L14. Glass, Ceramics & Textiles

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Learning Outcomes

By the end of this unit you should have developed a knowledge and understanding of:

what glass is and what it is used for
how glass has been replaced by plastics in products
how glass is made
a range of ceramics and products made from them
a range of natural and synthetic textiles
how textiles are used in products, fashion and interiors

None of these materials are explicitly mentioned in the AQA syllabus you are following but they are commonly used in product, fashion and interiors and you may need to make reference to them for comparison or contrast.

It is important that you are familiar with these three material categories but you should not expect to get questions in the exam that ask about these materials specifically.

They will be low on your list of priorities when revising but are nonetheless relevant and you may well make use of them in your NEA work.

Glass

Sand based materials

Glass

ceramic

Clay based

Pottery, earthenware,

textiles

Fibres

Cotton, silk,

polyester, nylon

Glass

There are a wide range of materials that can be classed as glass but for D&T, glass is essentially a material used for glazing windows, manufacturing bottles etc.

It is worth noting that glass is not currently listed in the materials section of the AQA course but in examination, and coursework, you may be asked to name a traditional material that has replaced glass or that is used as an alternative.

You should also understand what glass is made from and what properties it has which make it suitable for a variety of applications.

bottles

windows

drinking glass

Manufacturing with glass

Lime-Soda Glass is made from a mixture of sand, lime and sodium carbonate heated to 1500 degrees C in a furnace. The resulting molten material is tapped off to form a continuous flow that can then be ‘floated’ on a tank of molten tin to form glass plate.

During the process the glass sheet is annealed to reduce stresses that may have built up in the material. At the end of the process the material is cut to size using diamond wheel cutters. Glass made this way is a mixture of new and recycled materials (cullets). Up to 90% cullet can be included in the furnace.

Definition - Annealing: heat (metal or glass) and allow it to cool slowly, in order to remove internal stresses and toughen it.

Annealing

Glass like most materials contracts on cooling and when this happens internal stresses can develop between the surface and core of the material. To avoid this glass is cooled very slowly in an oven.

Glass blowing

Glass blowing is used to manufacture hollow objects such as bottles. Everyday projects made from glass use a ‘gob’ of glass that is formed by pressing and blowing into a mould

Mouth blowing is a traditional method restricted to more expensive pieces (see below 👇) of glassware

Slumping

Slumping is the process where glass is heated until it becomes soft at which point it can be moulded. Car windscreens are made this way.

Properties of glass

Glass is extremely brittle and will break if dropped or hit suddenly. It can also shatter if heated (or cooled) too quickly. Glass is much stronger in compression than tension and has excellent chemical resistance. It also has better optical properties than clear plastic which is why glass is till considered a premium material.

Toughened glass

Toughened glass is when glass is modified to make it harder to break. This involves reheating the glass then rapid air cooling which produces compressive forces on either side of the glass which make it much tougher. Because of this process, no further cutting or drilling can take place after it has been toughened.

Coloured glass

Coloured glass is simply glass that has had a colour introduced during

manufacture by the use of Copper, Iron or Nickel.

Lead crystal, Pyrex and laminated glass

‘cut

glass’

Adding lead oxide increases the way glass reflects light and is used in ‘cut glass’.

Pyrex

Pyrex is a brand name for heat resistant glass products made from

boro-silicate glass. These products can resist very high temperatures which

make them particularly suitable for cookware and lab equipment.

Laminated glass

is a very tough composite material made up of two thin sheets of plate glass which sandwich a tough polymer layer. If the glass is broken the polymer layer keeps the shards of glass together making it suitable for security applications.

Glass as a thermal insulator

Pilkingtons are possibly the largest UK manufacturer of glass and they developed a material that acts as an insulator to heat. This is known as K Glass and allows sunlight into a building while reducing the heat that escapes.

Self cleaning glass

Self cleaning glass is a relatively new development particularly useful for hard to clean windows such as those in very tall buildings. A special hydrophobic coating prevents droplets forming and interacts with UV light to break down organic dirt into compounds that can be washed away.

Similar hydrophobic and oleophobic coatings are used on modern day smartphone screens

Glass Vs Polymer

A common question in D&T exams asked why plastic has replaced glass in a variety of applications. You would need to know the properties of each in order to make such a comparison.

Here are a few advantages of each material:

Advantage of using polymers

they are lightweight (for transportation).

they have a lower melting point (for recycling).

they are impervious to gas (better for carbonated drinks).

they can be squashed without breaking (safer to use).

screw tops can be used.

Advantage of using glass

glass is more rigid and durable than thermosetting plastics.

glass is more scratch resistant.

glass has better optical properties; better transparency

glass is not deformed by heat like plastics are.

glass can be used where heat resistance is required

glass gives a sense of quality due to its weight and visual properties.

NOTE THAT: Due to its weight, glass is more expensive to transport, is less safe when damaged and (despite being very recyclable) requires a lot of energy to melt down.

Ceramics

Ceramics are often considered to be things like mugs and plates and decorative ornaments but there are a wide range of ceramic based products.

Most of the more common, everyday products are made from clay and at the top end of the market is fine bone china which actually uses finely ground animal bone to give it its translucent quality.

Engineering ceramics include things like house bricks and engineering bricks but also in electrical pylons and high temperature applications.

The list on the following page shows a range of metal oxide based ceramics and their applications.

Manufacturing ceramic products

The most traditional method of making objects in clay involves slip casting.

In this process liquid clay (slip) is poured into a mould. Before the clay completely sets it is removed from the mould so any finishing work can be done before the clay is glazed and painted (if necessary) before it is fired in a kiln. Once fired the clay becomes impervious to moisture and remains solid.

Textiles

A textile is a flexible material consisting of a network of natural or artificial fibers (yarn or thread).

Yarn

Yarn is produced by spinning raw fibres of Wool, Flax, Cotton, Hemp, or other materials to produce long strands.

textiles

Textiles are formed by weaving, knitting, crocheting, knotting, tatting, felting, or braiding.

Their sources can be natural (cotton, hemp, silk, wool etc.) which are derived from plants or other sources that can be grown

cotton

hemp

silk

wool

Alternatively, they can be synthetic (polyester, nylon etc.). These materials are made from polymers which are derived from fossil fuels such as oil.

Polyester

Synthetic fabric consisting of polymer. Can have hydrophobic and durable qualities.

nylon

Synthetic polymer based fabric. Strong, durable, water resistant.

Textiles can be categorised like this:

Plant

The oldest and most used textile. Derived from plant fibres Cotton, flax, jute, bamboo, hemp

Animal

Naturally produced from animals wool, silk

synthetic

Derived from polymers (oil) Nylon, polyester, acrylic

Natural textiles

Plants and animals are sources of natural fibres which can be made into yarn or threads to produce textiles.

Silk worms produce silk but this is often replaced by Nylon in cheaper products.

Wool comes from sheep while cotton and linen comes from plants.

Nylon - synthetic

Silk - silk worms

Cotton - plants

Wool - animals

Leather is not a textile (it is an animal hide/skin) but is often used in the production of furniture and interiors as well as products (iPad and iPhone cases)

Synthetic textiles

Several of the same polymers that are derived from oil can be spun into threads to make textiles.

Shirts, ties and jackets are often made from Polyester and stockings, which were once made from expensive Silk, are produced in mass using Nylon which has similar properties. Acrylic can be used as a fake fur materials and Elastane helps fabric like cotton to remain crease free. Kevlar is also a textile (see Modern materials).

Polyseter tie

Nylon stockings / tights

Acrylic "wool"

Elastane blended with cotton makes non-iron fabrics possible.

Summary

Glass is made primarily from sand and is a highly recyclable material with no shortage of source material.
Glass is still considered to be a premium material and used for higher quality laptop and phone screens as well as bottles for fizzy drinks, wines and beers.
Glass is also used for glazing purposes and is much more durable than polymers for this function.
Polymers such as PET have replaced glass in a variety of applications.
Ceramics are used for a wide variety of applications from plates and bowls to bricks and furnace linings.
Liquid clay is know as ‘slip’ hence the term ‘slip casting’.
A range of synthetic and natural textiles are commonly used in the fashion, furniture and automobile industries.
Fibres can be made from animals, plants or synthetic sources

Revision Notes

It is important that you are familiar with these three material categories but you should not expect to get questions in the exam that ask about these materials specifically.

They will be low on your list of priorities when revising but are nonetheless relevant and you may well make use of them in your coursework.

Prep 14

L14-Glass-ceramic-textile.ppsx

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