Enamel and its different supports

Ceramics, porcelain, earthenware and metal enamelling: what are the differences?

Enamel, ceramics, porcelain, earthenware... so many terms that confuse people. Let's try to distinguish the specificities of these decorative enamelled objects.

Enamel is a mixture of different minerals, notably silica, kaolin, feldspar and metal oxides, which make up the colorants. These minerals are fused together to form a glass paste. This material then vitrifies under the action of heat on the chosen support. At Plomeïs, we generally enamel our products on steel, but it is also possible to enamel other materials, which fall into two categories: pottery (terracotta, earthenware, etc.) and metals (steel, stainless steel, etc.). Enamel is applied to a support in a variety of ways: by ladle, dip, brush or spray.

 

Ceramics, earthenware and porcelain are the result of very distinct techniques, each with its own characteristics. The type of support used will then determine the type of final object.

A few details to differentiate them

Ceramics is a term used to designate both the manufacture of terracotta objects and the general name given to these objects. Ceramic is a non-metallic material that predates glass and metal, and there are 4 types: terracotta, stoneware, earthenware and porcelain.

 

Porous body ceramics

Pottery is an object made from common clays . After the clay has been prepared, kneaded and left to dry for two weeks, the pottery is fired and becomes porous. This porosity contains insulating properties, such as the ability to retain fresh liquids, and is also fire-resistant. Pottery can be left in its raw state or coated to give it a smoother, non-porous and hygienic appearance. This is known as "glazed" pottery. These glazes consist of powdered minerals and oxides that melt during firing and vitrify during cooling. Firing takes place at between 800 and 900°C. It is this primer that makes the pottery waterproof.

Earthenware is a ceramic material designed to be decorated. It is a porous, opaque clay paste. A layer of glaze is systematically applied to make the decoration waterproof. Uncoated areas remain porous.

There are two types of earthenware:

• Fine earthenware, whose white body is pre-fired and covered with a lead-based glaze. These are watertight pieces used in tableware, for example.
• Tin-glazed" earthenware: the clay is covered with an opaque tin-based glaze called engobe, which covers the entire base body and gives it a white, shiny appearance.

The glaze is fixed on already-fired earthenware. This is why the earthenware is fired once at a very high temperature, around 1050°C for 8 hours, and then a second time at a lower temperature, around 900°C, to set the glaze.

 

Non-porous body ceramics

Porcelain originated in China between the 7th and 8th centuries. It is sometimes confused with earthenware, since both are white in color. Porcelain is a fine, translucent ceramic that owes its white color to the composition of the clay used, kaolin, and to the absence of the oxides that usually color terracotta. It also contains more silica (a component of glass) than other ceramics, which explains its transparency.

Porcelain is totally vitrified, non-porous and covered with a glaze or transparent enamel that reveals the whiteness of the body. The particles that make up porcelain are fine, enabling it to be fired at a much higher temperature, around 1280°C.

 

Like porcelain, stoneware is a ceramic material whose body is vitrified. The first firing is at around 900°C , then once the glaze has been applied, stoneware is fired at over 1200°C. Unlike earthenware, during the vitrification process, the glaze is not only placed on the surface, but enters the pores of the clay and fills it. This makes stoneware dense, solid and non-porous. Since light colors do not stand up well to very high firing temperatures, stoneware is mainly composed of dark colors. However, new techniques now make it possible to gradually incorporate lighter shades.

 

To go a step further... 

To find out how our plaques and signs are enamelled, discover our craftsmanship.