Suspending grog in a slip

[Sprakeloos]

Dear all

This is my first post here, having been a lurking reader for a while. 

I would like to suspend some coarse particulates in a porcelain slip. I am intrigued by the coarse feldspar inclusions in some Japanese wood fired pottery. I have tried adding coarse inclusions in a porcelain body, which fired well but the large chunks got in the way of my preferred style of handbuilding and surforming the surface. 

I now want to try to add these particulates in a porcelain slip that I can apply to my pots by dipping. 

Does anyone have any tricks on how to suspend larger particulates in a clay slip, eg grog or coarse inclusions? Do grogged slips exist? 

I was thinking that perhaps adding bentonite could help due to its thixotropy, but I am not sure. 

Any help from this very helpful forum in my self-learning endeavors would be much appreciated 

 

Best

Joris

The Netherlands 

 

[Magnolia Mud Research]

I add “chunks” of wild raw clays, crushed bisque shreds, and/or small rocks to porcelain at a consistency of toothpaste.  Application is with a pallete knife or stiff brush.  I mix the paste as I need it using bagged porcelain, water, and “chunks” to get the thickness needed for the project; the leftovers are stored in a closed container as a starter for next project.   Compression of the paste onto the substrate has been the key for success in my work.  Shrinkage cracks are assumed to occur and are considered part of the design. 

[Sprakeloos]

Thank you Magnolia for you very fast reply! This is interesting and I will certainly give it a try. You mention compression of the slip as a succes factor: does this have to do with the bonding of the slip with the body underneath? Does this mean that dip application of a slightly thinner version of this slip with inclusions will not work? 

[Magnolia Mud Research]

23 minutes ago, Sprakeloos said:

You mention compression of the slip as a succes factor: does this have to do with the bonding of the slip with the body underneath? Does this mean that dip application of a slightly thinner version of this slip with inclusions will not work? 

Yes,  I compress the paste into the body with the pallete knife as it is applied.  Brushing usually works ok for the slip, but the 'big chunks' sometimes fall out if the applied layer is too thin.    My 'chunks' range in side from less than half a millimeter to five millimeters;  it is the larger ones that are more likely to have adherence problems if not compressed, especially if the applied layer is thinner than the 'chunk'.    Make small test forms to try out variations of the technique; pay attention to what you do and what actually happens at the wet, drying, and final steps.    When I have used thin slips without big chunks, no problems with pouring or brushing application.  Have not tried dipping.  

[jtf945]

I just found this thread in researching adding grog to slip.  I was told that a 30/80 mesh grog was a good starting point.  Originally I was going to buy some and wedge it into my clay but someone on FB Clay Buddies suggested making a slip and painting it onto my pots but stir constantly to keep the grog suspended.  I have a couple of questions I hope someone can answer.  Should I scratch the pot lightly to insure my slip will stick and since I work with a brown clay body (Highwater Red Rock) does grog come in different colors  or will a light color grog pick up the color of the clay as I do not intend to glaze the outside of the pots.  I am looking for a finish similar to the attached. . . I am looking for a finish like the one pictured . . .

[CactusPots]

That looks a lot like my post "Is that a Glaze?"  I think it's probably different that what Maggie Mud is suggesting because the application is so even.  It's hard to see from this picture if it's grog or sand.  I'm wondering if the variations in color of the individual particles don't suggest sand rather than grog.  I have a few experiments in the kiln I'll be unloading tomorrow, all sand though.

I also think using porcelain slip to suspend the grit will give a much different finish.  This one looks just like mine, real sandpaper finish, no sign of a binding agent.  Yes?

[liambesaw]

That's some larger grog, I think you may be surprised how fine 30/80 is. 30 mesh being the largest size, is half a millimeter.  

You can make any color and size grog by smashing vitrified clay, and then dry sifting (outdoors, upwind, with a respirator) to classify material.  The thicker you mix the slip, the better the particles will be suspended

[oldlady]

JTF,   you mention scratching the surface so i wonder if you have let the pot dry too much for the slip to adhere.   the best time to add slip is just after making it.  before trimming if your final design allows for that.

[jtf945]

9 hours ago, CactusPots said:

That looks a lot like my post "Is that a Glaze?"  I think it's probably different that what Maggie Mud is suggesting because the application is so even.  It's hard to see from this picture if it's grog or sand.  I'm wondering if the variations in color of the individual particles don't suggest sand rather than grog.  I have a few experiments in the kiln I'll be unloading tomorrow, all sand though.

I also think using porcelain slip to suspend the grit will give a much different finish.  This one looks just like mine, real sandpaper finish, no sign of a binding agent.  Yes?

I am not sure if this is a glaze or not.  I want a texture similar to this on my pots and figured the best way to get it is to add grog to slip. I do not intend to glaze the outside of my piece.  Maybe I should try adding sand to my slip and see what results I can get . . .

[jtf945]

9 hours ago, liambesaw said:

That's some larger grog, I think you may be surprised how fine 30/80 is. 30 mesh being the largest size, is half a millimeter.  

You can make any color and size grog by smashing vitrified clay, and then dry sifting (outdoors, upwind, with a respirator) to classify material.  The thicker you mix the slip, the better the particles will be suspended

I only mentioned 30 mesh as I was told that would be a good place to start.  Being new to this idea I would like to get a texture similar to the one pictured so not really sure about which mesh size to purchase . . .

[jtf945]

I read the article from the above shown pot with grog and found that the grog was 20x48 and  found where I could buy it at a resonable price although shipping was almost 3 times the cost of the grog and cheaper to order 5 pounds as opposed  to 1 . . . we'll see how it goes.  On another note I did add a large quantity of builders sand to some slip and applied it to a pot with a pallett knife, it will go into the kiln this week . . .