This project is the first in a series on adding colour to clay for different effects. You will learn how to colour your clay, then use it in combination with other colours to make exciting and unique forms in an array of patterns.
We begin at a very basic level because this is a vast and often technical subject that can’t be fully covered in one go, but we will introduce more complicated techniques
You will need:
Porcelain or other white-firing clay– a white-firing clay is best for colour take-up
A selection of body stains and/or oxides
Scales; one for clay and one capable of measuring in one-gram increments, for the colourants. One set might do both, or you may need two sets
Water and small vessels for mixing the colours in
Health and safety:
Stains and oxides are toxic if inhaled or ingested – WEAR A DUST MASK when mixing, and rubber or latex gloves to protect your skin.
Before you begin: Some general information
Tips to get started
There are two methods for mixing colour into clay – wet and dry. The wet method involves less work and isn’t complicated, but it is messy! This is the method you will learn in this issue.
It should be said that makers working professionally with coloured clays have their preferred method for mixing – some like to mix into dry clay, others into wet, some like a delicate palette of shades, others, more vibrant colours, therefore ultimately, they devise a way of working to suit their own vision. To arrive at a colour palette you really like, you will have to do as professionals do – many tests!!
Stains and oxides
The general guideline for quantities of colour is anything from 0.5% – 20% depending on the firing temperature of the clay. Most stains will provide vibrant colour at or above cone 5/6 (1180°C – 1220º C) but will be paler at lower temperatures. So, be aware that the colour after bisque-firing is no real indicator of the finished colour, which, in turn, will be slightly different depending on whether it is glazed or not.
Body stains can be expensive, so buy small quantities to begin with, and test with and without glaze.
Dark colours require less stain – light colours need more.
Blacks, dark blues and greens – add 5% – 8%.
Yellows, pinks, mauves, 12% – 20%.
For example, if you wanted a 10% addition of stain you would add 10g to 100g of clay.
It really doesn’t matter if you’re adding these proportions to wet or dry clay, but you must be consistent and meticulous in your measurement and working practice for repeats.
KEEP RECORDS and label everything you make, in both the green state and fired.
You might find it useful to mix a batch of colours to a darker colour than you need, you can tone down the colour by kneading in more white to create varying delicate shades as you need them. Weighing, measuring and recording again are key for the success of this, and if you find you like this way of working and want to pursue it, it is easier to store one bag of deeply coloured clay than lots of bags in varying shades of the same.
BE AWARE that some colours and oxides will flux the clay (reduce the firing temperature) at high temperatures, so fire the tests on alumina to prevent them melting onto the kiln shelf.
Choosing the clay:
You will need to choose a clay to meet the working properties you need. For hand-building it’s preferable to have some tooth in the clay, so a textured/grogged clay is best, but throwers will need a finer clay. Your supplier will have a wide range of clays to choose from, but you’ll find the colour response is best if the clay is white, or at least pale-firing.
Colour response will be more vibrant in higher-firing clays and subtle in earthenwares.
Wearing a dust mask and latex gloves, begin by weighing out your clay and stain following the guidelines above.
Weigh the stain in a small container as shown.
Drizzle a small drop of water into the stain and mix thoroughly. If the stain was lumpy before adding the water, grind it in a pestle and mortar. If it’s still lumpy after adding water, put the mixture through an 80-mesh sieve.
Mixing with hot water might help.
Cut your weighed clay into slabs using a cutting wire.
Work on a large sheet of plastic, because things are going to get messy!
Spread some colour over the first slab using a spatula or spoon, then place a second slab over it and repeat until all the slabs have been piled up.
You may have to mix in the colour in stages, so don’t worry if you have some left in the container when all the clay has been stacked up.
Start to wedge and knead the colour into the clay – there’s no easy way to do this you will just have to get stuck in. It can look a bit like a murder scene when mixing reds and crimsons, but it is all the more fun for it.
Once the colour stops oozing and begins to mix into the clay take a more practised approach to kneading to avoid introducing air into the body.
Then if all the stain has not been mixed in, cut the clay into slabs again and repeat the process until all is used up.
If, when you have mixed in all the stain, you decide the colour is too dark, and you would like a lighter shade, weigh an amount of the coloured clay and an amount of white clay. Record the weights, then knead the two together. You can do this several times to make varying shades of the same colour. LABEL the bags you store each mixture in – accurate recording is essential for repeats.
The colour is thoroughly mixed when you can see no specks or streaks in the clay. Keep kneading until you get to this stage.
Clean up your workspace thoroughly, and repeat the process to make as many colours as you want.
Cut and weigh the coloured clays into small, equally-sized blocks.
In an ideal world, you would test each of these colours before continuing to mix them, and this is what I would recommend. However, knowing how impatient most of us are for results, we will continue the project in the hope that the outcome will be favourable without testing first!
At this stage, you have the option to use the colours as they are, to make a randomly colourful slab. Simply form small amounts of clay into balls and press them onto a sheet of plastic or cotton sheeting in a pleasing arrangement so that they overlap a little. When happy with the arrangement, roll out the clay to your required thickness, then cut out and use as you choose. The dishes shown here were formed using moulds.
With a selection of three to five colours, one being white, roll each sample into a square on a sheet of plastic. Use roller guides in any thickness you choose for this, and clean the rolling pin after each colour has been rolled before starting on the next.
When all the colours have been rolled to roughly the same dimensions, stack them up on top of one another in your chosen order.
Using either a long knife or your cutting wire, carefully cut through the stacked colours to divide the block in half.
Lift one cut half and turn it around so that the cut face matches the cut face of the section below it. Fit the two sections together, patting them down gently to ensure they sit together neatly.
Repeat the exercise, cutting through the block again, turning it around and positioning it on top of the laminated slab.
At this stage you have the option to work with your clay in this laminated form – you could cut it as it is, and reform the sections into a pattern, or you can work more loosely, as shown here, by carefully forming the stacked layers into a thick coil by rolling it gently.
Once the clay has been rolled into a thick coil, twist it as shown until a spiral pattern begins to emerge. You can do this a little, or really exaggerate the twist.
Cut the coil into thick sections – large enough to roll into small rounds to make shallow dishes. You can cut the sections with a knife or a cutting wire.
Place one section of clay on a plastic sheet or cotton cloth, and tap out the shape slightly with the side of the rolling pin to thin it. This is easier than trying to roll a lump of clay like this directly.
Roll the clay into a circle, turning it regularly to ensure it is round. Use roller guides to begin with, but if you want to roll it thinner than any guides you have, you will have to finish it by eye.
Cut out a shape of your choice using a template of some kind to cut around. Use a sharp knife for a clean cut around the edge.
Don’t waste any of the spare clay after cutting the shape out, simply roll it into a ball and store it in plastic until you have more to add to it, then you can roll this into a slab to make an interesting agate-like dish in the same way.
Turn the cut shape over and onto a hump mould to form a simple dish. Allow the clay to firm up considerably before attempting to do anything more with it.
An alternative method:
Cut a series of thinner sections from your twisted coil.
On a sheet of cotton, lay the sections side by side in a pleasing arrangement, so that they overlap slightly.
Use two roller guides, as shown, to work to a particular shape and contain the slabs.
Fill in any open spaces with smaller, cut down sections of the slabs or small amounts of plain, coloured clay.
Place a second cotton cloth over the top of the arrangement, then roll the shapes into a slab using the roller guides for an even section.
If you want to roll the slab thinner without guides, remove the covering cloth so you can see what you are doing, and roll by eye, as before.
Cut the slab to your preferred shape using a template if possible. If cutting straight lines, use the side of a roller guide for extra security when cutting.
Drape the second slab either over or inside a mould to form a second simple dish.
When your dishes have firmed up to a point where they won’t distort when handled, very carefully scrape back the surface using a metal kidney or scraper to more clearly reveal the patterning and colours in the clay.
If you’re too nervous to do this, you can fire the dishes to a low bisque – preferably supported on a bed of alumina – then sand the surface to reveal the patterning more clearly and create a more refined finish.
This project first appeared in issue 13. To buy the magazine, click here
For more projects, click here