White Midfire Slip Recipe
July 2009
|
|
Recipe |
|
|
minimum |
maximum |
|
Powdered Clay |
25 kilos |
25 kilos |
|
Water Lt |
10 |
11 |
|
N42 Sodium Silicate |
80 gm
60
mL
|
80
gm
60
mL |
Dispex N40 |
15
gm
10.5
mL
|
30
gm
21
mL
|
|
litres of slip produced |
19 to 20 |
|
aim litre weight/grams per litre |
1725 |
|
biscuit |
1060-1100°C Orton Cone 04 to 03 |
|
glost |
1000-1060°C Orton Cone 06 to 04 |
Recommended Method
1. Add water to mixer
2. Add minimum Sodium Silicate N42 diluted 50/50 with warm
water.
3. Mix and put aside minimum Dispex N40 diluted 50/50 with warm
water.
4. Agitate mixer as you add some of the clay. The slip will
gradually thicken.
Add a small amount of Dispex N40 mixture to maintain fluidity. Then add more clay.
Continue this process until all the clay is in the mixer and a
smooth creamy consistency is obtained.
The maximum amount of Dispex N40 should not have been needed to
this stage.
5. Check the litre weight.
If litre weight is higher than the aim, add water.
If litre weight is lower than the aim, add clay.
For accurate litre weight measurement ,contact Walker Ceramics
for a Litre Weight Bottle and calculation chart (Product Code HC80).
6. Mix for 1 hour (more for multi bag mixes) then check if
more Dispex N40 mixture is required for pouring fluidity.
7. Allow slip to mature for 24 hours.
8. Reblend.
9. Sieve through an 80 mesh screen before use.
For multi bag mixes proceed as above but leave addition of
Dispex N40 until final adjustment.
In all our slip recipes we recommend that the maximum amount of Sodium Silicate
is not exceeded.
Before making any adjustments make sure the litre weight is within the stated
limits for the body.
Faults & Remedies
|
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 (slip thickens too quickly) |
increase water addition (if litre weight is too high) or increase dispex
addition |
|
brittleness |
difficult to fettle or cut – giving jagged edges |
thixotropy too low (slip too fluid) |
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 (slip too fluid) |
decrease dispex addition or decrease water addition |
|
cracking |
small cracks on edges or where handles join the body of the article |
thixotropy too low (slip too fluid) |
decrease dispex addition |
|
flabbiness |
soft casts difficult to handle without distortion |
thixotropy too high (slip thickens too quidkly) |
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 (if litre weight is too high) or increase dispex
addition |
|
slow casting |
casting time too long |
fluidity too high or thixotropy too low (slip too fluid) |
decrease water addition or decrease dispex addition |
|
wreathing |
small uneven ridges on the slip side of the article |
thixotropy too low (slip too fluid) |
decrease dispex addition |
Casting
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