Bone china cups are just a wonderful way to enlighten the atmosphere of your dining room and show your friends and family your love for elegant high-priced china wear. Bone china cups are different from ceramic products due to two aspects; bone ash content and two times firing in the bone china cups manufacturing process.
The durability, whiteness, appearance, translucency, and strength of bone china cups make it really unique from any other variety. Have you ever wondered how these beautifully decorated cups that we use every day are manufactured?
The bone china cups manufacturing process consists of complex machinery, skilled technicians and workers.
The manufacturing consists of 6 main steps:
●Clay making.
●Mould making and forming.
●Biscuit firing.
●Glazing.
●Glost firing.
●Decoration.
Let us understand the manufacturing process in a bit more detail so that you can appreciate your bone china cups a little more!
Essential Raw Materials
The raw materials used in bone china cups manufacturing process are:
●Bone ash.
●Kaolin.
●Lime.
●Feldspar.
●Clay.
●Flint.
●Silica.
Bone ash consists of about 40-45% of bone china products and is the main element which enhances translucency.
Bone ash is also the major contributor for the white appearance of the bone china cups that is otherwise not available in other porcelain products.
1. Clay making
●Mixing the raw material
In the first step of clay making, the raw materials are mixed with a certain quantity of water and then the mixture is blended at a high speed in the ball grinding mill machine to form the slurry. The grinding time is proportional to the size of the particles and it usually takes a day.
●Sieving
This step includes sieving the slurry in order to eliminate the iron and other impurities.
●Formation of slip
The next step consists of reducing the moisture level from the final mix to about 20% by pumping it into a filter press. The final mixture left after this step is known as slip.
2. Mold making and forming
In the next step of bone china cups manufacturing process, the clay is diluted and cast into molds. These molds are the foundation of all the shapes- mug, bowl, plate, etc. It requires high skills and expertise.
In order to make the product, these shapes have to be molded. This step is called Forming. The forming methods differ according to the shapes. For forming the regular round products like bowls and plates jiggers are employed, whereas the irregular pieces like gravy boats and pots are cast in plaster-molds. Square, rectangular and oval pieces require a stable shape. Thus they are cast inside two-parted plaster molds. The formed bodies are called green wares and are left over to dry.
3. Biscuit firing
Biscuit firing is carried at temperature ranges of about 1200-1300 centigrade in which the green wares are fired over 15 hours in the oxidizing atmosphere in the biscuit kiln.
So as to achieve the best results, the firing-schedule must be carefully controlled. The prime aim of this step is to vaporize volatile contaminants and reduce shrinkage during the firing.
Polishing and selecting
After the first firing, biscuit wares are formed which are then sent for a bath. Smooth stones and water are used in order to polish each biscuit ware so that the rough exterior can be removed. After this, each biscuit ware is passed to a giant industrial-dishwasher and dryer.
4. Glazing
Apart from bone ash, the other thing which makes the bone china cups stronger than other porcelain products is the glaze. You can consider it as a liquid glass that once heated can form a very strong protective shell.
Glaze consists of bone ash and Kaolin. Since the biscuit is nonabsorbent, the gaze is applied by spraying. The irregular biscuit wares are glazed with a hand which requires a steady hand and patience. In order to ensure that the foot of every piece doesn't stick to the kiln, it is cleaned with a damp sponge.
5. Glost firing
Glost firing also called as the second firing’ is the next step in the bone china cups making process. After the glaze dries, the pieces are fired for a second time at 1080 degree Celsius for over 7 hours in the glazing firing kiln. If you wish to avoid direct contact with the flames, the glazed coated biscuits are sent in the saggers. When the temperature reaches 1000-1200 centigrade, the glaze will melt and fuse onto the biscuits.
All the biscuits that come from the kiln after this step are cooled and carefully inspected for any imperfections. Only few can make to this level and are then passed for the final stage which is decorating.
6. Decorating
Bone china cups come in a variety of designs that ranges from flowers, geometric designs, animals to even holiday motifs.
The standard decorating methods of Bone China cups include:
●Spraying
●Decal application
●Gold finishing
●Hand painting
You can now apply the decals with hand or machines. In this process, any dust is removed first as it can interfere with the effect of the decal. You can place the decals by hand on the plate after soaking them in water.
Gilding refers to the application of precious metal like Gold or Platinum on the white ware. The metal is manually applied on every piece with the help of a delicate brush. As for other pieces that need edging in a wide metal rim, machines are employed. Hand painting and gold or platinum decoration are applied by skilled, well-trained artisans.
It does not matter the application, the decoration needs to be fired for one last time at 700-800 centigrade so that the pigments can fuse in the glaze coating. With decal and gold rim decoration, the pieces need to be fired for two more times. Different temperatures are required here.
The decoration step ends the Bone china cups manufacturing process. The qualified pieces are inspected strictly for one last time and sent for packing.
Final Thoughts
Now you might have realized that those shiny beautiful cups whose quality and appearance mesmerize you are not that easy to manufacture. It requires deep prowess, experience, hard work and time. It is only due to this complex and detailed bone china cups manufacturing process that the final products are worth buying. Besides, you could know how to choose the bone china cups manufacturer for yourself.