What you should know about porcelain.

 

Porcelain is a specific type of ceramic material. 

 

The necessary ingredient that differentiates porcelain from other types of ceramic products is a naturally occurring ore, called kaolin.

 

Kaolin is mined in several parts of the world.  It is a pure white powdery substance.  When added to elastic, naturally occurring clays, it allows the clay to be fired in an oven at very high temperatures (1900 to 2300 degrees F).  During this process, the clay melts and turns into a glass-like or stone-like material.

 

Fine porcelain is a white, glassy, and durable material.  A fine piece of porcelain is even-colored and blemish-free.

 

Porcelain is commonly known in two forms: 

• Hard Porcelain

• Bone China

 

Hard Porcelain is a combination of white ball clay, kaolin, and feldspar.

 

Ball clay has decayed organic material in it, such as ground up dead leaves or plant material.  This allows it to stretch so that when the clay is fired, it will not crack.

 

Kaolin allows it to hold together when fired to temperatures necessary to melt it.

 

Feldspar is a very hard rock and gives the ceramic item strength.

 

When hard porcelain is fired, it is non-porous.  That is, the ceramic is solid all the way through.  When water is applied to unglazed hard porcelain, the water will not penetrate it. However, at the high temperatures necessary to melt the clay into a solid, it has a tendency to droop or “slump”.  These shapes tend to slump even more.  Thus it is difficult to make hard porcelain that is thin and shapes that are not warped.  For this reason, the English created bone china.

 

Bone China is composed of the ingredients listed above. In addition, 40% bone ash is added to the unfired clay.  This gives the porcelain shape “bone structure”.

 

Bone ash allows the clay to be produced thinner and slumping does not occur in the oven.  It is possible to make porcelain that is translucent.  However, bone china is porous, is fired at lower temperatures and therefore is more fragile that hard porcelain.

 

What to look for in an excellent piece of porcelain.

Clear and blemish-free surfaces.

 

Porcelain is primarily white, but just like your palette of whites at the paint store; the ore mined at different locations to make porcelain can have slight shade differences.

 

Early Chinese porcelains had a definite gray-blue cast, which we call gray body.  Mottahedeh makes many Chinese reproductions and gray body is often used.

 

The porcelain of Limoges is what we call French body and it is a very bright white with a blue cast.

 

The porcelain of Portugal is a soft white with a warm yellow cast.

 

No matter what the tone of the white you see, just like perfect crystal has no bubbles, perfect porcelain has not spots.  Spotting occurs when a bit of dust or a fleck of metal gets mixed into the clay or glaze. A good porcelain factory is extremely clean and neat, so as not to contaminate the clay.

 

Complex or difficult shape, while remaining thin or light.

 

Getting porcelain to “stand up” in the oven is difficult.  It is like understanding the stress places in the gothic church.  To arrive at a new shape or master an old one, technicians must make a model that may slump, but will slump to an intended appearance when the porcelain is finished being fired.

 

Complex shapes are often made by pouring liquid clay into plaster moulds.  This requires handwork.  Many times it is not possible to make a lot of pieces at any one time.

 

Beautiful color and delicacy of decorations.

 

Once upon a time, that is, for the last 2000 years, porcelain decoration was painted by hand. Nowadays, 98% of porcelain is decorated with lithography or silk-screened decorations.

 

Instead of using ink, porcelain decorations are created using naturally occurring oxides or stone.  It was discovered by the Chinese that permanent pigments could be created by using these elements:

 

 

 

When the oxides are fired onto the porcelain, they turn into stone and are fused to the plate.  The challenge is to get all the oxides to balance chemically and fire at the same temperature, under the same conditions, every time. 

 

The colors on a decoration are printed next to each other and are usually applied to the porcelain all at the same time.  The industry average for colors on a dinner plate are 4 to 10 colors.  At  Mottahedeh, we start at 4 and make decorations with up to 27 colors.  Our average is 16 colors.

 

Is the decoration vibrant, clear, colorful, gentle, bold, subtle, and timeless?

 

These are the things to look for in beautiful porcelain. Whatever it is, it should be “all-the–way”.  The plate or object should represent whatever that quality is with conviction. For this reason, everyone may like something different, but he or she will have a clear reaction to the statement made by the object.  The object will still be appreciated today and also in 100 years.

 

To summarize our understanding of excellent porcelain it must represent these:

• Purity of body.
• Pleasingly light and unusual of shape.
• Brilliance of color and definitive style.

 

If you have not already, we hope you will develop a love for this art form and build a collection of your own.