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LuxeSci Show Notes: S2E11 - Ceramics

Hello, welcome back to LuxeSci, a podcast to re-ignite your wonder by exploring the science of luxury items.  This week we’re moving away from paint as an art medium and into dirt.  Or more specifically, clay.  Clay is a humble material and yet it is turned into beautiful art by potters or ceramic artists.  Now i will admit to not knowing much about the world of ceramic art.  It’s not art that I usually gravitate to.  One technique that I really like is called Kintsugi, that’s where broken pottery is repaired with lacquer and gold and the seams are done in gold so you can see them.  It takes something that is broken and gives it a new life, all while acknowledging that it was broken.

Ceramics Background

  • The word ceramics comes from the Greek word Keramikos which means of or belonging to pottery.

  • There’s a neighborhood in Athens called Keramikos and that’s where all the pottery shops used to be

  • Ceramics - mixing substances, such as clay, with silica and heating them at high temperatures

  • Main difference between pottery and ceramics is that not all ceramics are made out of clay and are used in many forms.  Pottery is clay that has been made into a container of some kind.

  • Ceramics have been used for tens of thousands of years with the first earthenware figure dated to about 30,000 years ago and the first pottery vessel to around 18,000 years ago

  • The ancient Egyptians perfected glazing of pots around 7000 years ago and the Chinese improved the firing process to produce more highly decorated ceramics

  • Types of ceramics

  • Earthenware

  • Glazed or unglazed nonvitreous pottery

  • This means that it’s porous

  • Virtification - partial fusion of the clay as result of a firing process and is the full or partial transformation of a substance into glass (non-crystalline amorphous solid)

  • Heat the material until its liquid then cool rapidly.  We’ll cover this more when we do our episode on glass blowing

  • Normally fired below 1200C (2190F)

  • Otherwise known as terracotta

  • Absorbs liquid but can be glazed to stop that

  • Easier to shape with something like a potter’s wheel

  • Stoneware

  • Pottery fired at a relatively high temperature

  • Made from stoneware clay or non-refractory fire clay

  • Fired between 1100C (2010F) to 1300 C (2370F)

  • Developed after earthenware and before porcelain

  • Can sometimes be counted as porcelain

  • Vitreous or semi-vitreous

  • Porcelain

  • Vitreous pottery

  • Fired at between 200 and 1400 C (2200 and 2600F)

  • Greater strength and translucence than other types of pottery

  • Bone china

  • Composed of bone ash, feldspathic material and kaolin

  • Contains a minimum of 30% phosphate derived from animal bone

  • Strongest of the porcelains

  • Vitrified but translucent due to its mineral properties


  • This information comes from a great article from the Royal Society of Chemistry written by Stephen Breuer in 2012.

  • Basics

  • Ceramics are most commonly formed by clay. Feldspar minerals make up around 60% of the earth’s crust.  They are aluminum silicates that also contain alkali or alkaline earth metals. 

  • Feldspar minerals - aluminum tectosilicates that also contain sodium, calcium, potassium or barium

  • Silicon ions are linked by a shared oxygen ions to form a three-dimensional network - aluminum or silica ion surrounded by four oxygen ions and each oxygen ion is shared by a neighboring tetrahedron to form a 3-D network.

  • They crystallize from magma and are in metamorphic and sedimentary rocks

  • The clay is formed from the chemical weathering of these feldspar mineral rocks.  

  • Low concentrations of carbonic acid (from rainwater or plant roots) breaks the bonds between the aluminum and the oxygen and releases other metal ions and silica

  • Clay formed depends on the composition of the source rock and the climate

  • Kaolinite - one important mineral which contains 1:1 silicon to aluminum oxides.  Arranged in plate-like particles and stacked in layers linked by hydrogen bonds

  • How do you make a ceramic pot, for example.  First, you take some clay, add a bit of water and shape the pot

  • This is the result of the clay layers being separated by a thin layer of water molecules that are linked to neighboring layers via hydrogen bonds

  • This is what is called a weak force - the bonds can flex when force is applied to shape the clay but strong enough to stand on their own when force is removed.

  • As the clay dries the water molecules escape from in between the clay sheets and the clay shrinks a bit.  The components of the clay become bonded to each other, instead of the water and form a stronger structure

  • However, that pot will dissolve in water again until it is heated

  • Interestingly, after the temperature reaches 500C, the changes to the pot become irreversible.

  • The clay is fragile and crumbly but can’t be reconstituted to the original workable state

  • Chemically what is happening is that more of chemically bound water is being removed and the weak hydrogen bonds are replaced by stronger and shorter oxygen bridges

  • The regular sheet-like crystal structure of the kaolinite is being lost and a more amorphous metakaolinite is being formed

  • Heat the pot to 1000C to produce biscuit ware, which is strong but porous

  • If you’d like a stoneware or porcelain pot, you can increase the temperature so that the virtification process starts, melting some of the components of the clay to act as glue to hold provide additional strength

  • Metakaolinite transforms into mullite that forms needle-like crystals and the feldspar melts into glass

  • At these temperatures all the water in the clay is gone.  You can visualize that easily be taking an earthenware cup and a stoneware cup and microwaving water in them.  The handle of the earthenware cup will be hot as well as the water, but the handle of the stoneware cup will not.  That’s because there is still some water in the handle of the earthenware cup and since microwaves heat water by causing water molecules to move faster, the handle will be hot too.

  • You could stop there, or you can glaze your pot.  Glazing makes earthenware ceramics non-absorbent and also adds a bit of decoration

  • Glazing - covering a work in a thin coating of glass

  • Glazes usually have 3 components

  • Silicon dioxide 

  • Aluminum oxide to enhance viscosity - crosslinks the silica networks

  • Fluxes (earth metal oxides) to lower the melting point of the mixture to the temperature of the firing

  • Transition metals provide the color of the glaze - copper, manganese, chromium, cobalt

  • Most common are iron, copper and cobalt

  • Iron is most versatile. It can give red, yellow, brown, blue and green colors depending on the firing conditions and the mixture of the glaze

  • Phew!  Who knew that there were so many components, chemical bonds, chemical processes

  • Fun side note - there is currently research going on to create virtual reality pottery experiences.  


Engineering Uses for Ceramics:

In Electric Vehicles

One major goal in the creation of electric vehicles and hybrid vehicles is the electronics package that enables the operation of an electric motor. A lot of power is needed to flow into the motor but the only way to do it is with electronic semiconductors that can handle a bit of heat. Ceramic electronic packages are part of the way this is done.

Alumina and aluminum nitride ceramic plates can be plated with copper and then patterned to create channels for current to flow to semiconductor devices that can be soldered to the surface of the metals. Additionally ultra-high temperature electronics can use a secondary ceramic composed of sintered nano-silver particles instead of metal to create a conductive base for the semiconductor chips. The result is a tightly packed electrical power converter that takes up a very small space for electric vehicles. 

Porcelain: (Encyclopedia Britannica)

porcelain, vitrified pottery with a white, fine-grained body that is usually translucent, not to be confused from earthenware, which is porous, opaque, and coarser.

In China, porcelain is defined as pottery that is resonant when struck. In the West, it is a material that is translucent when held to the light. 

The word porcelain is derived from porcellana, used by Marco Polo to describe the pottery he saw in China.

The three main types of porcelain are true, or hard-paste, porcelain; artificial, or soft-paste, porcelain; and bone china. Porcelain was first made in China—in a primitive form during the Tang dynasty (618–907) and in the form best known in the West during the Yuan dynasty (1279–1368). This true, or hard-paste, porcelain was made from petuntse, or china stone (a feldspar type rock). The rocks are ground into powder and mixed with kaolin (white china clay). During the firing, at a temperature of about 1,450 °C (2,650 °F), the petuntse vitrified, while the kaolin ensured that the object retained its shape.

What is vitrification: This is the full melting of a substance into glass (a non-crystalline amorphous solid). The result being a water-tight barrier to eliminate the potential to hold on to bacteria.

 Attempts by medieval European potters to imitate this translucent Chinese porcelain led to the eventual discovery of artificial, or soft-paste porcelain, a mixture of clay and ground glass requiring a “softer” firing (about 1,200 °C, or 2,200 °F) . Although there is a superficial resemblance, artificial porcelain can generally be distinguished from true porcelain by its lower density and hardness. It can be cut with a file, for example, whereas true porcelain cannot, and dirt accumulated on an unglazed base of soft porcelain is hard to remove but easily removed from true porcelain.

The first European soft-paste porcelain was made in Florence about 1575 at workshops under the patronage of Francesco I de’ Medici, but it was not until the late 17th and 18th centuries that it was produced in quantity. The secret of true porcelain, similar to the porcelain of China, was discovered about 1707 at the Meissen factory in Saxony by Johann Friedrich Böttger and Ehrenfried Walter von Tschirnhaus. The standard English bone china body was produced around 1800, when Josiah Spode the Second added calcined bones to the hard-paste porcelain formula. Although hard-paste porcelain is strong, its vitreous nature causes it to chip fairly easily, whereas bone china does not. Hard-paste porcelain is preferred on the European continent, whereas bone china is preferred in Britain and the United States.


  • Vitrification - turning into glass

  • Glazing - covering ceramics with a thin coating of glass

  • Chemical weathering - corrosion or degradation caused by chemical reactions

Cocktail party facts

  • What is clay made of - feldspar minerals

  • Why do the handles of certain mugs get hot in the microwave

  • What happens to the clay during the firing process

Thank you for listening to this episode of LuxeSci.  Please tell at least two people about this podcast.  This is the best way to help us get noticed and find new listeners.  A special thanks as always to my audio engineer Dimos.  Our theme music is Harlequin Mood by Burdy



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