burnishing pottery with a plastic bag

Burnishing Pottery With A Plastic Bag – Not That Strange!

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You may have heard of or even seen potters burnishing pottery with a plastic bag.  Perhaps this left you wondering what on earth was going on.  But the results of this technique can be quite stunning.  As ever, in pottery, there is more than one way to do something.  Here is some information about the different ways of using a plastic bag to burnish your pottery.

One option is to burnish the pottery with an object like a pebble.  Then the burnished surface is polished with the plastic bag.  Alternatively, the bag can be used to polish the pot after an application of terra sigillata.  This can be done by hand or on the potter’s wheel. 

Burnishing pottery has been around for a long time.  In fact, before glazing had been invented, potters would burnish clay to give it a shine.  And, although burnishing does not make clay waterproof, it does make it at least a little water-resistant.

Burnishing is an ancient practice with a history steeped in primitive pottery techniques.  The idea that the humble modern-day plastic bag might be part of that process can seem surprising.  But it is true.  Pottery techniques evolve, and it has been found that a plastic bag can give burnished clay a very high sheen.  Let’s have a look at how this is done…

Technically using a plastic bag to create a shine on your pottery is polishing rather than burnishing.  Burnishing in its true sense involves using a hard, smooth object on a clay surface to create a shine. 

Obviously, a plastic bag is soft, and therefore, strictly speaking, you are polishing with the bag.  Never the less, it is often cited as being part of the burnishing practice.  And there are different ways that a plastic bag can be used in that process. 

Here are Some Options:

  • Using a plastic bag to polish pottery after burnishing with a stone, spoon or another hard implement
  • Using the bag to polish your pottery by hand after applying terra sigillata
  • Polishing your pottery with a plastic bag on the potter’s wheel, having applied terra sigillata

Let’s look in a little more detail at each of these approaches.

Using a Plastic Bag After Using a Burnishing Tool

It seems that there are as many different ways of burnishing pottery as there are potters.  Most potters have their own individual preferences when it comes to burnishing. 

One of the differences in approach is the point at which you burnish your clay.  How wet/dry should your clay be when you burnish?  Well, the answer to that question is a matter of preference.  Basically, you can burnish your pottery in at any of the following times:

  • When the clay is not quite leather hard / still a little soft
  • Leather hard clay
  • Clay that is just past leather hard – when it is dark and almost bone dry
  • Bone dry clay

I’ve even heard of potters burnishing bisque fired pottery, though I’m not quite sure how that would work. 

I’m not going to go into an account of how to burnish clay in each of the above states.  Potter’s will adapt their approach a little depending on how wet/dry, hard/soft the clay is.  However, probably the most common way to burnish is when the clay is leather hard.

Because burnishing leather hard clay is the most common, I will refer to this method.  But be aware that you will probably find accounts that are different depending on the potter’s preference.

Image by Pat Joyce.  ‘Twisted Form‘.  Some rights reserved.  (CC BY-NC 2.0)

Sanding Before Burnishing?

The other difference that you may come across is that some potters recommend sanding their ware before burnishing.  You are more likely to come across this recommendation if the potter you’re talking to is burnishing bone dry clay.  However, it’s often said that sanding pottery leaves a dusty powder on the surface which can be hard to get rid of.

The main reason that potter’s sand bone dry clay before burnishing is to get a very smooth surface.  Getting a smooth surface is important, because it’s hard to burnish textured or uneven surfaces. 

However, there are other ways of getting a smooth surface.  One of the ways of doing this is to use a rib tool when you have finished throwing a pot.  You can also smooth out the surface when you are trimming your pottery. 

Burnishing Leather Hard Pottery

Burnishing is done with a hard implement.  This can be a smooth stone, the back of a spoon, or something similar.  Some potters even burnish with a small lightbulb.  The key thing is that the object has a smooth surface that won’t scratch your pottery.

Again, there are different approaches to the mechanics of burnishing.  However, a popular technique is to rub back and forth, switching direction frequently.  If you keep rubbing back and forth in the same direction, you will get lines on your pottery.  When you change direction frequently, this does not happen. 

The principle behind burnishing is that the clay platelets are flattened and aligned to form a smooth reflective surface.  As you rub, the clay particles become compacted and the remaining moisture in the clay is drawn to the surface.  Therefore, the clay becomes darker as you work.

Some potters will moisten the clay with a small amount of water as they go along.  Others will add oil, lard or even Vaseline to lubricate the surface and create a sheen. 

Burnishing even a small pot can take a long time (hours!).  Once you have finished burnishing, then you can polish the burnished surface with a plastic bag.

There are a few ways you can do this.  Firstly, the best kind of plastic bag, is the crinkly kind that you get from a grocery store.  The thick viscous kind from a department store won’t work.  It needs to be relatively thin and crinkly. 

Options:

  • Hold the bag in your hand and rub the pottery as if you are using a cloth or duster.
  • Wrap the plastic bag around the tip of your finger and polish using your fingertip.
  • Carefully wrap a piece of the plastic around a small sponge and use this to rub the pottery surface.

Any of these methods can be used.  Personally, I have found wrapping the plastic around the fingertip to be easier.  It gives a greater degree of control and accuracy.  You can feel the surface of the pottery and you know if you are pressing too hard. 

This is an important point when burnishing and polishing.  You do need to use enough pressure to smooth out the clay.  However, you also need to be careful not to press hard enough to break or crush the pottery.         

Brooklyn Museum / CC BY

Burnishing Pottery With a Plastic Bag Using Terra Sigillata

Terra Sigillata is consists of clay particles suspended in water, along with a deflocculant. It is basically a refined slip. 

Clay powder is mixed with water.  A small amount of deflocculant is added.  Deflocculants are chemicals which when added to slip causes the clay particles to repel one another.  This helps the clay particles in the slip to separate out. 

In practice, the larger courser clay particles settle at the bottom of the container.  The finer particles can then be siphoned off and used as a refined slip.  Once the refined slip has been siphoned off, it is concentrated down through a gentle heating process.  This thickens up the slip. 

Terra sigillata (or terra sig as its often called) can then be painted onto the pottery.  If it has been made well, it will immediately create a bit of a sheen on the pottery.  However, if it is then polished it can create a very high sheen. 

Like so many things in pottery, there are different approaches to using terra sig.  Some potters prefer to apply it to leather hard clay.  Others prefer to use it on bone dry clay that has been sanded. 

One reason for using it on bone dry clay is that leather hard clay does shrink a little.  The result can be that sheen on terra sig becomes dull.  This is because when the clay shrinks it causes the terra sig to become textured at a microscopic level.

Never the less, may potters do apply terra sig to leather hard clay and it can produce lovely results.

What About The Plastic Bag?

So, where does a humble old plastic bag fit into this picture?  Basically, once the terra sig has been applied to the pottery and allowed to dry.  The potter can use the plastic bag a little like a polishing rag.  There are two ways of doing this:

  1. Hold the pot in your lap or hands and polish the pottery as you would a treasure shoe!
  2. Position the pottery on the potter’s wheel, and hold the bag to the surface of the pot.  As the wheel head spins, the pot slips over the bag surface and this creates a high sheen.  A handy way to keep your pottery centered on the wheel whilst you polish is the Giffin Grip.

Final Thoughts

If you are feeling dubious about burnishing pottery with a plastic bag, give it a go and see for yourself.  Burnished pottery is, to my mind, one of the most beautiful finishes you can achieve.  Not bad results from the back of a spoon and a plastic bag!

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Pottery Tips from the Pottery Wheel

Lesley

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Pottery Tips from the Pottery Wheel

I’m Lesley Milne, the creator of The Pottery Wheel.  Like many people, I used the potter’s wheel at school.  But then I began to focus on clay sculpture and I left the wheel behind.  However, more recently, I found myself being drawn back to pottery and the potters wheel.  And so, I have tried to pick up where I left off all those years ago at school. This blog is a chronicle of what I have learned as I got back into the potters saddle!

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