Home Tips Understanding Stains, Inglazes, Onglazes and Underglazes
| Print |

Understanding Stains, Inglazes, Onglazes and Underglazes.

STAINS

These inorganic colourings are prepared or modified oxides usually available in powder form, for adding to clay bodies, slips, glazes and enamels, as well as, for use in under-glaze and inglaze decorations.

The amount of stain to be used depends upon the desired colour intensity and the ceramic material to be stained.  Full colour is achieved with approximately:

  • 5% of stain in translucent glazes.
  • 10% of stain in opaque glazes.
  • 15% of stain in bodies.

For uniformity of dispersion without a trace of specking it is necessary to mix hot water with the stain and pass through a 200# sieve before adding to the bulk material being stained.

Stain stability is linked with its refractory nature, thus all stains have a temperature limit above which colour changes and or loss may occur. You should check this when considering stain colours and the intended use. Most prepared stains are intended for use in oxidation firing conditions and will often not withstand reduction.

INGLAZES

Inglaze ceramic colours are applied over the top of an unfired glaze, during firing they sink into and become part of the glaze.

Inglazes are pure oxides, prepared stains or glazes that have been strongly coloured.

ONGLAZES

Also known as overglaze colours or onglaze enamels are used to decorate already glazed and fired surfaces and further fired in oxidation at a lower temperature to fuse them to the original glazed surfaces.

Most Onglazes are opaque and are detectably raised from the surface of the initial glaze.

Onglazes are applied by brush, spray gun, litho or engraved transfer, as well as dusting onto a ground medium. Carrying media used for Onglazes are usually oils or varnishes, however, water based preparations can be used.

Onglaze decorations can have poor resistance to abrasion and chemical attack, making them unsuitable for decorating functional ware.

UNDERGLAZES

Are colour concentrates that can be applied to both green and bisque ware which are later fired with a transparent glaze.

Underglazes are suitable for decorating hobby earthenware, earthenware, midfire, stoneware and some porcelain bodies. Colour suppliers specify the temperature limits for their products and care must be taken as some colours will change colour or lose their colour when fired above the recommended temperature range. The colour supplier may also suggest careful selection of glazes as it could also effect colour outcomes. Most underglazes are dull or changed if fired in a reducing atmosphere.

As well as a bright colours range, an added advantage of underglaze decorating is its resistance to abrasion and chemical attack as it is protected by the clear glaze covering.

Underglazes are available in both powder and liquid form. If using the powder form, it is often best to use it with 'painting medium' which assists in increasing the drying time, thus allowing more decorating time.


http://www.clayworksaustralia.com