Keeping a good texture clay
When working on a sculpture in clay, the work can extend over a period which can be long. It is thus very important to keep a good working texture of the clay to avoid all the inconveniences which would ensue from a too fast drying (too dry clay, cracks, breakage).
It is also necessary to specify that the clay taken out of its packaging is generally very soft and can thus make the work complicated (collapse). It is thus interesting to have at disposal a little harder piece of clay which will be useful in particular for the implementation of the volumes.
Keeping its good texture to the clay passes first of all by good working techniques. So it is necessary to avoid mixing too much the clay because the palms of hands dry the clay and make it cracked. In the same way, to make from the beginning of the sculpture the fine details will increase the risk of too fast drying of these, we prefer to put thus generally at first the volumes to only get into detail then (what is always preferable in any case in sculpture).
Vaporizing some water
A spray filled with water is used to moisten the sculpture superficially to facilitate the work. Attention however not to moisten too much sculpture, what weakens it and increases the risk that the clay deforms under the influence of the gravity (arms of sculpture can collapse because of a too much moistened clay). To be good to work, the clay has to acquire a certain texture linked to the drying which will allow it to hold; if the sculpture is moistened too frequently, the sculpture will remain fragile, what is very risky for the work and for the emptying. The sculptor has to learn to realize his sculpture at the rythme of the drying by using in every stage at best the properties of it.
Using moistened strips
When a small part of the sculpture dries too much, it becomes useless to use the spray because its water evaporates too fast to be absorbed in depth by the clay. To moisten in depth a sculpture, or keep the humidity when leaving the sculpture for some time without working on it, it is interesting to use wet strips of cloths which will maintain the sculpture at a good level of humidity. Wrap up the parts of the sculpture too dry or susceptible to dry too fast (for example feet or hands of a character).
Attention especially to press well the strips to take water out of them before applying them on the sculpture to avoid that the clay becomes too soft and collapses. Strips have to be only slightly wet, what is sufficient to in-depth moisten the sculpture.
Packing the sculpture
Finally it is essential to be very careful in the way to keep the sculpture. It must be carefully packed as soon as the work is ended. To keep a texture allowing to pursue the work, it is necessary to pack it very carefully after every working day to avoid that it dries with the environnement air. An assortment of bags of various sizes is then interesting to pack the sculpture, whereas the link of the bag allows to close it carefully. The simplest is to use a big enough bag to be able to contain the sculpture and its working base, we then place both in the bag which we close at the top with the link. When the sculpture is too big for both, the sculpture can be covered with the bag which we close by sliding edges by means of a knife under the sculpture (when the base is continuous) or by using adhesive tape to stick it on the wood and make the bag hermetic. When the sculpture is very big, it is necessary to use several bags cutted and stuck to each others by means of adhesive tape (attention to keep well the plastic pieces and the tape so that they can be reused after each working session).
This stage must be realized with big care because the risk is that a badly packed sculpture cannot be afterward worked again because it will have become too dry. It is thus necessary to take time to cover the sculpture with plastic and to make sure of the waterproofness of this one. In the case of big sculptures it can turn out complicated because it will then be necessary to scotch-tape plastic bags some to the others to cover the whole sculpture by making sure that there is no space where the air can infiltrate, at the risk of accelerated drying!
Finally, once the sculpture is finished, it is interesting to cover it with a plastic bag not closed to provoke a slow drying which will avoid the appearance of cracks and will limit the retreat of the clay. This bag can be removed as soon as the drying has begun well.
Gluing with clay slip
If we speak generally about glue to name the slip, it is necessary to think that it is not really a glue. If you take both pieces of a sculpture, coat them with slip and press them one against the other, it will not work, as soon as the water of the slip will be absorbed by the drier clay of the sculpture, both pieces will get loose. It is thus necessary to interpenetrate carefully the clay of the two pieces by using the slip as a linking agent.
First scratch both side to stick, I mean really streak them profoundly with a knife. then apply above widely the barbotine and scratch again to assure a good penetration of the slip. Then press the both parts against each other and use a tool to mix the clay of both edges. Then you can add a little bit of fresh clay and mix it well with the slipped clay. Last step will consist in working again the damaged part to improve the appearance. Watch out, just after the sticking this part remains fragile, it is better to wait that it solidifies a little to work on it and avoid wetting it again.
If the sculpture is too dry to use slip, you can use alcohol vinegar with a brush to moisten the parts that has to be restuck (bubbles have to form and the clay begin to disintegrate) and then well mix edges to homogenize the clay of the parts.
Doing clay coils
Clay coils are an important element of the modelling of the clay, they allow the construction of an empty sculpture, they are used to realize elements of the sculpture) as arms, hair or eyelids and they allow to repair some problems (when we close the sculpture for example).
To realize a clay coil, take a piece of clay and roll it on a clean work plan. It is important to use your fingers and not the palm of your hand and to apply a uniform and not too important pressure to avoid deforming the coil. It is also necessary to roll it widely to avoid that angles appear. Finally the realization and the use of the coil must be fast so that they do not dry out in contact of the wood and the hand because then it would crack and become unusable.
If you need to use numerous coils, you can make them in the beginning of work and then keep them well covered with a plastic bag to avoid them to dry, attention because the smaller the coils are, the faster they dry!
The coil can be then applied to the sculpture, directly if both have the same consistency, with the barbotine if the sculpture is drier.
There are various types of ceramics kilns, mainly with wood, gas or electricity. There are two types of electric kilns: the ones with a front door and those with a top door (generally smaller, but adapted well to the ceramic objects).
Electric kilns are the easiest to use because they are safe (no gas) and provide advanced programming which allow, once the regulation established, to launch a cooking with only a few press on the command panel. However they present the defect to realize a cooking without subtlety through resistances and without flame nor release of smoke. Attention however because the resistances of these ovens are fragile.
The objective of these kilns is to allow to reach the temperatures of cooking of the clays which must be cooked (generally between 900 and 1200°C). Attention to avoid cooking in the same oven clays with different temperature of cooking, even during different cookings because there are very often small pieces of earth remaining in the oven. Yet the clay (cooking between 900 and 1000°C) is going to melt and to flow if it is cooked in temperature of cooking stoneware or porcelain (between 1200 and 1400°C) what risks to damage seriously the resistances of the electric oven.
Numerous ceramists prefer wood or gas kilns which by the presence of a flame give off smoke (and ashes and embers in the case of the wood kiln) allow to create effects on the sculpture and to realize processes of patina as the raku. Wood kiln also present the interest of being built around the sculpture, which is very interesting for large-sized sculpture. However these two types of kilns require the surveillance of the cooking which can last several days and the construction of a wood stove requires a good experience.
To know more about ovens and cookings, a very complete website which explains all the aspects (choice of the oven, material, filling, cooking curves): http://sitepasite.free.fr/poterie/index_cuisson.html