CREATING THE BASE

The base for this sculpture was going to be fairly traditional in style. Firstly I started off by creating a cottle (the white plastic tube form in the images below). In the centre of this cottle was a metal spindle used for attaching plaster blanks to the lathe, making sure that the base of the spindle was covered in clay. Plaster was poured into the cottle to encapsulate the spindle within the plaster,

Once the plaster had set, the cottle and clay were removed revealing the plaster blank on the spindle (below). This was left to dry out for a couple of days to make turning easier.

 Once on the lathe, the blank could be turned. The three images below show the progression of the base.

 

The plaster base was  left on my radiator to dry out fully, then I had to seal the plaster with shellac which is a type of varnish. (see image below)

 

 The plan was to put foundry letters on the plaster with Rupert's name and rank. The problem that I faced was making sure that the letters were central and evenly spaced. The solution I came up with was to draw a circle the size of the base on my work table with a line through the centre, I placed the base within the circle and was able to use the pencil line as guide for marking the plaster. I used Photoshop to produce the text guide, making sure I had a centre line marked, which I could use to line up with the pen mark on the plaster.

Below: Using the print out as a guide I was able to glue on the plastic foundry letters with P.V.A glue, checking the allignment with a steel ruler.

Making the Mould for the Base Part1

1. The finished pattern for the base, is placed on a clean flat board ready for mould making. I drew a circle around the base as well as the central line to help with the alignment later.









2. I then rolled out a piece of clay to about 3mm thick and cut it to fit within the circle by about 10mm. This clay is used to lift the base off the surface of the board.

3. (from above) Realignment of the base.













4. This gap below the base is to allow a little rubber to penetrate underneath, as this will give me a definite edge to work on in the wax later.

5. Below: The base was wrapped in plastic to protect it from the clay layer. 

6. Clay was rolled out to a thickness of approx 5mm and wrapped around the base, this clay will form the cavity for the moulding rubber to flow through later.

7.Below: An extra ring of clay was added around the circumference and then some wedges, these act as keys to hold the rubber into the plaster jacket. Cups where added to the top and these will form the funnels for pouring the rubber, they look like they are up-side down but this is deliberate to allow the rubber to release from the plaster later.

Making the Base Mould Part 3

Above: Once the plaster has set he whole mould is turned around. In this image you can see where I have added an extra piece of clay up the back of the base. This will make an extra thick bit of rubber for me to cut later. Once again I added straws, and the scrim has been removed revealing the bare plaster. 

Below: Circular locks are cut into the plaster surface which will help to lock the two halves of the the jacket together. Clay slip is added to the bare plaster to prevent the next layers sticking. Straws and a retainer wall are also added. 

Below: The plaster steps mentioned previously are repeated to form this half of the mould jacket.

After drawing a circle around the base of the plaster jacket, I opened it up to clean out the clay from both sides (below), this clay is kept to one side so that I can use it to guess-timate the volume of rubber I will need.

The two halves of the plaster jacket are washed, towel dried,  and put back together. Below you can see the pour holes and airs that I made earlier using clay and straws.

The base pattern was unwrapped and given a slight coating of oil, this will act as a release agent for the rubber. it was then realigned  on the base board.

Above: Here I have included an image of half of the plaster jacket replaced, to show how the clay has left a cavity for the rubber. 

Below: The mould jacket is realigned on the board, clamped down, and clay is used to make pour funnels and to seal all of the seams to prevent rubber leaking out.

Base Mould Part 5 Rubber

Once the rubber had cured for at least 24 hours I removed the clay pour cups from the top of the plaster jacket. The excess rubber was cut back to the plaster level on both sides and it was ready to open.

Carefully prising the plaster halves apart revealed the rubber inside. Both halves of the jacket are removed to reveal the bare rubber. I trimmed off the rubber that had risen up the air holes and the flash of rubber from between the two plaster halves.

 

 

 Below: Excess rubber was trimmed from around the keys and once the rubber was taken of the base pattern I set about removing the letters that had become trapped in the rubber surface. The rubber around the letters was also  trimmed to remove any flashes .

Below: Here you can see the extra rubber that was created on the back to act as a location key, this is also the point that I wanted to split the rubber to allow for easier removal of the wax/plaster/casting material that will be in the mould later. It is important to cut this rubber in a zigzag fashion so that it locates in the right position when placed back in the plaster jacket. 

 

Below: The rubber is placed back into the jacket ready to receive the casting material.

 

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Continue Journey 

 

Base Mould 6 Plaster Cast

 

The first thing I needed to do was take a plaster cast from this rubber mould. This 'first pull' cleans the mould and allows me to see if there are any obvious probelms with my mould or how I lay in the casting material.

 

Above: To make sure I got all of the detail I used an old paint brush to paint plaster into all of the letters, without this there is an increased chance of bubbles being trapped in the detail.

Below: Once the plaster had been painted into the details I chose to fill the mould, normally two or three layers, backed up with scrim is used to save on weight and materials.

Below: This first pull revealed that there is still a chance of bubbles being trapped in the lettering as well as on the bottom edge. The following images show the beauty of using flexible rubber.