iandol on sun 25 aug 02

Dear Waltraud Koestler,=20

I am making an assumption but it sounds as though your failing to =
achieve the height you intend from you pound and a half of Porcelain =
Clay.

My first thoughts are that you are using pure water as a lubricantand =
that you have a very soft clay.

Because of the open nature of plastic porcelain clay it tends to adsorb =
fresh water very quickly. The first point is that this reduces its =
strength. The second is that water is a poor lubricant so you are not =
reducing the stress of throwing by reducing the "Torque" or twisting =
motion of the wheel as it pulls the clay around past your fingers.

My first suggestion is that you use the slip which develops during =
throwing as a lubricant. This give two advantages. First, as water is =
sucked into your clay it drags in very fine clay particles which help to =
seal the surface against further water adsorption. The second is that it =
is a slippery material so it gives better lubrication and reduces the =
drag as you pinch into the clay.

I suggest you change your technique once you have centred and opened the =
ball of clay. Pull the upper third or half upwards first, then then next =
portion below, then the lowest portion. this splits each pull up into =
three parts so it may seem to take longer, but it does not. What it =
gives is mechanically strong clay below the point at which you apply =
pressure. This is better able to resist the twisting motion of the wheel =
and the slowing effect of your fingers.

Timakia@AOL.COM on sun 25 aug 02

It depends on how long it takes for you to get to that point. Porcelain clay
is very thirsty. For that reason you will have to get the hight that you want
in almost 3 pulls. It will also help if you can start out with your clay a
little drier than normal and then use as little water as possible.(a clay
slurry will even be better) Till you are experienced enough it will also help
to pull a little and let it sit for a while to dry a little bit and then
carry on(if you have the time). Hope this will help.

Antoinette Badenhorst
http://hometown.aol.com/timakia
105 Westwood circle
Saltillo, MS
38866

Jon Faber on sun 25 aug 02

Waltraud,
To state what may be blatantely obvious, sounds like
the bottom is fatiguing.

This could be for a bunch of reasons.
1. Porcelain likes loads of water.
The top may be drying out causing extra torque on the
bottome.

2. Metal ribs are really useful for porcelain.
Because of the purity, porcelain sucks up the water
and spreads out thus fatigues easier.
The metal rib is the best for compressing the clay
letting you get thinner.

Also, you may need to leave some extra clay at the
bottom until the last pull.

hope that helps
jon



--- Waltraud Koestler wrote:

---

>

Hello,



I've some problems to throw cylinders using
porcelain.

Up to now I've thrown very small pieces with
porcelain.



I tried to throw cylinders using about one and a half
pound of clay.  

If I pull up the clay it starts warping in the lower
part.

It starts already during the second or third pull.



When I cut the clay through to check the thickness of
the wall, it's

nearly perfect even.



What's the reason of this problem?



Could someone help me?





Waltraud



from Germany

align=left>
http://www.planet-b.net - Das
Internetportal für Bertelsmann-Mitarbeiter und Ihre
Familien.

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