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Bisque or low fire glaze firings (04-06) usually require 5-7 hrs firing time. Porcelain and stoneware high firings take from 6-10 hrs.
|To completely dry the ware for glaze firing?|
|To make the ware easier to store?|
|To prevent thermal shock in the glaze firing?|
|To harden the work in order to glaze it?|
To glaze our pots, we will usually be dipping them in liquid glaze. If we dip greenware in liquid, we run a good chance of it absorbing too much water and falling apart. This is why we bisque fire the work before glazing. The main purpose of the bisque firing is to harden the work in order to glaze it. Bisqued clay (or bisqueware) is porous, so it will absorb water to ensure a sufficient glaze coating. Bisque firing also burns off organic compounds in the clay (molds, bacteria, lignite, carbonates, and sulfates) that can cause problems if they burn off through the glaze. For stoneware firing the bisque is usually fired to about cone 06 (18400F).
|Not brightly coloured glazes?|
Do not place greenware and glazed ware in the same load. The gasses emitted by greenware may cause discolouration of the glaze. If it is necessary to mix glaze and greenware pieces when firing a load, the glazed pieces should be packed in the lower part of the kiln with the greenware above.
|The reaction of the glaze over a dirty piece?|
|An explosion of the body due to improper glaze fit?|
|An explosion of steam due to incorrect drying of the glaze?|
|A slow rise in Kiln temperature?|
Crawling 26882 Glaze will creep/crawl in the firing if the bisque was oily or greasy, dirty or dusty. You can salvage the piece by re-glazing and re-firing.
|The ware will explode?|
|The glaze will crawl?|
|The ware will shrink more than is usual?|
|Your ware wil have a cloudy appearance and often an impaired finish?|
Kiln ventilation If you do not vent your kiln properly when firing, your process will have a cloudy appearance and often an impaired finish.
|Incorrect glaze application?|
Poor colour in coloured glazes can be caused by over-firing. This is especially true of red glazes which are usually fired at a lower temperature.
|Trim/turn ware on a chuck?|
|Fire ware slowly?|
|Compress the base?|
|Add more grog to your clay?|
S cracks To prevent cracking in the base of thrown pots (s cracks): center and compress your clay once, then cut from wheelhead, turn upside down and center again. This way the base becomes highly compressed, preventing cracking. A proven technique
|The type of glaze used with a body?|
|The positioning of glazed ware in the kiln?|
|The glaze and body expand and shrink a like amount when heated and cooled?|
|The thickness of the glaze in comparison to the body?|
- Glaze and body fit Glaze and body fit? Since the glaze and the body on which it is fired (bisque) are made from different materials, it is important that they expand and shrink a like amount when heated and cooled. If they don´t, then the fired glaze can be stretched to the point where it can crack (crazing), or it can be pushed together on to itself to a point where shivering or crawling occurs.
|Adding combustibles to the firing?|
|Reducing the temperature at different stages during the firing?|
|Firing down in the cooling?|
|Robbing the clay body and glazes of part of their oxygen, thus changing their colour and texture?|
Reduction Firing A reduction firing is an incomplete burning where smoke and soot (the excess carbon) rob the clay body and glazes of part of their oxygen, thus changing their colour and texture.
|A plastic that burns out during firing?|
|Refractory material used to prevent kiln furniture/ware from fusing ?|
|A material used on throwing bats, to enable the ware to be moved easily?|
|A coloured slip like paste, used for textured decoration?|
What is Bat wash? Bat wash is a slurry of refractory material used to prevent kiln furniture from fusing together or pots fusing to shelves or to their lids when fired in position. The ideal wash is one which is relatively cheap and should be easy to make up into a wash which stays put during setting, and lastly it should easily wash off the foot rims, lids etc of the finished ware. A mixture of aluminium hydrate two parts, china clay one part will be found excellent for most purposes both oxidized and reduced.
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