celadon process





Raw materials: ball clay, kaolin(china clay),red clay,
wood ash, rice field surface clay, feldspar.

Clay forming: Throwing, Slip casting, Jigger and Jolly

Throwing
Hand-forming a mass of soft plastic clay on a rotating wheelhead is called throwing, the techique can
be traced back beyond 3000 BC. And still remain unaltered. Before the clay is used it must be prepared
to ensure it is of an even consistency, contain no air pockets of foreign bodies, and is in the appropriate
state of wetness or dryness for the technique that are to be employed. The potters use the method of
kneading combined with wedging the clay before put the ball shape on the center of the wheelhear.

Then the centering and shaping is done by steady pressure with the palm of the hand, open the clay by
using both thumbs and raising the clay into cylinder shape first and form the desired shape by the two palms then the item is removed from the wheelhead to let it dry to leather-hard and then the item is back to the wheelhead again to retouch the shape and form the foot rim of the ware.  This process called trimming, the piece must be recentered in an inverted position on the wheelhead
before turning can begin. It can then be carefully fixed to the wheelhead with small pieces of clay around rim.
The potter use shape metal tool to remove the layer by pare off in long strips.

Slip casting
This is a common industrial production technique. It is an efficient and low-cost method that enables us to create mass produced items that nevertheless maintain an individual character through their individual decoration. the slip is poured into a plaster mold of one or more pieces depending upon the complexity of the object.

Molds of two or more pieces are held together with elastic bands or string to prevent seperation when filled, and a thin layer of pliable clay is deposited evenly over the
wall of the mold. The porous plaster mold absorbs the water from the slip, so that the slip level drops gradually and needs to be refilled.

Any surplus is then poured out and the mold is left inverted to drain when it stops, it should be turned upright and left untill the deposited clay lining loses its shiny, wet surface.

Jigger and jolly
Ours pottery can be formed in rotating plaster molds with the use of a mechanical arm to which a metal-profiled template is attached. When the mold forms the inside shape and the profile the outer surface, the process is referred to as jiggering, while the reverse, with the mold forming the outside shape, is call jollying. In both processes, the molds fit into a cup wheelhead to hold them in place.

Jiggerig is normally used to form plates or shallow dishes . A slab of plastic clay is placed onto the convex shape of the mold, and while it rotates, the mechanical arm with its shaped metal profile is lowered onto it. The profile is lubricated with a little water and the arm is preset to be lowered only to the point at which the correct thickness of clays is achieved over the mold. Jollying is most frequently
employed in the production of the deep shapes such as cups or cylinders, the shapes being limited to those that can be ealily removed witout snagging in the mold.

A prepared lump of clay is placed in the bottom of the concave mold and can be roughly spread up the walls
by hand as the mold rotates. The jolly arm with the profile is then lowered into the mold to complete the spreading of the clay to from the requied internal shape and attain an even thickness.

Bisque Firing (Biscuit firing)
Bisque firing is the first stage, which transforms clay into permanent pottery. To minimise risk to the pottery,
all items are given sufficient time to be thoroughly dried out before firing. Where pieces of work are particularly thick, it has to be preheat the kiln to ensure that everything is as dry as possible Articles to be bisque fired could be packed into the kiln as closely as possible; items can be touch, rest each other, be placed inside each other, or be stacked rim to rim or foot rim to foot rim.

The initial stages of firing are the most critical as the "dry" clay still contains a high percentage of chemically combined water which turns to steam and must be allowed to escape slowly so that it does not force off sections from the walls of the pottery. The heat should be allowed to build up gradually inside the kiln untill a temperature of at least 800 degree celsius has been reached.

Glazing
There are many different glaze types and numerous glaze recipe. For our production, we have improved and develope thai ancient stone ware glaze to be more practical and easier for the preparation.

Ours glaze consist of the three main local natural materials which are quite hard to find. The first is the local northen thai nut tree's wood ash called " mai goor" the second is a layer on the top of the rice field clay surface that is relatively soft, but give excellent light jade green color response. The third is the high fine Feldspar powder.

The three materials has to be wet grided in the ball mill for approximately 8-10 hours then the mixture is magnatically pass through a sive of 100 mesh size.

Applying the glaze
Dipping is the best method for small pieces or pot, use thumb and forefinger to hold the vessel or pot, use thumb and forefinger to hold the vessel dip the vessel face down into the glaze hold for a few seconds and lift out shake off any drips. touch up any missed areas with a brush leave to dry and wipe off the foot ring(botton) of the ware thoroughly with a damp spoge. For quite big pieces spraying with a spray gun can produce very even layers. This should be done in a well ventilated area in a spray booth with appropriate extraction facilities.

Glaze firing
This, also known as glost firing , is normally a second firing of pottery after bisque firing and glazing, and it fuses the glaze to the pot. Pot should not come into contact with one another or it will stick together once the glaze melts. The temperature required is 1260 degree celsius for about 10 hours. There are two types of firing.

Oxidized Firing
The type of the atmosphere within a kiln during the firing will effect the appearance of the pots.

The firing atmosphere with sufficient oxygen to allow complete combustion and to combine with metals present in both clay and glaze. Because carbon dioxide gas is given off, this is described as an oxidizing atmosphere. Typical results from this type of firing , we achieve the yellow and
celadon ivory glaze appearance which are quite different to those obtained in reduction firing.

Reduction Firing
This is done in ours shuttle kilns fired by combustible LPG gas, where the supply of oxygen can be limited to prevent full combustion taking place. This will produce Cabon monoxide which, if hot enough, will take oxygen from the metals present in both clay an glaze and produce tolally different effects to those of an oxidized firing typical effects obtained by reduction firing are ours light jede green
called Celadon green, Celadon Navy blue, celadon white.

 
 
   
 
 

 

         
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