Techniques - ClayPrint this page

Techniques - Clay

  1. The equipment needed
  2. The skills and technical knowledge needed
  3. The stages of the process
  4. References

Preparing a structure

When the sculpture is big or with a vertical shape, it is important to create it around a structure which will support the clay and will avoid that it collapses during the work. The structure must be able to be removed before the cooking.

The structure can be constituted by a threaded steel rod inserted into a wooden board provided with wooden strips on the bottom to heighten it, the rod is fixed on both sides of the board with nuts and washers fixed well which maintain the stalk in position.

On the rod is then fixed a ball realized with plastic bags squeezed well around rod and fixed with a wire. It is necessary to make sure that this ball is maintained well on the rod because the clay will weigh on it. Also the volume of the ball and its position on the stalk will have to correspond to the volume of the sculpture so that the plastic does not risk to stand out during the work. The clay (a little bit hard) will be put on the plastic ball and the central stalk.

When the shape of the sculpture requires it, the central rod can maintain an arm which will support the clay. Furthermore, wooden baguettes or strips can be added to maintain parts of the sculpture which would risk to collapse. The important is that all the elements can be removed before the cooking. In order that the clay doesn't split because of its retraction which will not happens to the elements of support, it is interesting to stick a little bit of clay of the same consistency as the sculpture on both sides of each of the elements of support, so their size will decrease at the same time as the sculpture and will avoid the appearance of tensions.

Creating the volumes

Put the clay on the structure to form the volume which will be necessary for the sculpture by pressing well the clay on the plastic ball and the rod so that it does not slide. It is interesting to use at this moment not too fresh clay so that it does not slide along the structure, during the work later you can work with fresher clay because it is easier to model. The objective of this stage is to realize a global volume and especially not to realize details, it is necessary to make sure in particular to position the good volumes at the right place.

Realizing the sculpture

Once the volumes are correctly set up, you can begin to realize the sculpture. It is important to proceed step by step, without rushing directly to the details, even if it is attractive, by placing first of all the volumes and the elements correctly. Indeed the clay will dry throughout the work and it is a problem to have to proceed to important modifications while the clay is already hard, the mistreated clay will break or will split. Furthermore, a clay a little bit dry facilitates the realization of details.

For example, to realize of a foot, we shall place in a global way the volumes of the ankle, of the heel, the kick and the toes without realizing details and it is only when these volumes will be correct that we can proceed to the realization of details as the separation of toes. In the same way when we realize a head, the most frequent error is to work the elements of the face without taking time to set up the volumes of the head in particular the skull which represents an important volume, the zygomatic arch and the jaw. It leads to big errors of proportions which, if details are realized, will be complicated to repair afterward because details will probably have to be completely begun again to obtain a realistic result.

Opening a sculpture

It is sometimes essential to open the sculpture to remove the structure from it or to empty it. We proceed to the opening, according to its location, with a knife (handy to cut) or a cutting wire (the cut is finer). The opening must be big enough so that we can proceed to the desired operation (taking off the structure or emptying) without damaging the sculpture, but it is important to avoid to cut places with details or texture because these would be to redo then. It is necessary to choose carefully the place of the opening. So for a head, we cut off the back of the skull with the wire to empty the inside of the skull, then we shall restick it and turn the sculpture to empty the neck and the shoulders by the bottom taking care to join both zones emptied inside the neck. For a body, we shall open the back or the stomach with a knife by practising two sections in the shape of diamond. We shall avoid damaging possible details as hands by choosing the zone where there is least details or texture, then we can empty the head and the thighs taking care to join the emptied zones.

Taking off the structure

Once the sculpture is almost finished and the clay is a little hardened, it is necessary to take the structure off the sculpture. This stage must be realized at the right time, because if the clay is too soft the sculpture risks to collapse, but if it is too hard the risk is not to be able to remove the structure.

If the structure is only a rod, you can take the sculpture out through the top by turning it slightly to remove it from the rod. Attention to maintain the balance of the sculpture so that it does not fall. You can then either put the sculpture back on the rod while ending the work, or put it against the rod, attached to it with a rolled plastic bag (it does not leave marks on the clay).

If the sculpture contains a ball of plastic (or pieces to maintain it), it will be necessary durong the work to open it to take the plastic out of it, the cut must be big enough access easily to the plastic. Cut the wire first everywhere you can access it with a wire cutter, then with a cutter cut the ball of plastic and remove it piece by piece. Then close the sculpture around the rod and continue to work. Watch out, it is not the moment to empty because the sculpture would become then too fragile to be worked on, it's just for removing the plastic and closing, you will empty the sculpture later when the clay will be harder.

Emptying the sculpture

Once the sculpture is globally ended, it must be emptied to avoid any accident during the cooking (unless the sculpture is very small). Indeed if the sculpture is full, it multiplies the risks of presence of an air bubble in the clay which might cause the breakage of the sculpture.

The emptying of the sculpture is an operation which must be realized when the consistency of the clay is correct, not too wet to avoid risk of collapse nor too hard because the emptying would be too difficult. The correct consistency is leather. The emptying has to begin through the top to avoid the sculpture to collapse under the weight of the full parts. Never forget that the emptying of the sculpture leaves air inside the sculpture and that an opening has to allow it to escape during the cooking with a hole made on a hidden part or by leaving the bottom open, without forgetting to check that all the emptied parts communicate together to allow the circulation of the air.

Once the sculpture was emptied, it becomes fragile because the clay is thin, attention not to moisten it and to manipulate it carefully (especially in small parts as neck).

The emptying is generally made with a sharp trimming tool used to remove the clay, the objective is to leave an equal amount of clay all around the sculpture, what is not easy to do because of the volumes of the sculpture. We maintain generally a hand on the outside of the sculpture to feel with the hand the thickness and to know where to remove clay. Also empty the cutted part cut with the same thickness.

Closing the sculpture

To close the opening, scratch each part and apply generously clay slip on them. Then press carefully the parts on each other and mix the clay all along the cut. Then make thin clay coils to apply all along the cut to add the volume needed, and mix them with the clay to erase the cutting mark. Then you can redo the texture of the clay.

When emptying a head for example it is interesting to proceed to the emptying before doing the hair because the emptying will destroy it.

Cooking the sculpture

Before cooking the sculpture in a ceramics kiln, you have to make sure that it is totally dry, a wet clay will break into pieces during the cooking.

Skittles of different sizes
Skittles of different sizes

The sculptures to cook will be placed on kiln plates made in refractory material which rest on skittles (at least three by plate so that it is stable. For a kiln for biscuit (first cooking), objects can be in contact without risks or touch the walls of the kiln, what will not be the case for a kiln for enamel (second cooking) where it will be necessary to keep at least one centimeter of space around each object to avoid enamel projections and streaks. We try generally to fill as far as possible the oven and in a uniform way so that the heat circulates correctly. Attention however on piles in unstable equilibrium which risk to cause breakage during cooking.

The filling of an oven is a delicate and taking time stage, which demands peace and concentration to break no element of sometimes fragile sculptures and with sometimes difficult forms to fit.

The cooking has to respect the temperature of cooking indicated for the used clay. Attention with mixed clays of various natures because if their temperatures of cooking are not similar it can raise big problems and even break the oven.

 

 

The skills and technical knowledge needed Read more: The skills and technical knowledge needed

Read more: References References

 

 

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