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Nelly

Deflocculating--the point of no return?

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Dear All,

 

A few weeks ago I watched a great You Tube by John Britt where he showed how to use epson salts or magnesium sulphate as a deflocculating agent. I was excited. He said that it was how Steve Hill makes his wonderful fluffy slip that he uses to adorn his vessels.

 

While I have done a similar technique using just regular slip and whipping it up, I thought this time I would take some cream consistency scraps and gently add some epson salts. What I noticed and what John Britt said clearly was that you have to use very little of the water and epson salt mixture. I did notice it started to thicken but not enough to my liking. Thus, I kept adding the epson salt and water mixture to the slip.

 

What happened was it turned out very watery. Know that I had already added mason stain to my starting slip base. I did not want to throw it out.

 

Thus, I painted my pots with it anyway as a type of under glaze color.

 

What I noticed afterwards in cleaning up some burrs left by the slip was that using the red rib, it started to shine. Then with a small burnishing stone, I noticed the same thing. It did it much more easily than my other pots that I have applied regular slip and stain. Again, my clay body is a simple stone ware Tuckers body. There is no significant grog in this formulation.

 

Here are my questions:

 

1. Did I create a type of terra sigillata for stone ware?

 

2. Did I make a mixture that will now not hold glaze in the same way that terra sig. won't once fired??

 

My guess:

 

1. I did create something like a terra sig. I think this process is reversible with the sodium silicate but I am not sure and really wasn't thinking about it at the time. It was only while I was driving along in boredom today when it donned on me.

 

2. The pots with this mixture will likely not hold glaze readily.

 

What do you think?

 

Nelly

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Well first of all magnesium sulfate is a floculant not a depfoculant, so if you are trying to defloculate your slip then you should probably use sodium silicate or darvan 7.

 

 

 

Darrel

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Well first of all magnesium sulfate is a floculant not a depfoculant, so if you are trying to defloculate your slip then you should probably use sodium silicate or darvan 7.

 

 

 

Darrel

 

 

 

Dear Darrel,

 

Thank you so much for your response.

 

Your response suggests I am using incorrect terminology. What I am trying to say is that I was trying to thicken some slip with epson salts. I was not trying to water it down. It just happened at some critical chemical and catalytic point. I hope this is a little clearer now.

 

Sorry if there was some confusion with my language.

 

I just really want to know if my glaze will stick with this concoction I made and applied. Again, my apology for the incorrect use of terminology.

 

Nelly

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Nelly,

 

Ive had the best results with this technique using a porcelain slip, more specifically from a porcelain body that uses soda feldspar such as Helios. Using that epsom salt mixture reconstitutes the soda back into the deflocculated slip so it holds up nicely when applied and gives that full bodied fluffy look that Steven Hill gets.

As for your slip, i don't think you made something that wont hold a glaze. I have never had a problem with that solution effecting my glazes negatively so im pretty sure you wont have any problems.

Hope I was able to give some useful info, good luck :)

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Nelly,

 

Ive had the best results with this technique using a porcelain slip, more specifically from a porcelain body that uses soda feldspar such as Helios. Using that epsom salt mixture reconstitutes the soda back into the deflocculated slip so it holds up nicely when applied and gives that full bodied fluffy look that Steven Hill gets.

As for your slip, i don't think you made something that wont hold a glaze. I have never had a problem with that solution effecting my glazes negatively so im pretty sure you wont have any problems.

Hope I was able to give some useful info, good luck smile.gif

 

 

Dear Stephen,

 

Now I remember....he does use porcelain. I have seen a Stephen Hill video and I do recall his clay was porcelain. It is all coming back.

 

That makes sense. I am not sure of the chemistry or words to use, I just know my intent was to get nice fluffy peaks in my slip and it didn't work. Pretty interesting process though. Just one drop too many and you ruin a batch. It is magic.

 

Thus, when I refer to slip that I mix in the blender this is simply called "deflocculated." When I add the epsom salts or mag. sulphate or even sodium silicate or Darvon it becomes flocculated. From my understanding in trying to ascertain the definitions it all has to do with ionic attraction in the solution.

 

I am sure there is some chemistry person out there who understands this much better but my bottom line worry was will the glaze stick when I fire it. I will go with your answer and let everyone know in a week or two when I am finished this load.

 

Thank you for your answer.

 

Nelly

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Sodium Silicate and Darvan are deflocculants. They will make a slip more fluid (watery) without adding water. Generally speaking, it causes particles to repel each other. A little too much and you can make the mix go completely watery. Way too much and it will go very thick and sludgy, like when chocolate seizes up. It is commonly used in casting slips, to make them fluid enough to pour in and out of a mold while keep the water content low so they set up quickly and shrink less.

 

Epsom salt/magnesium sulphate is a flocculant. It acts as a thickener. It is typically used to keep glazes in suspension.

 

Most fluffy slips I have seen are deflocculated. It allows you to apply a very thick layer of slip without it cracking and falling off as it dries. It will stick to any type of clay, stoneware or porcelain. Hope this helps.

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Sodium Silicate and Darvan are deflocculants. They will make a slip more fluid (watery) without adding water. Generally speaking, it causes particles to repel each other. A little too much and you can make the mix go completely watery. Way too much and it will go very thick and sludgy, like when chocolate seizes up. It is commonly used in casting slips, to make them fluid enough to pour in and out of a mold while keep the water content low so they set up quickly and shrink less.

 

Epsom salt/magnesium sulphate is a flocculant. It acts as a thickener. It is typically used to keep glazes in suspension.

 

Most fluffy slips I have seen are deflocculated. It allows you to apply a very thick layer of slip without it cracking and falling off as it dries. It will stick to any type of clay, stoneware or porcelain. Hope this helps.

 

 

Dear Neil,

 

I appreciate your response.

 

Let's see if I have got it...???

 

1. Fluffy slips are deflocculated in that they repel particles by the use of Darvon or Sodium Silicate. This can be done using stoneware but is more done using porcelain. Too much and you make the solution watery. If you use too much you can make a thick hard batch of slip that is useless (i.e., as you said, similar to when chocolate seizes in pot).

 

2. Epsom salts is important for glaze suspension primary and is considered a flocculant. Thus, now that I have this nice big bag of epsom salts I will use it likely to only suspend glaze (and I have a hydrometer) or stick to using it for baths and/or making my grass green. In short, I will stick to the Darvon and SS. I have both of these products as well.

 

Thank you for taking the time to explain this to me. I hope I have it. I think it is rather complex. Perhaps when I start to use some porcelain, I will see the wonders of making this fluffy slip.

 

Nancy

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I think that the main reason people use it with porcelain or white bodies is because they want the slip to match the body, and making a smooth white slip to match a white clay body is very easy. Making a smooth slip to match a stoneware is a little more difficult, but still very doable. The easiest way to do it is to make a slip from your clay body, then screen out the large particles with an 80 mesh sieve. To make the slip without getting all scientific, let a bunch of trimmings dry out to bone dry. Then crush them up a bit into a container and add water till the clay is just covered. The next day, pour off the excess water. You'll have the makings of a thick slip. Mix it well, then start adding the deflocculant just a couple drops as a time. Once it's fluid enough to do so, mix it with a stick blender. Keep adding deflocculant a drop at a time until you get the fluffy consistency you want. Bingo.

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I think that the main reason people use it with porcelain or white bodies is because they want the slip to match the body, and making a smooth white slip to match a white clay body is very easy. Making a smooth slip to match a stoneware is a little more difficult, but still very doable. The easiest way to do it is to make a slip from your clay body, then screen out the large particles with an 80 mesh sieve. To make the slip without getting all scientific, let a bunch of trimmings dry out to bone dry. Then crush them up a bit into a container and add water till the clay is just covered. The next day, pour off the excess water. You'll have the makings of a thick slip. Mix it well, then start adding the deflocculant just a couple drops as a time. Once it's fluid enough to do so, mix it with a stick blender. Keep adding deflocculant a drop at a time until you get the fluffy consistency you want. Bingo.

 

 

Dear Neil,

 

 

Got it. A drop at a time of darvon or sodium silicate. I think the last time I did this was with Robin Hopper's slip that was made from a variety of dry ingredients. I did do this batch with the trimmings but added mason stains and water. Thus, it started out somewhat liquid. I will remember to take he water off after letting it sit for a while. I used a regular blender for the whole lot but maybe should dry the hand hill stick blender. Thank you Neil. I will do this next time.

 

Nancy

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