White Slip Newbie

[missflo]

Hi all,

I just joined your lovely community. And I was wondering if someone could advise me on making my first white slip. I've been trowing some stoneware pots and I would like to decorate the inside with white slip.

I have a pack of 25kg of this deflocculated porcelain dust clay in my studio:  http://www.vdiez.com/catalogo/porcelana-sa-2.html?lang=en  and when I asked advice to salesman I was told I could just add water and apply it directly on the stoneware. Is this true? I know that porcelain has a different shrinking percentage that stoneware, therefore I'm a bit confused. Can anyone advise me with this?

That would be amazing. Thank you

[oldlady]

welcome to the forums.   it would help to know where in the world you are, i am guessing not the USA by the use of kg in your post.  

it is true that adding water to the powder will make slip.  it is also true that it might not work with your clay.   it is also true that you might test the slip and clay to see if it does work.    sometimes there is no apparent problem in the beginning but a badly fitting slip will peel off over time.   i bought one fantastic lidded canister that has a fabulous matte glaze and a great shape.  unfortunately, the slip around the rim has peeled up and flaked off.   i still admire it but it lives on a high shelf and is only a visual treat.

there are technical folks here who will be able to help you but would like to know lots more about the clay you use.   do you have any info that will help them?

[Magnolia Mud Research]

I  use porcelain clay to make "white slip" for various  stoneware. I take wet porcelain from the bag, add water to get the consistency (aka 'thickness') of the slip, and either brush it on or apply with a palette knife.  After the sheen disappears, I compress the applied slip into the stoneware.  The compression is important to prevent voids that leads to cracks and delamination of the slip.  
I work at cone 10 reduction.  Have used white slips made from cone 10 porcelains, and from cone 5 porcelains and have not had problems other than delamination as mentioned. 

Try it on some pieces, and develop an application technique that works for you.  

LT
 

(I have also done the reverse, using stoneware slips on porcelain to produce "texture and color" in the surface.  ) 

[liambesaw]

A lot of the catch-all slips are fluxed to help them stay on whatever clay they're going on after they're fired, I guess that would be one difference between mixing your own and using straight porcelain.  But porcelain is fairly well fluxed to begin with so may just work as is.

[Callie Beller Diesel]

If you already have this porcelain slip, it’s free to test it. The shrinkage rates don’t have to be identical in my experience. This is one example where it’s ok to be close enough. 

The description of this slip says it’s already deflocculated, so that will help prevent the slip cracking off as the piece dries, which is more of an issue if you wish to apply it thickly. If you wish to make a dipping slip suitable for leather hard work, this is ideal as the slip will flow better, and there will be less water in the slip that could soften a partially dry piece too much. The deflocculant means you won’t have to add a lot of water, so go easy and mix thoroughly. Because of the deflocculant, I would not let any slipped pieces get into your reclaim.

Welcome to the forum, and let us know how it turns out!

[missflo]

Wonderful thank you everyone! I will give it a go

Ideally I should apply the slip at a leather hard stage right? 

I have a few bone dry pots that I thought to paint white inside, but maybe it is a good idea to try with some fresh ones instead?

 

[Callie Beller Diesel]

Leather hard is best, yes. If you try applying slip to bone dry, you’ll slake the pieces down because this is the point where clay absorbs water most readily. 

[missflo]

Thanks