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Metals, Ceramics and Glass: Properties and Processing

Metals bend before they break and can be shaped hot or cold. Ceramics are hard, heat-proof but brittle. Glass is clear and brittle when cold, and soft and shapeable when hot. Each is made into things by a different process.

🎬 Step-by-step story

  1. Three inorganic families: metal, ceramic and glass. They come from rocks and sand, not from living things. This is a steel bar on a test bench.
  2. Put a load on cold metal. It bends. Take a big load away and the bar stays a little bent. Metal gives a warning before it fails.
  3. Now heat the metal red-hot. A small load bends it a lot. This is why smiths heat metal to forge it into shape.
  4. Try a ceramic tile. It does not bend at all. At one load it snaps. Ceramic is hard and heat-proof but brittle.
  5. Cold glass is brittle too. A small load and it snaps. But glass is clear and does not rust.
  6. Heat glass until it glows. Now it is soft and sags. This is how glass is bent and blown. Use the sliders and test all three.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

🤔 Common doubts, cleared

Why does metal stay bent but a plastic ruler springs back?

Past its yield point, metal bends for good. Many other materials spring back until a larger load.

Why do smiths heat metal first?

Hot metal is soft, so a small hammer blow shapes it. You can see the bar bend easily in the 3D.

If ceramic is so hard, why does it break?

Hard means it resists scratches. Brittle means it cannot bend. Ceramic is hard and brittle.

Why does glass break so easily?

Its jumbled atoms cannot slide, so small cracks spread fast and it snaps.

How can glass be bent into bottles?

Heat makes it soft like thick honey. Then it can be blown or pressed.

Metallic materials

Metals are shiny, heavy and carry heat and electricity well. They are ductile: they can be stretched into wire. They are malleable: they can be hammered flat. A metal bends before it breaks, so it gives a warning.

Iron and steel are strong and cheap. Steel is iron with a little carbon. Aluminium is light and does not rust. Copper carries electricity. An alloy is a mix of metals that is better than one metal alone, like brass (copper and zinc).

How metal is processed

Casting: pour melted metal into a mould. Forging: heat metal and hammer it. Rolling: press it into sheets. Machining: cut, drill and turn it. Welding: join pieces with heat. A surface coat, such as paint or zinc, stops rust.

Ceramic materials

Ceramics are made from clay and other minerals. Clay is shaped while wet, dried, then fired in a kiln at high heat. Firing makes it hard and stone-like.

Ceramics are hard, do not rust, and keep their strength in very high heat. That is why bricks, tiles, cups, toilets and furnace linings are ceramic. Their weakness is brittleness: they do not bend, they crack. A glaze (a thin glassy coat) makes a ceramic smooth and waterproof.

Modern fine ceramics are used in spark plugs, knives and computer parts.

Glass

Glass is made by melting sand (silica) with soda ash and limestone. The melt is cooled fast, so the atoms freeze in a jumbled way. That is why glass is clear.

Cold glass is hard, clear and does not rust, but it is brittle. When hot it is soft, so it can be blown, pressed or drawn. Sheet glass is floated on melted tin to make it flat. Toughened glass is heated and cooled quickly, so it is stronger and breaks into small blunt pieces.

Try it: the bend-or-snap test

Try it in 3D: pick a material, slide the load up, then take it away. Does it bend, stay bent or snap? Now slide the heat up and try again. At home: bend a paper clip (metal) and see it stay bent. Never try to bend glass or ceramic.

Key formulas and definitions

Worked examples

1. Why is a steel bridge safer than a glass bridge if it is overloaded?

Steel is ductile, so it bends first and gives a warning. Glass is brittle and snaps without warning.

2. Why is a furnace lined with ceramic bricks, not metal?

Ceramics keep their strength at very high heat. Many metals soften or melt at that heat.

3. A blacksmith makes a horseshoe. Which steps does the metal need?

Heat the iron red-hot (it turns soft), hammer it into a curve (forging), then cool it. Hot metal bends with a small load.

Common mistakes

Practice quiz

1. Which material bends before it breaks?
2. Firing in a kiln is used to make:
3. Glass is mainly made from:
4. Casting means:
5. Toughened glass is made by:

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

What is the difference between ductile and brittle?

A ductile material, like copper, stretches or bends before it fails. A brittle material, like glass or ceramic, cracks with almost no bending.

Why is glass transparent?

Light passes straight through it because it has no tiny crystal edges to scatter the light. Its atoms are jumbled but evenly spread.

Are ceramics and glass the same?

No. Both are inorganic and brittle, but ceramics are made from clay and fired, usually opaque. Glass is made from melted sand and is usually clear.

Where this is taught

Japan高校（専門学科）1〜3年Design Materials

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