Making and using a former

Here, we make a former for a tumbler, but you can alter the former profile to whatever you want to make. Essentially, you start with a block of clay that’s roughly the right shape, on a banding wheel/whirler, or for large pieces, you can use the head of your wheel, if you have one. A piece of stiff cardboard, or thin MDF/hardboard, is cut to shape to fit over the edge of the wheel (providing stability and consistency) and allow the shaped profile to touch the edge of the clay. By turning the wheel, the former will scrape the clay away to shape it to the desired profile.

 

To make a domed shape (for a hump mould, for example) remember to take the profiled edge of the former right across the radius of the circle, to the centre.

 

You will need:

• Small round wooden batt
• Paper, pencil, cutting mat (optional)
• Sharp craft knife
• Compass, tape measure
• Very thick card or thin MDF, hardboard, etc, for making the former template
• Clay for making the model [from this point on, the materials are to make a complete mould for slipcasting a tumbler/keep cup. If you only want to learn how to make a former, you won’t need these]  and cottle (old clay – reserved for plaster work)
• Mould maker’s size (soft soap)
• Potter’s plaster, scales, measuring jug, bucket for mixing, newspaper, bowl
• Silicone drinking lid. Available widely online

Before you begin:

It’s worth pointing out that the biggest part of this project is the preparation, and this is very important to make an accurately shaped mould, so take the time to complete this part carefully.

 

 1

Make a paper circle by drawing around your wooden batt – this will create the exact size required.

Cut the template out with a sharp knife.

 

 2

 

Fold the paper circle in half twice, to divide it into quarters but, more importantly, to establish the exact centre point.

Place the template over the batt and position the compass point at the centre. Press the point through the paper into the wood. Check that you can see the mark at the centre of the batt.

 

 3

Measure the diameter of the drinking lid – they should be a standard size, but just make sure.

Make a note of the measurement somewhere – the template is as good a place as any!

 

4

 

Now make the template for the cup itself. Decide what height you want it to be, remembering to allow for shrinkage in firing. The chosen height here is 13cm, which seems very tall but the cup will be made from porcelain which has a high shrinkage rate – up to 12%, therefore allowance must be made for this. Decide in advance what clay you intend to work with and scale your measurements up according to its individual shrinkage rate.

So, for example, the silicone lid is 9cm diameter and given that the cup will be made from porcelain the measurement at the top must be scaled up to 10.8 if you intend to really high-fire the clay. However, if you aren’t planning to fire it above 1220°C you can reduce the measurement slightly because the shrinkage won’t be so high – maybe only 10%.

Of course stoneware and earthenware clays will be different, but your supplier should be able to provide shrinkage rates at set temperatures for you to make your own calculations.

Fold a piece of paper in half and draw along the crease with a pencil.

Measure the width you want for the base, along from the central line – here it will 3cm smaller overall than the top, which will be made to 10cm diameter to accommodate the intended firing temperature. Mark a point 3.5cm either side of the central line (10cm­ minus 3cm = 7cm = 2 x 3.5cm).

 

5

 

Measure the 13cm height mark from the base and cut away the excess paper above this line.

 

6

 

Measure and mark out the top of the cup as you did for the base (5cm either side of the central line).

 

 

7

Draw a line from the base to the top, to make a template for the cup.

Fold the template in half along the central line, then cut along one of the drawn side lines.

 

8

 

Open out the template, and make a note of the measurements on it for future reference.

 

9

 

Set the compass to half the size of the top measurement of your cup – 5cm here. Measure it accurately using a tape or ruler.

Set the point of the compass in the pre-made mark on your batt, then draw a circle in thick pencil line.

 

10

 

Measure the distance from the central drawn circle to the edge of the batt and make a note of it.

 

11

 

Assuming your card or board is square, with a perfect right-angled corner, set a ruler against the bottom edge and draw in a thick pencil line as shown.

 

12

 

Fold the template in half and line it up with the edge of the board. Align the top of the cup (the wider measurement) with the line you have drawn at the bottom of the board.

 

13

 

Draw around the template using a ruler to ensure the lines are straight.

Extend the top line (bottom of cup) to the same width as the base line.

 

14

 

Working along the bottom line – from the base edge of the cup outline – mark the distance you measured earlier (from the edge of the circle to the edge of the batt).

From this point, draw in a vertical line down to the edge of the board.

 

15

 

Draw in a final line, a ruler’s width from the last little line but this time connecting the top line to the edge of the board.

The template is the area lightly marked by diagonal lines.

Cut out the template carefully with a knife or saw.

 

16

 

 

When it’s cut out, the template should sit on the batt, extending from the central drawn line and down over the edge.

If all your measurements are accurate, the former will now make a perfectly shaped cup.

 

Here’s an example of a former for a dome

 

Forming the model

17

 

Roughly form a block of clay into the shape of the cup and sit it on the batt, within the drawn circle.

Fill in the gaps around the base with small amounts of soft clay until the shape comes neatly up to the line.

 

18

Sit the former on the batt in the correct position to assess where you need to add clay to build up the shape. Work around the model in this way, correcting the shape where required. It’s better to add too much clay than to have indentations and gaps.

 

19

 

Continue to add clay in small amounts to correct the shape and height, using the former continuously to re-assess.

 

20

 

When the cup is the correct size but still in rough form, turn the batt on a whirler, drawing the former around the edge of the model in a fluid movement to refine the outline of the shape.

You will find you still need to add small amounts of clay to build up the shape but the former will also remove a lot of clay in the process. This is a time-consuming exercise, but getting it right will pay dividends later.

 

21

 

When the model is finished, the former should fit up to the model perfectly all the way around.

Now level the top (or what will be the bottom) of the model with a rib.

 

22

 

Smooth over the surface of the model with a metal rib to completely refine the surface.

 

23

 

Bevel the edge of the base very slightly with a rib.

 

24

 

Place another batt over the model and check that the level is correct with a spirit level. Make any small adjustments required to correct the level if not quite right.

 

25

 

Soft-soap the board around the model (Note: this is not strictly necessary but always best to do if in doubt that the plaster might adhere to the surface)

Wipe back the soft soap with a damp sponge, then repeat the process twice more.

 

26

 

Fit a clay or lino cottle, 4cm from the model.

Whatever material you are using to make the cottle, make sure the ends seal together really well.

 

27

 

Seal around the base of the cottle with a thick coil of soft clay.

 

28

 

If unsure if the cottle will hold, secure it by running some paper tape around it several times – top and bottom. It is perfectly possible to do this on clay as well as lino.

 

Preparing the plaster

Clear away any clay or other materials that could be contaminated by plaster.

Assess the amount of water required to fill your mould and measure it out into a bucket, working on the ratio of 2pt water to 3lb of plaster.

Weigh out the required amount of plaster.

Line a bowl with newspaper and have it nearby.

 

29

 

Add the plaster to the water and mix it up with your hand (WARNING – wear a rubber glove to do this if you have any allergies).

Skim off any bubbles that form, with your hand, and deposit them in the paper-lined bowl.

 

30

 

When the plaster begins to thicken, pour it over the model, allowing at least 4-5cm excess above the top of the model.

Shiver the surface of the plaster with your hand to raise any remaining air bubbles in the mixture, then allow the plaster to set.

As it sets, a chemical reaction is triggered and the plaster will heat up. It’s ready to continue working on when this process has finished and it’s cooling down again.

 

31

 

Remove the paper tape reinforcements from around the cottle and then the cottle itself.

 

32

 

Surform the edge of the mould to a rounded shape, to remove all sharp areas that could break off and contaminate other materials.

 

33

 

Turn the mould over and surform the upper edge to an equally rounded shape.

Deposit all the shavings in the paper-lined bowl used earlier. Try to keep the plaster contained as much as possible to avoid contamination – being a neat worker really pays off when working with plaster!

 

34

 

Very carefully, spoon out the model from the mould using a wooden tool, taking care to ensure the tool doesn’t come into contact with the plaster wall because it will easily mark at this stage.

 

35

 

Wipe out the interior of the mould with a damp cloth to remove all traces of clay.

Place the mould somewhere warm to dry out thoroughly before use – it will take some time – at least two weeks.

 

 

 

 

 

 

 

 

 

 

 

 

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