DECORATING BONE CHINA

To many people this is the most important part of making bone china. Decoration comes in many forms to suit the different tastes of people around the world.

Artisits who are expert in the use of pattern and colour first design the decoration which can be applied either before the ware is glazed, under-glaze decoration, or after glazing, onglaze decoration. On-glaze decoration is by far the most common because the range of colours that can be echieved is larger.

FREEHAND PAINTING

Before 1790 all the decoration on china was hand-painted but, today, it is only used for the very highest quality china.

Freehand painting is one of the most skilled jobs in the pottery industry and it takes years of training to become expert.

GROUNDLAYING

The ware is coated with a thin film of oil and powdred colour is dusted over it. When fired, a very rich and rich solid background colour is obtained.

PRINTING

This is transfer decoration using a single colour. First a copper plate or cylinder is engraved and colou mixed with oil is spread over it. A transfer is taken on specially prepared tissue paper which is rubbed down onto the ware. The tissue paper is soaked off with water and the pattern is left. Prints are sometimes enriched by filing in the pattern with ceramic colors. In the industry this is known as ‘print and tint’.

LITHOGRAPHY

Lithographs are transfers. They are printed on a paper base and covered in a plastic layer. When soaked in water, the plastic and the colors can be slid off and onto the ware. They are then carefully squeezed down to remove any bubbles of air that are trapped underneath. This is by far the most common way of decorating bone china.

GILDING

Gold or platinum is often used to decorate bone china. The precious metal comes in liquid form and is usually applied by hands as lines and bands around rims and handles. Ornatepatterns can be applied with a rubber stamp. There are also specialist kinds of gold decoration:

Acid-gold is when a pattern is etched into the ware with hydroflouric acid then covered with gold to produce a pattern in relief.

Raised-gold is achieved by painting the pattern with enamel paaste and then covering this with gold to give the raised effect.

HOW BONE CHINA IS MADE:

The designer, the scientist, the hand-painter and the computer operator are just some of the people needed to make bone fine bone china.
What is Bone China is Made of?

25% China Clay:

Known as Kaolin, this is a very white clay which comes from Cornwall.

25% China Stone:

White granite stone made-up of quartz, felspar and micawhich also comes from Cornwall.

50% Bone Ash or Hydroxyapatite:

THis has been calcined at 1100C to produce a mineral and then ground to a fine power. It makes bone china very strong and translucent (which means that light can shine through it).

HOW BONE CHINA IS MADE

In the past of the work involved in making bone china was done by hand. Today, the potter is helped by modern machinary. Clay can be shaped automatically and modern kilns fire the china in minutes rather than hours or days. Potters used to work by trial and error but now scientists and techniciansmake sure that each piece is as perfect as possible.

Today, the designer, the scientist, the figure painter and the computer operator are just a few people needed to make fine bone china.

MIXING THE INGREDIENTS

In many ways, making bone china is like baking a cake. The ingredients are mixed together, a shape is formed, it is baked in an oven and, finally, decorated. As with a cake, a mistake at any stage will spoil the finished piece and every process involved in making bone china calls for experience and skill.

1. All the ingredients are individually mixed and then blended together with a precise amount of water in a tank called a blunger until a creamy liquid clay is produced. This is called ’slip’.

2. The slip is sieved and then pumped over powerful electromagnes to remove particles of iron which would cause dark spots to appear on the finished china.

3. It is pumped into nylon filter bags which are hung in a long row on a machine called a filter press. This squeezes out the excess water to form slabs of clay which feel rather like plasticine and now contain about 23% water.

4. Finally, the clay goes through a pug mill which is rather like a giant mincing machine. It thoroughly kneads the clay and a vacuum pump removes air bubbles that would cause the clay to crack in the kiln. The clay leaves the mill as long sausages which are now ready for the potter to shape.

DESIGNING

Before anything can be made someone has to decide what shape the pieces are to be. This is the job of the designer who must make sure that they are practical to use and, of course, beautiful to look at.

MODELLING

Using the designer’s drawings, a plaster or clay model is madefor each piece. From these, identical palster-of-paris moulds are taken which are used to make the china. These moulds are always larger than the finished piece will be because the clay will shrink when being fired in the kiln.

SHAPING THE CLAY

The potter calls the things he makes ware. Plates and saucers he calls flatware and cups, teapots and jugs holloware.

1. Flatware is made by forming a pancake of clay, a ‘bat’, on a revolving disc which is thrown onto a plaster mould. The mould shapes the front of the plate and a metal profile-tool is lowered to form the back. This process is known as jiggering and can be done by hand or by automatic machines.

2. Holloware is made by throwing a ball of clay into a revovling mould and lowering a profile-tool to form the inside shape of the cup or dish. As the clay is pressed against the mould the outside shape is made. This is called jolleying. Handles are stuck on later.

Many things like teapots, jugs, bowls and sometimes, cups are too complicated to be made by the jolleying machine. These are made by casting in plaster-of-paris moulds. Specially prepared slip is poured into the mould and the porous plaster absorbs water from it to form a layer of set clay which gets thicker and longer it is left. When it is thick enough the slip that is left is poured away leaving a clay shape on th einside of the mould. Often things are cast in a number of pieces and later stuck together with slip.

When the ware is dry enough it is carefully trimmed to remove any excess clay and the surfaceis made perfectly smooth with a damp sponge. This is called fettling and sponging. The ware is now ready to be fired for the first time.

BISCUIT FIRING

Bone china is fired at a temperature of around 1,200 degreed C. which is hot enough to bond all the ingredients together and make the clay hard, strong and translucent. During firing, the high temperatures make the clay soft and great care must be taken to make sure that the pieces do not lose their shape. The ware is stacked onto truncks in a special way to avoid this.

All the water in the clay is driven out during firing and so the pieces shrink by about 13%. They leave the kiln feeling dry and biscuity-hence the name of the process. After being brushed and inspected for any faults they are ready to be glazed.

GLAZING

The glaze on a peice of china is really a very thin coating of glass used to make the pieces perfectly smooth and attractive. Glaze can be colourless or coloured, opaque or transparent and each is made to a very precise formula. It is applied by either dipping by hand into a tub of glaze or by automatic spraying. After drying the ware must be fired again.

GLOST FIRING:

Making sure that the peices do not touch each other, the ware is again loaded onto trucks for a glost firing at a temperature of around 1080 degrees C. This turns the glaze into a brilliant glass coating and fixes it firmly to the piece. After another inspection the china goes to be decorated.

DECORATION:

There are many ways to decorate bone china but the most popular are with enamel colors and precious metals. These and other kinds of decoration are described in the seperate section.

ENAMEL FIRING:

Ball Clay:

A very plastic clay mined in Devon and Dorset. So named because it was originally mined as lumps or balls weighing about 14kg.

Biscuit Ware:

Also called bisque ware. It is pottery that has been fired but not glazed.

Blunger:

A lareg vat in which rawe materials in both liquid and solid form are mixed together.

Bone China:

The English form of porcelain. It is white, translucent and very strong. The key ingredient is bone ash.

China:

In Britain, this usually refers to bone china but is sometimes used to mean all forms of porcelain. So named because the Chinese were the first to make it.

China Clay:

Derived from feldspar, it is the purest form of natural clay. It has a fine texture and, when fired, burns very white. In England it is mined in Cornwall.

China Stone:

Also called Cornish Stone. It is feldspar less decomposed than china clay and is used as a flux.

Clay:

The essential raw material for ceramics. It is foundin many forms practically everywhere in the world. It is formed when rock breaks down under the action of the weather or by chemical processes- as in the case of china clay.

Earthenware:

Pottery fired at a relatively low temperature. This means that, unlike china, it is not vitrified but is porous, opaque and not so strong. It must be glazed if it holds liquids.

Enamelling:

Enamel colours are metallic oxides fround to a fine powder with a flux added. Fired at a low temperature, it is used to decorate pottery that has already been glazed.

Enamel Firing:

A low temperature firing given to ware decorated on-glaze.

Faience:

A French term for any porous pottery body.

Feldspar:

An ingredient of clays.

Filter Press:

A press used to extract water from slip.

Firing:

Baking ware in a kiln.

Flatware:

Ware such as plates and saucers.

Flint:

Ground flint is mixed with some pottery bodies to control expansion in the kiln.

Gilding:

Using gold or platinum to decorate china.

Glazes:

A thin coating of liuid gass applied to most ware.

Gloss-firing:

The firing given to ware after glazing

Holloware:

Ware such as cups, teapotsand vegetable dishes.

Jiggering:

Shaping flatware such as plates with a machine called a jigger. A pancake of clay is sandwiched between a revovling plaster mould (which forms the front of the plate) and a metalprofile-tool (which forms the back).

Jolleying:

The same principle as jiggering applied to cups- the mould forms the outside and the profile-tool the inside.

Kaolin:

Another name for china clay.

Kilns:

Heated chambers used for baking ware. They vary greatly in size, in the way they operateand the fuel they use. The two main types are ‘intermittent’ and ‘tunnel’ kilns.

Lithographs:

Transfers used to decorate ware.

Moulds:

Normally made of plaster of paris and used extensively for shaping both plastic and liquid clay.

On-glaze:

Decoration of ware after the glaze has been fired.

Porcelain:

The general term for a vitrified, white nd translucent material. In Britain, it normally refers to ware made from a feldspathic body and is thus distinguishe from bone china.

Pug mill:

Rather like as giant mincing machine. It kneads the clay to emove all bbubbles of air and give it an even consistency.

Refractories:

Materials which can wihstand very high temperatures. Fireclay is an example.

Slip:

Clay and water mixed to a creamy consistency. Slip is made as a means of accurately mixing the ingredientsof a pottery body (in which case it is then filter-pressed) or to be used for casting ware in plaster moulds.

Slip casting:

Casting with liquid clay.

Stoneware:

A vitreous but opaque pottery body.

Throwing:

A method of shaping holloware. A ball of clay is thrown onto a revolvong potter’s wheel, is centred and then shaped by the hands.

Under-glaze:

Decoration of ware before glazing.

Vitrification:

When clay is fired one of the constituents-silica-is changed into glass and bonds all the other ingredients together. As vitrification proceeds the proportion of glassy bond increases and its porosity becomes lower. China is fully vitrified.

[tags]porcelain, ceramics, dinnerware[/tags]