practical information casting slips casting powders specifications plastic clays gradient firings | | Walker Ceramics has an extensive range of prepared casting slips.
Preparation involves only the addition of measured amounts of
water and deflocculents.
We strongly recommend that casting slips should be tested for suitability
prior to any bulk use.
All slips are available in 5
litres, 10 litres, and bulk quantities for your own
production.
**Slips may be coloured with the addition of stains suitable for
clay bodies.
Superior White Porcelain (AB10)
A fantastic new Australian made porcelain.
All Australian materials. Superb whiteness and strength. Proven throughout
Australia as a throwing, pressing, casting and hand building body.
Renowned for it's
consistency and
workability.
No.10 Stoneware (AB100)
Fires between 1240-1300°C. Excellent
glaze colour development on this white body. It is suitable for both Middle Fire
and Stoneware glazes.
PB103 (AB103)
The classic throwing and pressing body made directly into
casting slip. A fine white stoneware firing to a white colour at 1300 C.
Beautiful workability and excellent glaze fit at Cone 8 -10. Biscuit at 1000 - 1060 C Glost 1280 - 1300 C.
White Earthenware / Middle Fire (AB300)
The body should be biscuit fired at
1000°C (minimum) and then appropriately glazed and fired from 1060 - 1250°C. This
will cover the full range of our standard Earthenware and Middle Fire glazes.
CB1 (AB400)
This body
has excellent pouring and working properties and high green strength. Fires
white.
Biscuit at 1060°C to 1100°C Orton Cone 04 - 03 .
Glost to 1000°C - 1060°C Orton Cone 06 - 04.
Suits
all Hobby Ceramic Glazes. Especially WHG400 Clear Gloss.
Terra Cotta (AB405)
A beautiful rich red Terra Cotta slip. Suits most Earthenware
and Hobby glazes. Biscuit at 1000°C to 1100°C Cone 06 - 03 . Glost to 1000°C - 1060°C Orton Cone 06 - 04.
Auscraft Ultra White (AB450)
This body has excellent pouring and
working properties and high green strength. Fires to Ultra white .
Biscuit
at 1060 to 1100°C Orton Cone 04 - 03 .
Glost to 1000 - 1060°C Orton Cone 06
- 04.
Suits all Hobby Ceramic Glazes. Especially WHG400 Clear Gloss.
Vitreous China (AB475)
**** NEW ****
This body has been designed for the people
who want Porcelain / Stoneware strength with the brightness of Earthenware
colours at Earthenware temperatures. Biscuit
at 1000 to 1060°C Cone 06 - 04 . Glost to 1150 - 1170°C Orton Cone
1- 3.
Bone China
(AB505) **** NEW
****
Fine quality AUSTRALIAN made Bone China.
Beautiful whiteness and translucency second to none!! Biscuit 1000 C Glost to
1250 C.
Limoges 97975 - 1220 C (AB511)
The classic European porcelain now available in Australia.
Beautiful workability, whiteness, translucency and strength. Available in 5 litres, 10 litres, and bulk quantities for your own
production.
Limoges CM10 - 1300 C (AB530)
The classic European porcelain now available in Australia.
Beautiful workability, whiteness, translucency and strength. Available in 5 litres, 10 litres, and bulk quantities for your own
production.
TECHNICAL DATA
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Oxidised Conditions |
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|
|
Body |
Shrinkage % @ º C |
Water absorb % |
Fired Colour @ °C |
Vitrified Temp °C |
Suggested Temp °C |
|
Superior White Porcelain |
10.2@1300 |
<2.0 |
White |
1220 |
1280-1300 |
|
No. 10 Stoneware◄ |
12.5@1300 |
<0.5 |
Grey White @1300 |
1260 |
1240-1300 |
|
White Earthenware / Middle Fire◄ |
2.8@1060 |
16 |
White @1060 |
1250 |
1060-1250 |
|
|
8.8@1250 |
1 |
Grey White @1250 |
|
|
|
PB103 Fine White Stoneware◄ |
12.8@1300 |
0 |
White @1300 |
1260 |
1240-1300 |
|
Vitreous China◄ |
9@1160 |
16 |
White @1170 |
1170 |
1150-1170 |
|
Bone China◄ |
5@1225 |
15 |
Ultra White @1250 |
1250 |
1225-1250 |
|
Auscraft Ultra White◄ |
3.6@1100 |
12 |
Ultra White @1100 |
- |
1000-1100 |
|
CB1 |
5.2@1060 |
13 |
White @1060 |
- |
1000-1100 |
|
Limoges French White 97975 |
13.0@1220 |
<0.5 |
White |
1230 |
1220-1240 |
|
Limoges Porcelain CM10 |
12.0@1280 |
<0.5 |
White |
1240 |
1220-1280 |
* AVAILABLE IN PLASTIC ◄
AVAILABLE IN POWDER
Deflocculants
The amounts of Sodium Silicate or Dispex N40 added to a casting
slip are very critical and too much or too little may each result in the slip
being too thick. If this happens, take a 1 litre sample of the slip and add one
or two drops of Dispex N40. If the slip becomes thinner after stirring then this
shows that more is required to achieve good fluidity. If the slip becomes
thicker then this shows that too much has been added already. Therefore more
clay and water needs to be mixed into the slip in the same proportion as given
in the casting recipe – no more Sodium Silicate or Dispex N40. The recipe can
depend on the quality of the water supply, which may vary from one location to
another and also may be affected by minor variations in the body’s raw
materials.
Maturing the slip
On standing overnight the slip may thicken up slightly. This
will easily reblend when mixing is resumed, even by hand. We recommend that at
the end of the day's production a thin film of water, approximately 2mm thick, is placed on top of the slip. This will reduce water evaporating from the mix, especially in warmer
weather. Simply mix again the following day.
Litre Weight Checks
The most important part of successfully mixing casting slips
is getting the correct litre weight. For accurate and easy litre weight
measurement contact Walker Ceramics for a Litre Weight Bottle and
chart.
Recycling Scrap
Great care is needed to avoid contamination, particularly from
plaster moulds. Scrap should be kept in sealed containers in a plastic
condition. Dry scrap will promote air inclusion in the slip. Recycle by adding a
maximum of 20% of scrap. More than 20% can effect the quality of the slip. We
recommend adding Barium Carbonate (BaCO3) to the
slip to remove
sulphates, which may cause peeling faults. The amount of Barium Carbonate to add
should be 0.1% (25gm per 25 kg bag) of the total dry weight of clay and scrap.
Faults and Remedies
Everybody who casts suffers from time to time from some form
of casting trouble. Walker Ceramics' experience of the industry, combined with the
extensive work done on casting slips in our laboratory has enabled us to connect
the various faults with measurable properties of the slip.
Of course, other factors besides slip properties can cause casting faults, but usually they can be easily noticed; for example, wet moulds
causing slow casting, careless filling causing 'pinholes' or 'casting-spot',
etc.,
The table shown gives a brief description of each of the
common troubles and the suggested remedies. This only gives the direction in
which to move and it is up to the individual to determine how far they need to
go.
Say you were suffering from flabbiness and you increased the
Dispex addition to correct this then found that you began to get brittle ware
with casting spot, then you would know you had gone too far. The following table
will help you in recognizing and fixing common problems. Thixotropy is the
property of slips becoming thicker when they are at rest i.e. "thixotropy
too high" means that the slip thickens up very quickly!
 | In all our slip recipes we recommend a maximum of Sodium
Silicate - adjustment should only be made to Dispex. |
 |
Before making any adjustments make sure the litre weight
is within the stated limits for the body – Use
Walker Ceramics Litre Weight
Bottle and chart |
|
fault |
description |
cause |
remedy |
|
bad draining |
slip failing to drain from narrow sections or
uneven
surface on slip side of cast piece |
fluidity too low
thixotropy too high |
increase water addition (decrease litre weight) or increase dispex
addition |
|
brittleness |
difficult to fettle or cut – giving jagged edges |
thixotropy too low |
decrease dispex addition |
|
casting-spot
scumming |
discoloured patch appearing on the mould side of the article after
firing
scum on surface of slip |
thixotropy too low |
decrease dispex addition or decrease water addition
increase mixing time |
|
cracking |
small cracks on edges or where handles join the body of the article |
thixotropy too low |
decrease dispex addition |
|
flabbiness |
soft casts difficult to handle without distortion |
thixotropy too high |
increase dispex addition |
|
pin holing |
small holes just beneath the surface on the mould side of the article |
fluidity too low – air in slip |
increase water addition (decrease litre weight) or increase dispex
addition |
|
slow casting |
casting time too long |
fluidity too high or thixotropy too low |
decrease water addition or decrease dispex addition |
|
wreathing |
small uneven ridges on the slip side of the article |
thixotropy too low |
decrease dispex addition |
© Walker Ceramics (Aust) Pty.Ltd 2000
Reproduction for commercial use is prohibited.
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