and llite
what is the main property that makes clay an amazing medium in art applications?
the shape of its crystals
Clay mineral crystals have a ____ cleavage in ____ direction
perfect, one
what does it mean for clay mineral grains to be wide and flat?
means that under weak stress, when it is being deformed, the plates can slide past one another, allowing the mass of clay to deform very easily
what makes clay so cohesive?
the high surface area of the mineral grains
clay minerals can be produced from the weathering of which mineral?
fledspar minerals
the 2 ways we loosely categorize clay into?
primary clays - found in original site of formation (contain kalolinite)
secondary clays - transported form original site of formation (contain kaolinite but as well as other minerals)
what is the body of blended clay called?
clay body
what are the 3 ways clay bodies can be categorized into?
Earthenware, stoneware, and porcelain
what is grog and what does it do?
a low-porosity material that are added to some claybodies which retains heat and adds a rustic appearance, adds strength to clay, and reduces the overall shrinkage rate
What is earthenware?
composed largley of secondary clays
cheapest type of clay body (creates mugs, plates, flowerpots)
what is an advantage of using earthenware for flowerpots?
earthenware is porous and permeable so can allow air and water to move through the walls of the pot
what is stoneware?
made mostly from primary clays and used to make items that are harder and stronger than earthenware
impermeabel to water so used to make floor tiles and drainage pipes
What is porcelain?
“upper-class” category of ceramic made from primary clays
finest texture of all of the ceramics, great strength (used for thin objects, such as fine dinnerware) and transluscent
how can porcelain have such smooth surfaces?
doesnt use grog
what are the 3 main methods of producing a ceramic piece?
Handbuilding
Throwing
Slip-casting
What is handbuilding?
forming an item in a freeform manner without a potter’s wheel
What is Throwing?
clay that is shaped on a spinning potters wheel
What is slipcasting?
clay that is made by producing a cast inside a mould
What is the process of creating a ceramic?
- Shaping
- Air-drying
- Firing: Kiln Drying
- Glazing
What must be done during the Air-drying process?
a ceramic piece must be air-dried to a “greenware” state before it is fired
What happens during Kiln Drying
complete drying happens here and elimination of all of the free water only happens when the boiling point of water has been reached
What happens during the major transformations of the clay?
the clay loses its hydrogen and oxygen as water and the remaining material produces mullite and quartz
what is mullite?
an aluminim silicate mineral that laces the structure together, giving it cohesion and strength
what happens when the ceramic is finally cooled?
the mullite crystals interlock and become glass to bind the whole structure together
At what point in temperature does Primary clay and Secondary clay vitrifiy in?
primary clays - high temp
secondary clays - lower temps
what do you call a ceramic that has been fired in a kiln but has not yet been glazed?
“bisqueware”
What is glaze?
a form of glass consisting of glass-forming minerals, and gives the ceramic its beauty in color and finish and waterproof
what are 2 common additives used to increase the opacity of glazes?
titanium oxide and tin oxide
