Thursday, 1 September 2011

How it's made.....casting

I've decided that I might as well make a virtue of necessity and give you an inside look at how our microdolls are made.

The process is long and takes several weeks but it starts off with casting.  I'm currently casting tiny ballerina dolls and new marionettes, but a complete casting batch, completed over several weeks, will also contain toy porcelain animals, marotte heads, Punch & Judy puppets, nursery rhyme and fairy tale characters.... all the toys we create in porcelain.

All of our tiny porcelain dolls start out as a puddle of slip.  Porcelain slip for miniature dollmaking is specially formulated and available in a range of flesh tones as well as white and other colours, which we use for different toys.

It needs have just the right texture and the consistency of single cream.  It has to be stirred and sieved to remove any lumps before casting, whilst taking care not to introduce air bubbles which can leave tiny pin holes on the surface of faces and bodies.

Before I start, I prepare the work area, spreading newspaper to soak up any spills.  Because tiny doll moulds 'set up' so quickly, it is only possible to cast a few at a time.  From pouring the slip to releasing the mould takes around 10-15 minutes, depending on the air temperature, humidity, how dry the moulds are etc, so if I try to do too many at once, I will run out of time to get them all open in time.  For this reason I usually cast up to 5 at a time.

First, I always check inside each mould and remove any dust or dried porcelain slip with a soft brush.  The inside of the moulds are easily damaged and any marks will transfer to the casting.  The mould below is for one of our most popular toy dolls and it's possible to see the head/torso, arms and legs outlined in the plaster.

Once checked, the moulds are tightly re-banded to avoid any seepage of the liquid slip between the seams.

The pour holes are tiny, so the only way to ensure that the porcelain slip gets all the the way inside the mould without drying out halfway down, is to use a syringe.  I insert the tip of the syringe inside the mould and carefully fill each cavity

Just before I begin filling the first mould, I set a timer for the amount of time I judge will be required for the casting to set up.  This varies according to several factors and is where 20 years of experience comes into its own!  When all the moulds are poured they are left undisturbed until the timer goes off.  During this time, water is absorbed from the slip by the porous plaster and the slip changes from liquid to solid becoming leather-hard greenware.

Now I have to move quickly.  If I leave the greenware in the moulds for even a few minutes too long they will dry out and crumble when they're handled.  The castings must be just dry enough to easily release from the mould, but not too dry that they're unworkable.

Again, years of experience will tell me whether the mould will release and open easily.  Trying to open the mould too early will result in the casting ripping apart.  Perfect greenware will release smoothly with every piece intact.

Once open, I gently remove the castings, one at a time, starting with the smallest, most delicate pieces first, usually the arms. Using a scalpel blade, I trim off the excess formed by the pour holes, and make stringing holes with another of my favourite tools.  As soon as the greenware leaves the damp mould, both the air and the heat of my hands accelerate the drying process so I have to work quickly, while still handling the soft, malleable pieces very carefully.  If the greenware is compressed, distorted or otherwise damaged at this stage it will be ruined.  Porcelain has a 'memory' and will revert to its damaged state even when attempts are made to restore the original shape. 

 If I have misjudged the time, or there is any delay in opening the mould, this is the point at which the tops of tiny arms will break off, or cracks appear in bodies so this part of the proceedings is always a little tense.  If the phone or doorbell rings I can't abandon my task, which is why I always give an all-points warning to everyone in the house that I'm doing a casting session and can't be disturbed UNDER ANY CIRCUMSTANCES, short of a life and death situation.

Today's session involved making stringing holes in the limbs and the bodies but other dolls might require the excision of tiny eye sockets, provision for articulated heads or other modifications to the basic structure.  The prepared pieces are then placed on a board to air dry thoroughly.  

Each small batch of casting, comprising 5 dolls, takes at least 45 minutes to complete, from pouring to setting on the board to dry. Needless to say, it takes quite a lot of such tiny pieces to fill all three shelves of my kiln, so the casting process will be repeated two or three times a day, over several weeks, before the greenware can progress to the next stage...... soft firing.


rosanna said...

I cannot wait to read the next episode.

Cate and David said...

Fascinating! And mind-boggling! Thank you for sharing this!

Sandra Morris said...

Thanks ladies. It will probably be several weeks before I can progress to the next exciting instalment.

Thrilling isn't it?


Anonymous said...

Do you drain the slip from the moulds?

Obscure Creations said...

I'm casting with plaster of paris. I wonder if your technique when dealing with flash would work for me. I find unless you do the flash work right after demolding, it gets really hard to shave or carve and kicks up a lot of dust.

anyways - i'm enjoying your blog
From Tyla @