How the China is made
The name Bone China comes from its origins, here is a little bit of its history.
Before China came porcelain made by the Chinese (618-906) it was a hard paste made up of Kaolin, a white clay and Petuntse, a feldspar mineral that forms a glassy cement.
It was not commercially produced in Europe until 1710 in Meissen, Germany, although most European porcelain is made of a soft paste using clay and ground glass making it softer than the Chinese.
In England in 1750 bone ash was added to the porcelain giving it the name Bone China, although today the Kaolin comes from Cornwall. It is the bone that gives it its strength and whiteness enabling the clay to be moulded into much finer and more delicate shapes and giving it a translucency that is not possible in porcelain.
Design:A design from conception to production takes on average six weeks to make, with 52 separate hand made processes.
Here is a simplified overview
The initial concept is thought up or commissioned by a client, and after much discussion several designers are set to work to produce a series of sketches, which is then followed by more discussion and sketches and decision's are made
When the client or the company is happy with the design it is then sculpted in Plasticine.
Mould making: There are two types of moulds used, there are the moulds used for casting, pouring the wet clay into and press moulds, for pressing clay into to make leaves and petals, the first type is much more complicated.
The model is carefully cut up into sections, without destroying the surface of the model and plaster moulds are made for each piece, this set is known as block moulds. A mould will only last for about twenty models or it will lose to much detail, so working moulds are also produced.
It takes many moulds to produce one model.
Press moulds, are made by taking an impression of the leaves and petals either from a Plasticine model or sometimes using real leaves, and making a mould to press the clay into.
Casting: Clay is made into slip by adding water, the consistency of the slip determines the thickness of the china, the skill is to have it thin enough to produce a fine piece but thick enough to support itself. Epsom Salts can be added to thicken the slip if necessary
The slip is poured into the moulds, after a few minutes the plaster draws the water out of it, building up a wall of clay on the surface of the mould, making it hollow inside the excess slip is poured out.
As the clay dries it shrinks away from the mould making it easy to release the cast.
The casts are allowed to dry for a while and are then assembled using slip to glue them together and all the seams are taken out and any detail lost is tooled back in.
Flower Making: In order to achieve the delicacy of our flowers and leaves they are all hand made rather than cast.
First the clay is prepared by kneading it rather like bread in a process called wedging
The petals and leaves are made by pressing the the clay into press moulds to get the shape and are arranged in the desired shape and left to dry. When dry they are attached to the model with wet clay.
Biscuit Fire: The model is then propped with supports to stop it collapsing in the kiln and fired at a temperature of 1240 °c. The model will shrink by about 12% in this firing
Gloss Fire: The model is now sprayed with glaze this is infact a thin film of glass and fired again at a temperature of 1050°c. The glaze seals the clay enabling it to be painted.
Decorating Fire 1: The paints come in powdered form and are mixed by the artist using fat oil (dehydrated turpentine) and aniseed oil each artist knowing the consistency of the paint they like to work with. The model goes through the first painting stage or first fire. The paints used are metal oxides and can change colour and intensity due to the temperature of the kiln. The artist knows this and the applies just the right amount of colour, it is then fired at a temperature of 760°c, this melts the glaze and the paint sinks into it. Once fired the colour will never come out or fade,
Decorating Fire 2: The model now has its second coat putting much more detail into the model and is then fired at a temperature of 720°c. As this is a lower fire the the paint actually sits on top of the previous fire giving the translucency that can only be achieved in ceramics
If deemed necessary the model will have third fire to perfect the colour
Gold Fire: If the model requires gilding, 23carat gold is added to the model and is then fired at a temperature of 680°c.
The models are checked at the end of each process and can be rejected at any stage if not up to the required standard.