Making a head portrait in clay part 2 (oven phase)
All right, so we have made (mold) a head of a friend.
What is next step?
We burn clay to make it be hard and durable, as for daily use as pottery and sculpture.
stoneclay/porslin goes thrue a change in degress around 1000° (normaly 950°) and lower slow burn (Lower burning is wee bit safer to not crack if it might be some water/lairbubbels) for sculpture as a head makit a slow burn (stonecaly) It can take up to 12 houres depending on the size and thikness.Thats makes it mealt and become pysical hard ceramical gods for use or sculpture.
The prosess from soft to hard have to change slow, so the water don´t explode the pottery/sculpture. It have to be compleatley dry before it goes in to the owen. If there still is water in it, it can and probably will explode. Historical the process of the first burning phase came around 1600 sentery they say. Some even does bouth first and scond burn in one burn, but they are experts .. So don´t try that befor you know what you are in to...
When the head is done it have to be dry from water.
It have to dry out carefully, it have to be turned around several times so no part dry out to fast and crack. You can se where the parts dry out it gets lighter in the color, and then there is werry important the head are turned around so the dry process don´t make it to crack, some clay are more tolerated and some are not so keep a eye on it every day.
When the head feels like it got same temperature as the room have its time to burn it the first time.
On slow heat. Its a temperature who rise slow in the oven for this kind of sculpture and its because its pretty thick, and by doing that its also (might) make it not to crack in the oven The head was burned in a temperature of 950° Celsius for the first burning. Abouth a tempeture rase of 100 celsius/houre (We burn this one twice times, one to get dry and one for the color) The head did get in the oven in the morning, then the heat in the oven raise slowly, until it reach top temputure. When it have bean burned it takes several hour's to get down in temperature and you can NOT open the oven before its gets bellow 100 Celsius.
If you open the oven before and maybe moved the sculptures It will crack because it can´t handle the fast deferent between the temperature, it goes to fast and it probabley ends up in dust and peace's, so to be on the safe side, do not open before the oven is bellow 100°. The clay we used is stoneclay, there is many deferent sorts of clay and they can demand deferent temperature so be shore of that the oven can get to the best temperature for that one you gona use. It often say on the package what temperature and kind of clay you use on the package, if you are unchore ask the shop you get it from.
There is also a huge among of ovens to be Abel to burn in so I do not get in to that, more then check what oven you can burn in and what is required for that kind of oven, and what materials its needed for it.
The oven we used is a old one, but a good one. And it got a temperature meter on it so we can se what's happening with the temputure and can put in what temputure we wants and how slow/fast we want it to be.
In this case when we got heads who is pretty thick clay we did put a slow process for it to be shore it will hold.. Slower process makes it safer..
If you are getting in to this make shore to know what your oven requires and read a lot in books before so you know what to do exactly before you do it. Don´t take a chance.. That can ruin the whole production AND your oven and that's is a expensive one to replace.....
And you have to know what temputure the clay you got are recomended to . We used stoneclay on the head and dog.
