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Overview of Ceramic Methods from Start to Finish
Molds are made out of plaster. To make a ceramic item, one pours liquid mud, otherwise known as slip into the mold. Plaster has an affinity for water, so it absorbs water out of the slip leaving a thin layer of clay taking the shape of the mold. Slip is kept in the mold for anywhere between five and thirty minutes, depending on the size of the mold. It is then poured out and the mold is allowed to drain. In anywhere between 30 minutes and a full day, the slip remains in the mold until it hardens up enough to be able to stand on its own when taken out of the mold. This is called the leather hard stage.
Once the item is taken out of the mold, it is called greenware. Attachments like separate arms or legs are attached (slipped on -using slip as glue) at this time. Also cut-outs, such as windows in buildings or stars in lampshades are made. Any other similar adjustments to the greenware are made at this time. The greenware is then allowed to dry further until most of the water has evaporated out of the piece. It is important to note that greenware is extremely fragile from the time it comes out of the mold until after it fires in a kiln. Remember that it is only air-hardened mud.
Preparation for Firing
To prepare the piece for firing, it is cleaned. Cleaning involves using a small knife-like tool to remove the seam lines where the two parts of the mold came together making a line on the greenware. It is important to remove all traces of this seam line or it will remain visible for the life of the piece. Further cleaning can be accomplished by a scrubber file. More details can be added with various tools to add back fur to an animal along the seam line or to put initials in the greenware to identify the person preparing it. Fine tuning of the original cuttings or attachments can also be done at this time, making the piece as perfect as possible before firing.
The greenware, after it has been cleaned, is put into a kiln and the temperature brought up to around 2000oF. It takes about 3 hours to get to this temperature. Once the kiln shuts off after reaching this temperature, the piece is allowed to cool for about 17 hours in the kiln. This slow cool down keeps the piece from cracking which would happen if it were taken out sooner.
When the piece as come out of the kiln, it is now called Bisque. The piece is now less fragile and can be handled without so much worry of it breaking. It will still break if you drop it, but it won't disintegrate in your hands if you clutch it too hard as would the greenware. The bisque can now be either painted with acrylics or glazed, depending on the end product characteristics desired.
Bisque may be painted with acryllics, and if done right, will look more realistic if drybrushed. Drybrushing and wetbrushing are techniques that are best learned in a ceramics class. Wetbrushing is applying a brush loaded with paint to the ceramic piece. Drybrushing is a technique where the painter wants the details of the molded item to stand out, such as fur on a wolf. First, the piece is wetbrushed one color such as black or walnut. Then the color of the fur or other detail is added by putting some paint on the brush and wiping off most of it on an old towel. The paint is then brushed across the grain of the piece, leaving the black in the crevices and the color of the fur standing out. Other colors are applied also across the grain, blending highlights, such as white or yellow, with the original fur color. After the piece is done, it is sprayed with either a matte or gloss sealer to protect the paint from rubbing off. The piece is not fired again (It would burn off all the paint applied.)
There are other textures that can be added to a piece that is painted, such as glitter or rough textures that look like rock.
A piece may be glazed in order to make it water tight and give it a glossy appearance. Glaze is, in actuality, glass. If a piece is to have separately colored places on it such as designs or writing, these separate colors can be applied either in the greenware or bisque stage.
In the greenware stage one uses a special clay-based paint called underglaze. When the piece is then fired to bisque, the clay-based paint also hardens to bisque. A clear glaze is then put over the bisque and the piece is fired again.
In the bisque stage, to apply multiple colors, one uses an underglaze for bisque. Depending on the type of underglaze, another coat of clear glaze may/may not be applied. The piece is then fired again.
If only one color of glaze is desired, one would brush on this color of glaze. Various effects can be achieved such a peacock look by using crystal glazes. A piece can be made to look old by using a crackle glaze.
Glazing should also be learned in a ceramics class. The correct amount to apply and how to apply it are techniques that need to be learned.
Gold and Mother of Pearl
Gold and Mother of Pearl are called overglazes. These are applied over a finished glazed piece. The gold application is genuine 24K gold. Mother of Pearl is a mixture of chemicals that make give the appearance of albalone or mother of pearl. Both of these overglazes have to be applied on top of glaze and fired in a kiln at about 1000oF.
If one wants to apply either of these to a piece that is only partially glazed and otherwise to be painted, the bisque must be glazed in the spots where the overglaze will be applied, fired, then the overglaze applied on top of the glaze, fired again, and then the piece may be painted.
© 2003 Indiana Ceramic Supply, Inc.
This page last updated on 10/26/2004