Question:
How do I fire porcelain?
Underglazes and one-strokes
It is possible to decorate porcelain bisque with underglazes and one-strokes. This has to be done at a soft bisque(018) since porcelain fired to maturity would not absorb the colour. Some of these colours change when high-fired so it is best to run tests on colours
vitreousity
During the firing process, porcelain becomes vitreous or water tight so there is no need to glaze the inside of pieces. Although glaze should always be used on utilitarian ware.
Draping
Cotton lace is the only kind of lace that will work effectively for porcelain draping. In the technique of porcelain lace draping, a piece of cotton lace is saturated with porcelain slip and added to a doll. When the piece is fired the cotton lace burns out leaving a fine shell of porcelain athat was in the originally saturated lace.
Shrinkage
Did you know that porcelain will shrink approximately 15% during the firing process.
Glaze compatibility
Some clear glazes are not compatible with porcelain and will not take the high temperature. Be sure you check to see if you are using the proper type.
Most clear glaze for porcelain is fired to cone 2 or 3.
Precautions
If you do not fire porcelain properly, the various colours that porcelain is available in will not be true.
When firing porcelain, your kiln must be very clean. To ensure that it is, you should vacuum it out before a porcelain firing.
Finishing
When you remove porcelain pieces from a bisque firing, you will note that they have a slightly rough feeling. Before decorating, polish them with a 100 grit scrubber until you have a soft satin finish.
Cleaning seams
Because porcelain shrinks, it is necessary to do a good job of cleaning the seams off since a ridge will form when fired.
antique porcelain
You may antique porcelain soft bisque (018) much as you would any other ceramic piece.
Colours
Because porcelain comes in a variety of colours, it is not necessary to paint a background on porcelain pieces.
Dry-foot porcelain
All porcelain pieces must be dry-footed since they cannot be supported by stilts during a glaze firing. If you should attempt to do so , the stilts would go right through the bottom of the piece.
Retard cast setup time
Plasticizer may be added to porcelain slip to retard the set-up time.
It is possible to use porcelain to double cast as well as create the wedgewood porcelain technique.
Lustres/decals
Lustres or decals may be fired onto a unglazed piece of porcelain bisque.
Some decals when fired directly on porcelain bisque will change colours so they should be test-fired before ruining your favourite piece.
Temperature.
A kiln capable of reaching a temperature of 2250 degrees (cone 6) is necessary to fire porcelain.
Description
One-strokes are concentrated colour pigments with no clay added and may be translucent or opaque.
Soluable in water, one-strokes can be used for washes, outlines and small areas of concentrated colour.
One-strokes are not recommended for large area coverage. These are concentrated colours and will streak if not applied properly.
As the name implies, only one coat of colour is needed when using one-strokes.
Setters
Some pieces having overhangs must be fired on a setter or they will sag or collapse during firing.
Setters are not used during the glaze firing of porcelain.
Preventing sagging
You can help prevent porcelain cups from going out of shape during the firing by kiln washing the rims and placing one cup on top of the other, rims together and handles opposite for balance.
Handling greenware
If you are a little afraid of handling delicate porcelain greenware, you can fire it to 018 before cleaning.
Position in kiln
Porcelain pieces should be kept at least two inches from the side walls or elements of your kiln during firing.
Application
One-strokes may be used on either bisque or greenware.
As the name implies, only one coat is necessary.
Stilting
Porcelain pieces cannot be stilted when fired, and pieces cannot touch each other since the high temperature will make them stick together. Your kiln shelves must have an adequate covering of kiln wash as well to keep them from sticking.
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| Jolyn Wells-Moran |
