Burnish pottery is a method that consists of polishing the surface of the piece until it shines without using glazes.
In the past, potters used this ceramic technique because they had no other option to produce pieces with smooth and shiny surfaces, since the chemical materials that can be found today and that are part of glazes and varnishes were not available.
Bowls in brown chamotte clay and burnished with jade stone.
By Dureza de Cuero Cerámica
WHAT IS POTTERY BURNISHING USED FOR?
The burnishing technique is used to produce a remarkable and beautiful gloss effect on ceramic pieces.
Because it closes the pores, the surface will have a better waterproofing.
With this method we will achieve a very good smoothness on the outer face of our works and a texture more pleasant to the touch.
In addition, we will save having to use a layer of glaze on our work.
WHEN IS BURNISHING APPLIED TO CERAMICS?
This technique is recommended when the piece has the so-called “leather-hard” (so called because it has the feel of soft leather). This is a suitable point between the wet piece (which can be easily deformed) and the dry piece (which is brittle). It must be said that the surfaces can be burnished in this dry state, however, it will be appropriate to moisten them to be able to work them well.
Very well preserved burnished piece of Egyptian art (3000 BC).
Metropolitan Museum of Art
WHAT TOOLS ARE USED TO BURNISH POTTERY
Burnishing is an ancient technique and does not require sophisticated tools; it can be done simply with the ceramist’s own hands and a stone; wood, bones, etc. can also be used. Although we always have the option of using industrial elements and machinery.
The stones for burnishing ceramics must have a suitable smooth surface, a very commonly used stone is the agate stone (which is also very often used to achieve the characteristic shine in gold leaf), although there are ceramists who use simple river stones.
HOW TO BURNISH POTTERY
The technique of burnishing in ceramics is not very complex to execute. As we said, it can be done manually using a stone that meets the appropriate characteristics or using machinery. To achieve a perfectly burnished surface, the surface should not have too many reliefs, so that the stone or the element that we use to burnish can reach all of it, if we could not reach some areas because they are concave, they will stand out for their greater roughness.
Before starting to burnish it is necessary to have something to moisten the surface such as a cloth dipped in a container of water to which oil can also be added.
We will have to wet the piece if we already have it in a too dry state, for this we can help us with our fingers, spreading the water well over the entire surface before starting to use the stone. This will help us to make it easier to polish and will fill the tiny incisions that may be noticed.
The excess water can be spread with the cloth we have for this purpose.
This phase of abrasion of the surface has to be done in one step, always keeping the surface wet, avoiding intersection and separation areas as we work. Some people use a spiral pattern so that no delimitations are noticed (for example, if we are burnishing a ceramic vase, we will start at the top, i.e. the edge, and we will go down, making a spiral towards the base).
The reason for doing in one step is because once the piece is completely dry, if we reapply the tool with which we are working, marks or scratches will be noticed; that is why it is important to do it continuously and maintaining the necessary humidity on the surface.
Burnished ceramic piece by Chloé Van der Mije
FIRING BURNISHED POTTERY
It should be taken into account that when the piece comes out of the kiln, if it has been cooked at high temperatures, it may have lost the original shine it had before being cooked. In wood-fired kilns, this shine is preserved a little more, but it is also necessary to consider the smoking process.
With high temperatures we refer to more than one 1800º F, from that point on the achieved brightness can be lost, so we must take into account this limit when choosing the base clay with which we are going to do our work, that is to say, we will use one that does not require firing above that temperature.
You can see this video about burnishing pottery.