Ceramic dinnerware (and ceramics in general) is usually divided into three common grades, and then subdivided within each grade.

The common grades of ceramic used for modern dinnerware and tableware are:

• Earthenware
• Stoneware
• Porcelain

Each grade of ceramic is distinguished by the quality and purity of the clay used to form the product and the firing temperature reached in the kiln to harden the product.

The U.S. customs department classifies ceramic tableware based on two tests:

• water absorption
• light translucency

Generally speaking, lower firing temperatures can be equated with less density, less resistance to water permeation, and less resistance to cracking and chipping. Practically speaking, both stoneware and porcelain are so dense and fired at high enough temperature (over 2,100 degrees Fahrenheit) that water permeation is not a problem, and both grades, being high-fired ceramics, are resistant to cracking and chipping.

A fully vitrified body is not porous, it is solid. Accordingly, it expands and contracts at the same rate, unlike a porous body that contains air and moisture. A porous body will weaken much faster than a vitrified body. Professional restaurant dinnerware usually is made with a vitrified body.

Another measure of vitrification for dinnerware is the amount of water in the ceramic body, after it has been fired. Most factories measure a vitrified ceramic as containing less than 1% water in the body. Semi-vitrified ceramic contains 1% to 3% water in the body.

So why is Vitrified so important?

A Vitrified ceramic body is much stronger than a non-vitrified body. It is more chip and crack resistant, and will handle the stresses of temperature change caused by dishwashers, microwaves, ovens, and freezers far better than a non-vitrified body.

]]> http://www.topdinnerware.com/dinnerwareregistryandregistries/what-is-the-meaning-of-vitrified-as-it-applies-to-dinnerware/feed/ 0 http://www.topdinnerware.com/dinnerware-information/what-kinds-of-ceramics-are-used-to-make-dinnerware-or-ceramics-101-part-1/ http://www.topdinnerware.com/dinnerware-information/what-kinds-of-ceramics-are-used-to-make-dinnerware-or-ceramics-101-part-1/#comments Thu, 22 Jan 2009 14:26:32 +0000 admin http://www.topdinnerware.com/?p=21 First, lets start with – What is ceramics?

A basic definition of Ceramic would be:
Ceramic – any of various hard material made by firing a non-metallic mineral, as clay.

Ceramics are dinnerware or objects that are made from baked clay. The production of ceramics involve mixing powdered clay, a tempering medium, and water to create a paste or slip. A paste combination could then be made into a desired form. Slip is more liquid in nature and would be poured into a mold to create the desired shape.

The clay shape is then dried. Surface treatments like decoration or glaze may then be applied. The clay shaped object is then fired, and achieves a level of vitrification, where the particles of the clay fuse together. The high temperature of the firing has the effect of changing the physical properties of the clay object. For example, clay when exposed to water will turn to mud. After firing, the ceramic stays solid when wet.

Ceramics are usually classified in two categories:

• The nature or materials of the paste or slip from which the ceramic is made
• The type or style of surface treatment

The ceramic industry (not the dinnerware industry) separates the materials classification into three categories:

• Earthenware
  • The softest
  • Least vitrified
• Stoneware
• Harder than Earthenware
• More vitrified than Earthenware
• Porcelain
  • The hardest
  • The most vitrified (i.e. most glass-like)

The discussion of surface treatments for ceramics will be covered in a future post.