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Saki

How To Create Thicken Slip For High-Relief Surface Decoration?

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I'm trying to add some decoration to my pots by applying slip. For example, I throw a pot, slather it with slip, and then run my fingers or a rib through it to create texture. The trouble is that once the clay dries and the water in the slip evaporates, the design does not stand out from the surface very much. 

 

Is there a way to create a thicker slip? I am currently using Standard 365 porcelain and I make the slip by adding just enough water to my trimming scraps that I can get a smooth paste by running through a sieve.

 

Thank you.

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Thank you both.

 

John, can you recommend a clay:water:deflocculant ratio? I have some Darvan, but the I read that if you use too much it can have the opposite effect, so I am not sure how much to use to create a workable thick slip. Casting slip seems too thin...

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Just use a very very small amount and see what happens-Since you have not said how much volume of slip you have its harder to tell you how to fix it (details)

That's why I asked for a ratio of clay/water/deflocculant. If you say add 0.01mL for 0.5 pints of water and 1 lb of clay, I can adjust accordingly. I will need to make a new batch, so I can start from whatever ratio you provide. Thanks.

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I' do not have a ratio as I'm a by the seat of your pants guy. I would add a very small amount and go from there.

The other thing you can do is slake down more clay in slip and power mix it -keep adding clay until it what thickness you want.There is a article in current Pottery making illustrated Nov/Dec issue on just this technique.

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Guest JBaymore

There IS no set 'ratio'.  The local water chemistry and the particular recipe of raw materials affects the amount. 

 

Unless you have a syringe or a tiny graduated cylinder, the smallest addition you can easily control is "one drop".  In a really small amount of slip....... 'one drop' can have a profound impact.

 

I'd mix up 2000 grams of the dry recipe and then add just enough water (measured) to make it a REALLY thick mix.....as in way too thick to be "smooth" and creamy like you want it (use a kitchen blender).  Typical specific gravity for water in such slips BEFORE adding the defloculant is between about 1.6 to 2.0 .  For your "thick slip" you want to be heading toward the 2.0 end of life if you can.

 

Then add single drops of the Darvan (is it #7?) and stir it in VERY thoroughly until it suddenly STARTS to get far more fluid.......... just a tad thinner than the consistency you'd like it for application purposes. Stir it REALLY well for a good long time.  (Use a blender/mixer.)   It'll likely go from 'not good' to 'fluid' with that one single critical drop.  Them let is sit for a while.  In this case you WANT it to get a bit stiffer within maybe 1/2 hour. 

 

If it does NOT get thicker.... then cut back the Darvan by one drop on the NEXT test batch... and try again.

 

In this case, you WANT the slip to go on very fluid for application quality.... but to sort of "set up", rather than tend to run off the vertical sides of the pot via the impact of gravity over the initial drying time. 

 

Count the drops you used.  Now you know the water to slip recipe and amount of defloculant needed.

 

Once you know this GENERAL ratio... then you can make it again... and / or make larger batches.

 

best,

 

.........................john

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I've never had much luck with deflocculated slips, they kind of sagged or sort of slid down on the non flat surfaces of a pot. I've had better luck with a slip that is formulated to go on thick and not crack without using a defloc.

edit: works better when I don't overdo the defloc by adding too much and then having to correct it.

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John Britt is the best. I love his Clay Club in Asheville.

It was an honor to have contributed to his Mid-range firing book. He reworked some of my glazes into Oribe green for example. He is such a generous potter.

Marcia

I think I must have posted this in the wrong place. sorry.

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I make a slip for coating a thrown pot by taking a chunk of clay from the bag, chopping it into about half-inch cubes, and then mixing with some water using a hand-held blender. It usually does not take much water.  It is sometimes easier to add the cubes to the water in an upright blender and quit when the slip bogs the motor.  The method comes from a Matt Long workshop years back. 

 

It works for me. 

I have not had any problem with flaking or cracking if I apply to the pot while still on the wheel. 

If the slip is too thin for my liking on any given day, I either leave the lid off for a while or just add a a few 'cubes' of clay and blend. 

 

LT

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Hi Saki, for my thickened slip, I use dried trimmings from my clay. I weigh out 1000 g of the dry trimmings, and to this I add 730 g water. For my purposes, 12 drops of Darvan thins it to where I want it to be. This is a small enough batch size that I can use my immersion blender for the mixing. Yours will be different but perhaps my recipe will give you a starting point. Best wishes, Owen in Bend Oregon where we awoke to snow this morning!

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I've never used slip before, but wanted a small amount to experiment with.  I tried cutting up some thin semi-wet clay (exposed for about an hour on the work table), putting it in a pint jar (Talenti) and filling it with water - expecting to need to let some of it evaporate later, and stirring.  Two days later it hadn't really changed.

I tried Magnolia Mud's upright (kitchen) blender approach in the school's glaze lab.  It worked, but I didn't do my second batch - because:

- It was an awful mess to clean up

- I lost some slip that I couldn't scrape off / out of the blender

- It took some time, as these blenders only stir material up to the top of the blades, so I had to stop, stir and push it down several times

I decided to create a new batch for the second clay, and try a new approach.  I rolled a thin slab, say 1/16" - 1/8" and let it dry for several hours, then cut it into roughly half-inch square pieces.    No doubt drying overnight would be even better.  I put this into a Talenti jar and added hot water to the top of the clay.  Immediately the clay started dissolving, and I decided to pour off some water while the clay content was still quite low.  I gave it a day to process, stirred, and it was ready to go.  I'm sure the large mixers are better for big batches, but the hardest part of this process was dicing the clay after it had dried.  A benefit is that the processing takes place in the same container that it will be stored in, so there is no waste and minimal clean-up .  YMMV

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My first try at the blender, disaster! Since, I add clay a small pinch at a time; the blender (garage sale special) will run up to about a quart and a half of thick slip.

Sieving to remove the sand (and other stuff) is a big plus for me. From there, if too thin, syringing off water after settling helps.

So far, blender slip applied right after trimming (leather hard) survives bisque and glaze firings; me like it.

Re-slaking bone dry bits, that seems like a great idea!

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