Porcelain is generally divided into two types: hard-paste porcelain and soft-paste porcelain. As the name suggests, the two differ in their degree of hardness. How this difference arises and what other properties hard-paste porcelain have, you will find out below.
Manufacture of hard-paste porcelain
Hard-paste porcelain consists of around 50% koalin (china clay), around 25% quartz sand and around 25% feldspar. The high proportion of china clay is responsible, among other things, for its high strength. The raw materials are mixed and ground.
- Also read - What is soft-paste porcelain?
- Also read - The properties of porcelain
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Then metals and impurities are filtered out with the help of a magnetic tape and a sieve.
The mass is then shaped into the desired shape using one of three possible techniques.
Now this form has to pre-dry in the air.
Then the porcelain is fired for the first time at around 1000 degrees.
After this first firing, the porcelain is already very hard and can no longer be worked with conventional tools. The shape can only be changed with diamond and sandpaper. It has now lost all water and the mass has shrunk by 3%.
Now the still glowing porcelain is glazed. The glaze of hard-paste porcelain is also significantly more resistant than that of soft-paste porcelain.
The porcelain is then fired again, this time at significantly higher temperatures of up to 1500 degrees. Here the porcelain again loses about 20% of its mass.
Properties of hard paste porcelain
Both the shards and the glaze of hard-paste porcelain are particularly hard due to the high content of koalin and the hot firing temperatures. The hardness during firing is due to the fact that crystalline, granular and powdery substances combine. Hard-paste porcelain is less fragile because of its hardness. However, since objects made of porcelain are usually very finely crafted, the porcelain will likely break if dropped due to its delicacy.
Due to the high firing temperature, the color palette of hard-paste porcelain is limited, so that objects made of hard-paste porcelain are often white or pink.
Difference to soft-paste porcelain
Soft-paste porcelain has a significantly lower proportion of koalin and the second firing takes place at significantly lower temperatures. You can find out what else distinguishes soft porcelain here. Bone porcelain is a special type of soft porcelain. This porcelain also has a lower proportion of koalin and also contains a high proportion of burned cattle bones.Tips & Tricks If you have dropped your favorite hard-paste porcelain cup, you can glue it yourself in just a few steps and with just a few tools. You can find out exactly how this works here.