China clay to ball clay plasticity

[tomhumf]

I've got a recipe I use on bisque ware that has 25% China clay. 

I'm now doing mostly raw glazing with my base raw glaze having 30% ball clay, no China clay. 

I've tried adding the same colourants to my raw glaze recipe but it doesn't look anything like. 

I'm going to try adding some bentonite to the China clay recipe to try and get it to work with my raw glazing method. I'm glazing while they are hard leather hard. 

I'm thinking something like 3 - 5 % bentonite? But maybe someone can estimate better... I know it's quite hard to add bentonite in after mixing a glaze, so want to try get it right first time. 

[Magnolia Mud Research]

My procedure that came from Mel Jacobson: 
It works for me.  
First mix bentonite with water in a separate peanut butter jar to a consistency of thick molasses syrup, but not stiff molasses syrup;  then allow the syrup to "age" for several days. The aging insures that the bentonite and water has equilibrated; if the syrup thickens add more water, mix, and age some more.   

Then add small amounts of the bentonite syrup to the glaze slurry and mix vigorous.  When making a fresh batch of glaze using bentonite, follow the same strategy, mix the batch without bentonite, thoroughly mix the slurry, add bentonite syrup, mix thoroughly.  

When making the bentonite syrup, keep track of how much bentonite you used for the jar of syrup and scale that to how much bentonite is in a spoonful of syrup. then you can measure the bentonite syrup by volume. 

LT
 

[tomhumf]

Ok great thanks, I like the idea of making the slurry. I've started one off today.

I just weighed 5g of bentonite and will use all in a 100g test mix of my current bisque glaze, and go from there depending on results.