[Clayart] Making slip

Michael Wendt mwendt at wendtpottery.com
Thu Aug 15 10:56:41 EDT 2019

Snail is absolutely right about leaving the trim scrap undisturbed.
I make casting slip for things I can't throw on the wheel like rectangular 
butter dishes and heart shaped dishes.
If you want even less shrinkage, I would suggest experimenting with various 
tiny additions of sodium silicate to the slake water.
You can use far less water that way which will lower shrinkage dramatically 
while permitting smooth flow.
Example, I use 32 LBS of trim scrap in 15 LBS of warm water containing 3 
fluid ounces of sodium silicate.
As she described, I sprinkle the trim scrap carefully into the liquids and 
then cover and let sit over night.
Sometimes, I have to poke the top layer of material down into the liquid 
after an hour to be sure it all makes contact.
Be sure to cover it tightly.
By morning, all the material is wetted so stirring produces a thick fluid 
that has the same amount of water as throwing clay.
For casting, I add tiny amounts of diluted sodium silicate over the next few 
days until the flow rate is correct for casting.
For your application, you might start with far less sodium silicate/water 
mix until you find the best recipe for your application.
If this helps, please be sure to share your results with the rest of us?
Michael Wendt
----- Original Message ----- 
From: "Snail Scott" <claywork at flying-snail.com>
To: "Clayart international pottery discussion forum" 
<clayart at lists.clayartworld.com>
Sent: Wednesday, August 14, 2019 12:26 PM
Subject: Re: [Clayart] Making slip

> On Aug 14, 2019, at 12:37 PM, Bob Johnson <impaladrive at gmail.com> wrote:
> When you make slip for slip trailing or similar decorations, what mesh
> sieve do you use?  I make my slip from B-mix trimmings and would like to 
> make it as thick as
> possible but also get it smooth…

I wouldn’t bother to sieve a slip or engobe at all, unless you suspect 
non-clay contaminants in your trimmings. When you mix your slip, start with 
dry ingredients, crushed up small. Add some water to the bottom of your 
container, add the dry materials, then add enough water to cover the dry. 
LET IT SLAKE! Do not start mixing until it has fully slaked (soaked until it’s 
fully wet right through.) The size of your chunks will determine how long 
this takes: if nothing is thicker than 1/4”, a half hour is likely 
sufficient, though it does depend on the clay body. (I make slips from 
B-Mix, too.) If you have thicker chunks, wait longer. Don’t disturb it until 
then, or the portions of the mix that have already slaked will become slip, 
and coat the remaining unslaked parts. This will actually prevent them from 
slaking, resulting in annoying lumps. If allowed to slake properly, you will 
get a very smooth slip even without mechanical mixing or sieving. After 
slaking, pour off excess water, then mix. It should end up at a 
mayonnaise-like consistency. You can always add more water back in if you 
want it thinner.

Snail Scott
claywork at flying-snail.com

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