How to Make Coloured Pottery

The Appeal of Colour

Copper Ruby glaze

The addition of colour to pottery adds so much to its appeal. Whilst white pottery can emphasise the distinctive form of a piece it is often colour which catches the eye! Colour is often associated with a mood or feeling and this varies between cultures and countries. For example red is a very emotive colour and can mean anything from love and romance to danger and fire! Choosing the right colour to make or decorate your pottery however is a matter of personal choice and allows for much creativity and freedom of expression.

Colour can be added to pottery in many ways including body colour, underglaze, inglaze, onglaze and also as a component of the glaze itself.

In this article I will try to review the two main types of ceramic pigment ( raw oxide and ceramic stains) available and how they can be used to produce highly decorative pottery.

In the second of my series on glaze I described how to make a white textured stoneware glaze. 
Simply adding inorganic colouring oxides such as Iron Oxide to such a glaze produces colour but not always the desired colour!  Carry on reading to find out why!

Raw Oxides in Coloured Glaze

Top = Oxides in transparent glaze
Bottom = Oxides in opaque glaze

Copper oxide crackle glaze

It is common for raw oxide pigments to be used used in pottery making. Many studio and craft potters prefer to use cobalt oxide, chrome oxide, Iron oxide and copper oxide as colouring pigments.These oxides give blue, green, yellow-brown, and green-blue respectively on firing in or under the glaze. Often the fired colour of the starting oxide is not the same as the original oxide colour e.g. cobalt oxide changes from black to blue on firing in a glaze. However mixing of these oxides in a glaze, gives variable but often aesthetically pleasing artistic effects on firing. It is for this reason, and the lower cost involved that many studio potters often use these materials.

Iron Oxide and cobalt oxide in glazes

In using oxides as pigments It is important to match the pigment type and content to the glaze to achieve the most consistent results. In the example above iron oxide gives a yellow colour when added to a glaze in small percentage (eg 1%) compared to a brown colour in high percentage (eg 15%). In combination iron oxide and cobalt oxide often give grey or a black glaze colour (see example right). The difference in the colour between an opaque and transparent glaze containing the same pigment content is also marked. In the example above the same pigment content is compared in a transparent glaze (top) and an opaque glaze (bottom). A stoneware textured glaze will produce colour tones similar to those of an opaque glaze.


Organic pigments such as those used in paper printing are clearly not suitable and will simply burn away during firing

Ceramic Stains in Coloured Glazes

Top = Ceramic stains in transparent glaze
Bottom = Ceramic stains in opaque glaze

In contrast to raw oxide pigments, ceramic stains have been specially formulated to create a wide range of colour tones in glaze. In their manufacture they have undergone a heat process and a fine grinding process so that they are highly temperature stable and capable of being mixed together to generate intermediate colour tones. This property is highly valued by large scale manufacturers who need consistency of colour tones. However this all comes at a cost compared to raw oxides.

Onglaze and Inglaze Decoration

Pantone Mugs showing onglaze colours

It is common for high quality whitewares such as bone china and porcelain to be decorated with special colours called onglaze (low temperature) or inglaze (high temperature). These colours use a mix of special fluxes and the ceramic stains identified above to create a wide range of intense, durable colours and bond them to the already fired glaze surface.. Whilst a few studio potters try to make their own, they are best supplied by specialist manufacturers to ensure they meet current legislation and perform satisfactorily in use. These colours are often supplied as powders or pre-dispersed in a liquid allowing them to be applied by hand painting or screen printing. This type of colour is very versatile and is often used to make precision decorative decals for water slide application onto pre-glazed pottery. A new development called Digital printing now allows these decals to be personalised and produced in small quantities making it a cost effective method of decoration for craft and hobby use.

Summary

Clearly there is more to making coloured pottery than is immediately obvious. For those who want consistent colour that can be mixed to give intermediate shades then use ceramic stains either as a glaze component or in decoration products such as inglaze or onglaze colours. For those who want unpredictable but aesthetically pleasing results use oxides as a glaze component or under the glaze. Whichever option you choose using colour creatively will only add to the appeal of your pottery.

Happy Potting
The Potters Friend

More information and other technical articles on pottery and ceramics can be found at my website The Potters Friend.

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Top 10 Pottery Making Tips for the more experienced Potter

Pottery making is a fun but sometimes frustrating hobby. You never know exactly what your results will be when you open that kiln door! Here are my tips to make pottery making that little bit more rewarding......

1. Keep records of everything you do-that way you learn quickly and can repeat your successes and avoid your failures.

2. Label your buckets not your lids- don't learn the hard way that you have just glazed your speciality piece in the wrong glaze!

3. Buy a kiln with a modern controller. Modern controllers are now relatively inexpensive and give you such freedom to control the firing in a way that best suits your product.

4. Keep drying of your product consistent. Drying too quickly is one the most common causes of glaze or clay faults.

5. Learn something about the materials you use. Armed with a little knowledge you can save so much time.e.g. Does glaze go off? What happens to my clay if it freezes?

6. Keep your clay in good condition by covering it with plastic when not in use. That way it retains its plastic condition.

7. Plaster moulds need to be replaced after 40-50 casts. It is false economy in slip casting to continue to use old moulds. These may give inconsistent thickness, pinholed ware and much more besides!

8. Use Orton cones or Bullers rings in your kiln. That way you know your kiln is performing OK and you can spot potential problems such as element failure before they become disastrous.

9. Give some pieces to your loved ones or to charity. The feel good factor will keep you motivated.

10. Continue to share your passion with others. Go to pottery classes and learn something new or join an online pottery group.



Alternatively why not test your pottery knowledge with my quick pottery quiz

More information and other technical articles on pottery and ceramics can be found at my website www.pottersfriend.co.uk

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What is a glaze?

A mature pottery student recently asked me the question 'What is a ceramic glaze?' I hesitated whilst contemplating how to answer what initially seemed a very simple question. In the end I gave him 2 answers , a non technical one and a technical one. The precise amount of information he required depended much on how he wanted to use the information.

Sometimes too much information only leads to confusion!

For example an evening class student wanting only to paint pottery and later have it glazed and fired by an established potter needs only basic information.

In contrast a student studying pottery making and ultimately wishing to make and fire his own glazes needs a much more detailed chemical approach.

The Answers

These are the answers I gave him:-

1) A pottery glaze is a glassy coating applied to the surface of a ceramic to create a smooth, impervious, and decorative finish.

2) A pottery glaze is a mixture of ceramic materials which may often include minerals such as felspar and silica, a glass like component such as frit, clay as a suspending agent, and pigment as colouration. Many other minerals or oxides may also be used. These materials are finely ground in water to produce a glaze slip. Other organic and inorganic additives may at this stage be added to aid application. The slip is then applied to the ceramic body and fired to a sufficiently high temperature for the components to physically and chemically react to form a smooth glassy coating that bonds strongly to the body. Normally a temperature in excess of 1000C is required.

Do you have any simple questions you want answering? Please let me know.

More information on pottery making can be found at my website The PottersFriend