Tips on preventing thick slip from cracking/separating?

[Morgan]

Aloha and happy new year,

Inspired by some others I have been having a lot of fun playing with colored slip from my same clay body, mainly as a way to recycle and try new things (porcelain), but I have not seemed to crack the code, pardon the pun, on drying it perfectly, especially on tall vase like forms. I have got it down pretty well but not where I want it, which is zero cracks

I put it on thick to get a psychedelic'esque look I am going for where the different colors overlap and that is where they seem to crack, or separate a tad from the overlap is a better way to put it.

I apply it while it is well before leather hard, as that seems to help, and then I put it in a damp box for a few days and just slowly open and close that until it is as good as I can get it. Again, I have got it down pretty good where it is, IMO, it is only really noticeable to me as a "flaw" but I really want to not have it happen at all. Considering I am using the same clay body I would think this is preventable.

The only thing I can think really causing it is each slip color is not exactly the same consistency which is is causing them to dry slightly different.

You can check out some pictures of ones that are fine but one has a minor separation you can see if you close enough (second pic).

https://fluxceramicskauai.com/products/olive-oil-dispenser-drippy-waves

Should I look into slip recipes vs my own clay? Anything I can add to prevent? Keep it in a damp box forever?  

Mahalo

[Callie Beller Diesel]

Hey fellow thick slip user! Those are some lovely bottles.

There’s a few things that might be going on here, but they should be pretty easy to fix. I think the best way to go is to keep using your clay body as a base, as it seems to hold colour well. You just have to get it to shrink at the right rate, which just needs a possible tweak or two.

When you say you‘re using recycled clay, are you making it from your throwing slop, or are you using your whole reclaim with trimmings and failed pieces as well?

If you’re only using your throwing slop, you’re making slip out of the finest particles from your clay, the ones that shrink the most, causing the cracks. You should be using either reclaim that has the throwing slop, trimmings and failed pieces all blended together, or purpose mix your slip from fresh clay. If you go through a lot of it, look into whether or not your clay comes in dry bags to make mixing easier. If not, you can slice the clay thinly and slake it in hot water over a lunch break, and blend it up with a stick blender when you come back.

If particle size isn’t the issue, the next thing to look at is water content. Clay shrinks when the water evaporates, so if there’s less water to evaporate, there’s less wet to dry shrinkage. If you still need the slip to flow to get the look you want, you can look into deflocculating your slip. Adding a drop or two of darvan to a very thick slip will make it flow without adding more water. Be sure to mix very thoroughly: a deflocculated slip will flow most readily after it’s been mixed for several minutes. It will appear to set up if it’s left for a few days between uses as well: mixing will bring it back to a useable consistency. 

If you do wind up using the darvan, be sure not to put any failed pieces into your reclaim if you want to throw with it.

Hope that helps!

[PeterH]

An old John Britt video shows how easily the thickness of a slip can be varied by use of de-flocculants & flocculants.
https://www.youtube.com/watch?v=3an-E0Lk8mQ

Which leaves you free to get the moisture content of the slip right for your application, which I assume is similar to that of your throwing clay.

 

[Morgan]

This is great thank you both so much!!

[HeatherArtLife]

Such a great topic! So, funny enough I am looking FOR advice on varied CRACKLE SLIP! Woohoo. So, anyone here like to chime in over there with opposite advice for the kind of surfaces I´m loving...?? @Callie Beller Diesel perhaps? Pretty please. Cheers! - Heather

 

[Callie Beller Diesel]

My suggestion is to do the opposite of what I said to get it to not crack. So you want the piece and the slip to be at different stages of drying/different water content, and you want the slip to shrink more than the piece.

The fine crack pattern you’re looking at means that the slip suggests to me that the slip was applied very thinly, but does shrink quite a bit compared to what it’s applied to.