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Casting Slips

Casting Powders    Casting Slips    Casting Slip Recipes     Casting slip records

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.

Imperial Porcelain 4317 (AB1)
An amazing, white, translucent world class Australian made porcelain.  Superb whiteness and strength. Fully ball milled for the smoothest of results. Fires from 1220-1300°C. Suits all standard stoneware glazes.

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.

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.

Terra Cotta  - add Terra Cotta Concentrate to your choice of white slips.

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.

White Midfire (AB175)  
This body has been designed with extra whiteness for the people who want Porcelain / Stoneware strength with the brightness of Earthenware colours at MIDFIRE temperatures.
Biscuit at 1000 to 1060°C  Orton Cone 06 - 04 .
Glost to 1200 - 1220°C Orton Cone 5-6.
Suits our range of Mid Fire glazes.

Bone China (AB505)      
Fine quality AUSTRALIAN made Bone China. Beautiful whiteness and translucency second to none!! Biscuit 1000 C Glost to 1250 C. Use EN250 Clear Glaze

TECHNICAL DATA

Oxidised Conditions

Body

Shrinkage % @ º C

Water absorb %

Fired Colour @ °C

Vitrified Temp °C

Suggested Temp °C

Imperial Porcelain 4317 *

13.2@1300 0 sNOW wHITE 1220 1220-1300

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 ◄ *

2.8@1060

16

White @1060

1250

1060-1250

8.8@1250

1

Grey White @1250

White Midfire ◄ *

9.9@1200

<2.0

White @1200

1200

1200-1220

Bone China

5@1225

15

Ultra White @1250

1250

1225-1250

Auscraft Ultra White◄ *

3.6@1100

12

Ultra White @1100

-

1000-1100

* 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 Walker Ceramics 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

Casting Powders    Casting Slips    Casting Slip Recipes     Casting slip records

 

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Copyright © 2010 David Walker / Ozclay Pty. Ltd. All rights reserved.
Revised: December 22, 2010 .