Adding Stains To Glazes and Slips
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A small percentage of a stain (1 to 10%) can be added to a transparent or opacified glaze (a white glaze) to make coloured glazes. In the making of a slip, we would recommend using a ball clay called Hyplas71. The more stain added the more intense the colour but don’t add more than you need, as that increases the risks to health and safety. See our example photographs and suggestions. It is very important to test with your chosen host glaze as some glazes might not be compatible or they can affect the colour.
We have used these stains using our Vitraglaze range of transparent and zircon based whites.
Method:
We would suggest making a small amount and testing it with your chosen clay body. Applying it to a white clay will produce the brightest colour.
A simple way to test, use 100 grams of your chosen glaze as a powder, add the percentage of stain dependant on strength (see our recommended percentages for each colour). For example, for a pale yellow we would add 2% which is 2g and add 75g of water. You can sieve this in a 60# or 80# mesh test sieve but as our test was so small, we didn't sieve. For bigger quantities we would highly recommend sieving your mixture. Once you’ve mixed your test amount you can dip a small clay sample, re-dip 2 to 3 times and fire to the temperature of the glaze you are using. Increase the percentage of stain. We used for the majority 2%, 4%, 6%, 8% but some stronger colours, dark blue and dark green we used .5%, 1%, 3%, 5% and repeat the above. Don’t forget to label your swatch with an underglaze pencil.
For some colours indicated we have used stain enhancer at 2% (2g for the test) of the dry weight of the powder. This improved micro bubbling in the glaze and colours seemed brighter too.
If you wish to be more scientific in your testing follow the digitalfire document for a more organised and precise method.
In a decorating slip, we had success with the stain added to the ball clay (hyplas71) and mixed with water. This was then put onto dry greenware, fired to bisque and then glazed fired with a shiny transparent, to bring out the colour.
Making Coloured Clays
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You might want to make a clay a certain colour and this is possible with stains. But note, some colours may affect the way a glaze works with the clay body. Blue stains have a modified cobalt in them which can affect the melt temperature of the clay and glaze. Using white body clays will be the best choice but many advocate porcelain.
Method:
A stain can be added to wet or dried clay. The later will provide a more even colouring. Dry the clay out by putting small lumps on a plaster batt, then crush it in a bag with a rolling pin. Mix a percentage of the stain into the powdered clay but do not crush the stain. For a test amount you can take 10 grams of dry clay, add the percentage of stain that you want to test and mix them. Add small amounts of water to get a plastic consistency, then mix the clay in your hands into a workable putty. Make sure you protect your shelves and kiln.
For advice on mixing stains with wet clay follow this article from
The Pottery Wheel.
You could try colouring casting slips using our
white earthenware and
white stoneware, test as above, although you will need larger quantities for example 1kg slip powder and a small test mould.
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Using Stains As An Underglaze
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When using a stain as an underglaze you would need the addition of a flux. We have called it ‘underglaze frit’. We suggest a ratio of 4 parts stain to 1 part flux. Using a medium called ‘
Vitraglaze Mixing Medium - Pehatine’, it will give an opaque flat colour, if used with just water it will give a washed affect. Traditionally underglazes were painted onto bisqueware then overpainted with a shiny transparent glaze and then fired once more. It can be left without a glaze for a matt finish.
Having tested the colours with the ‘Pehatine’, the painting experience was better than any other premade underglaze we have ever used.
Method:
We used a stainless-steel bowl, put in 4.8g of stain and then added 1.2g of the underglaze frit powder. We then used a dry mixing brush to mix it thoroughly. We then used the equivalent amount in volume (a teaspoon) of the ‘pehatine’ neat from the bottle, then mixed it up using a medium firm brush. If you are making a significant quantity, you should then sieve with a 100# but with this small amount in a bowl we can see any agglomerated powder. You will see and feel how creamy and smooth this underglaze is, but do not be tempted to overpaint and build up layers however nice the experience. As a too thick underglaze with a glaze can impede the breathing of the clay in the firing process.
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Hand Painting With A Stain Onto An Unfired Glazed Surface
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If you have glazed a pot but not yet fired it, you can paint on that surface with a stain. We have tested a stain with just water, a stain with neat pehatine and finally a stain with the underglaze frit and pehatine (essentially an underglaze). All of these onto a buff clay body, pre-fired to a bisque of 999°C, with a Vitraglaze Tin White Speckle brush-on glaze, applied a little time before. This was then fired to 1240°C on a fast climb.
