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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Digital printing of ceramics

Digital printing of ceramics and decals

Digital printing of decals and ceramic tiles is already well established. Computer generated images can be printed directly onto ceramic tiles via special inkjet systems. Alternatively a photocopier type system can be used to print onto decal paper. Of course both these systems require special machines and ceramic inks or toners to produce optimum results. Nevertheless these systems are causing a revolution in the ceramic tile industry.

The detail of decal printing

Ricoh desktop ceramic printer

In the case of digital decal, you can either create a drawing or photograph and then convert it to a digital image suitable for printing on to decal paper. The image is produced as a decal by a photocopier type machine. After printing the image is sealed to the paper with a covercoat and allowed to dry. The decal can then be applied in the same way as conventional decals by a water slide method. Decorators have the choice of either outsourcing decals (small quantities) or for large quantities buying a machine and toners and printing themselves..

The detail of ink jet printing of tiles

Pigment	System	Temperature	Colour
Yellow	Zr-Si- Pr	1250 °C
Red Magenta	Zr-Cd-Si-Se	1250 °C
Cyan	Zr-V-Si	1250 °C
Black	Fe-Cr-Co-Ni	1250 °C
Primary 4 colours used in ink jet printing

In the case of ink jet printing, the digital image is converted to a ceramic image using a specially adapted ink jet printer and special inks. The ceramic tile passes beneath the printer head and the ink jet colour nozzles deposit the image on the tile.

Gamma Ink Jet Tile Printer

Typically up to 10 ceramic colours are used to produce high quality digital images, 4 similar to the primary colours shown above plus additional spot colours. Browns, coral reds and white are commonly used to fill gaps in the colour space. Special printer heads are used to cope with the highly abrasive ceramic inks. For maximum definition and colour intensity special glazes are sometimes used as the base for printing the coloured image. The printed item can be fired almost immediately after drying.

3d Printing of Ceramics

I am constantly amazed at the ceramic challenges I see each year. Whilst making pottery and ceramics is an ancient tradition, new industrial processes and products (or the re-introduction of many older techniques) continue to stretch the imagination.

3d printed sugar bowl

Both in the UK and USA, 3 dimensional digital printing is one such technique. Developed initially for rapid prototyping of plastic objects it is now being used for small special ceramic parts. The potential to build up a ceramic mug  layer by layer  from a computer image is certainly feasible.
 I have seen the initial prototypes which have been glazed and fired. Many technical challenges remain for this process to be viable commercially but I have no doubt that in the long term this will happen.
For more information about this technique see the link project below:-
 University of Bristol project

3d printing using liquid clay syringe

3d extruder printing

This type of printing is also in the early stages of development for ceramics. Many questions remain particularly control of rheology and removing air pockets and machine development.. However the picture on the right shows how the process works. An air powered syringe forces liquid clay out of the nozzle to build up the object in layers. The head could be computer controlled to map out a digital design.
Potentially the ceramic designer can be creative in designing complex forms as well as simple shapes.
Picture and link to more information kindly provided by Ceramic 3D Extruder (FabLabZuidLimburg) / CC BY-NC 3.0

So what does this mean to the hobby or studio potter?

The opportunity to make low cost efficient designs which can be personalised to meet your customer needs. Digital ceramic decals are already established and widely available. But keep following the progress of 3d printing as the potential is endless. Perhaps now is the time to look at ways these techniques can expand your opportunities?

More information and other technical articles on pottery and ceramics can be found at my website The Potters Friend. Go now to sign up for my free newsletter.