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Tuesday, 30 October 2012

Burnishing unfired clay pottery

Burnished ware by David Greenbaum
I recently came across the term 'beeswax pottery' and wondered what it meant. I discovered that it was a form of burnishing clay pottery to give it a smooth attractive mainly waterproof finish. Previously, to me, burnishing was just a term for the polishing of gold decoration used for the decoration of pottery.

It reminded me that you never stop learning with pottery. It is such a wide subject which continues to grow as new techniques are invented (or old ones re-invented!).

 History of clay burnishing 
Many ancient potters used burnishing to make their pottery harder and more waterproof before they discovered the use of glazes. Nowadays, modern potters choose to finish their work by burnishing because of the subtle, but beautiful finish achieved using this method. A burnished pot often has a soft, tactile quality all its own. However modern potters also need to know that this type of pottery should be used for decorative purposes only and not for ware intended for contact with food or drink.

Health and safety considerations are now a more important part of our modern life!

 So What is Burnishing and how is it done?
Burnishing is basically rubbing the surface of the clay piece until it becomes glossy. To achieve a satisfactory finish it often takes several hours for even a small pot. Skill and practice are required for this technique as it is highly influenced by the state of drying. The best stage to burnish is usually at the later stage of leatherhard. However many potters burnish the piece more than once to achieve the ultimate finish.

Working in very small areas, applying a little lubricant at a time to the piece, rubbing in different directions will gradually create a sheen. Care is needed as sufficient force is needed to compress the surface but not create a hole or flake. After firing the sheen is mostly retained and can be improved by polishing with beeswax or other types of wax.

 Some key factors to consider when using this technique include:-

  Choose your clay wisely
Burnishing requires either a very fine clay body, or fine clay engobe. Clay bodies which contains grog or sand are therefore not recommended for this technique. Low firing clay bodies such as earthenware are also recommended as higher firing bodies can give rough texture after firing.

Choose your shapes wisely
Pots with smooth flowing surfaces are easier to burnish and look so much better when fired. Complex shapes with sharp corners or surface features will be almost impossible to burnish properly.
  
Choose your tools wisely
The burnishing tools you use need to be smooth, hard and easy to hold. As burnishing is a very time consuming process comfort is an important factor and this is a personal thing. However most potters use the backs of spoons or polished stones for this technique. Some potters carry out a secondary burnish using smooth plastic or other materials.

Choose your burnishing oil wisely.
To aid the burnishing process the use of a burnishing lubricant is recommended. The lubricant allows the clay to densify and give an even smoother finish after firing. . Lubricants that are often used include vegetable oils, lard, and water. Although the choice of lubricant is subjective, water is the least recommended as there is a tendency for it to soak into the body or flake the surface as it is pressed.

Firing 
Firing of the ware after burnishing is important and can alter the texture of the surface significantly. Low firing clay bodies appear to work best.

 Post firing polishing 
 Firing gives the burnished ware a lovely, tactile soft feel. In ancient times, animal fat, oil, and wax were often used to make it more waterproof and to restore the pre-firing high gloss. Today, most potters use a  form of wax. Paraffin wax, candle wax, and beeswax, have all been used successfully. By applying the wax to a small area of heated ware and polishing a high sheen can be achieved.  The result is an outstanding piece of decorative ware that often looks as though it has been glazed but feels so different!

If you found this article of interest make sure you read about Terra Sigallata a method for making shiny ware without the polishing stages!

Of course 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.

3 comments:

  1. Hi,thanks for burnish advice. Am making sculpture-like pots, handbuilt, and I would like to use oil,but, as I burnish a few times over, can I use oil each part of process. Am bit scared that the oil could case complications in firing..not everything I have read has suggested this use.

    ReplyDelete
  2. Hi Lucinda, Thank you for your interesting question. As you rightly say the more oil you use the more likely you can have burnout issues. Unfortunately there are no hard and fast rules. However I would suggest you use lighter oils (which will fire away easier) and make sure you have a slow firing cycle to allow the oils to fire away easily. Hope this helps. The Potters Friend.

    ReplyDelete
  3. Hi Lucinda, Thank you for your interesting question. As you rightly say the more oil you use the more likely you can have burnout issues. Unfortunately there are no hard and fast rules. However I would suggest you use lighter oils (which will fire away easier) and make sure you have a slow firing cycle to allow the oils to fire away easily. Hope this helps. The Potters Friend.

    ReplyDelete

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