flocculants

[yedrow]

I was told that if I use calcium chloride as a deflocculant it would in time turn my kiln into basically the same thing as a salt fired kiln; and ruin it. Granting calcium chloride is a salt, intuitively I would think that sodium and potassium salts would be the cause of such.

 

Is there anyone out there who knows whether or not calcium chloride can have this effect?

[Chris Campbell]

Well, a disclaimer here that I am not a chemist but my gut says the small amount you would use as a deflocculant would take a heck of a long time to equal one salt firing ... It's kind of like using a pinch of salt or a whole cup per firing ... But I could be wrong.

[Mark C.]

I agree with Chris on that. But if you are feeling this way and you are working with slip wares why not switch to Darvon7 as a defocculant

If its just a glaze additive do not sweat it and change to any other kind.

Mark

[bciskepottery]

From Hamer and Hamer, The Potter's Dictionary of Materials and Techniques: "Calcium Chloride . . . A highly soluble and deliquescent crystalline compound. It is used to flocculate clay suspensions. Four teaspoon of concentrated solution of calcium chloride are sufficient to flocculate up to 100 g of bentonite, This expands the bentonite in a box-like jelly structure which holds non-clay minerals and inhibits their sedimentation."

[Radagast97]

I was told that if I use calcium chloride as a deflocculant it would in time turn my kiln into basically the same thing as a salt fired kiln; and ruin it. Granting calcium chloride is a salt, intuitively I would think that sodium and potassium salts would be the cause of such.

 

Is there anyone out there who knows whether or not calcium chloride can have this effect?

 

 

No, it won't. Calcium has relatively low vapor pressure. Also remember the amounts in a glaze a fairly low. If they were higher it would affect the clay and glaze. Once the glaze starts to melt, it really doesn't care what compound the calcium came from - it just sees it as calcium oxide. If you want a substitute for calcium chloride with an extremely low vapor pressure, use a little epsom salts (magnesium sulfate). It does the same thing, flocculation-wise, with zero vaporization potential.

 

Sodium, lithium, and potassium salts have a much higher vapor pressure - which means if a pot is glazed with a high potassium/sodium/lithium glaze and is close to an unglazed pot, you'll get a hint of a vapor glaze on the portion closest. I take advantage of this property by adding a small amount of potassium nitrate to my wax-water emulsion resist. It turns the unglazed feet of my pots from an uninteresting peach color to a light toasty color. YMMV

 

Keep in mind calcium chloride forms very low melting point hydrates and is excellent at sucking water out of the air. Keep it in an open containing on a warm, humid day and you'll return to a big puddle.

 

That said, soluble calcium or magnesium compounds (and on +2 charged ions) with flocculate a glaze, not deflocculate. To deflocculate you use something like sodium silicate. However, most people don't want to deflocculate their glazes. Casting slips are deflocculated, but I've never seen anyone deflocculate a glaze. A deflocculated glaze will settle into a thin, hard, concrete like layer that's hard to mix back up. See: http://www.claytimes...eadjusting.html

 

Rad

[Matt Oz]

Just to be nitpicky, you are actually flocculating when using calcium chloride.

 

I think you mentioned that you read Pete Pinnell's article on adjusting glazes, if you haven't here it is.

 

Adjusting Glazes for Application

 

Lots of good information.

 

update

WHoops, never mind, Rad said it too, it's a good article.

[neilestrick]

I'm a big fan of epsom salts for flocculating glazes. Cheap, and easy to pick up at the grocery store when I run out.

[neilestrick]

Just to be nitpicky, you are actually flocculating when using calcium chloride.

 

 

 

Not at all nitpicky. The terms flocculant and deflocculant have been used to mean the same thing during this thread, which they are not. Flocculants stick particles together, specifically we want our heavy glaze materials to stick to the clay particles in the glaze so they don't settle out in the bucket. Deflocculants cause particles to repel each other. They allow us to make a thinner/runnier slip without adding water, like for casting slips. Be aware of which you are using!

[yedrow]

Thanks for the information Rad. I learned some chemistry. I'm understanding that CaCl and HCl both work in a similar way by generating Cl anions that pick up the Na cations and convert them into low energy salt. Keep in mind this is new knowledge to me and I'm likely to get it wrong. By pulling the Na cations away from the clay the clay ends become polar and create a repulsion/attraction action that causes the 'card stack' phenomenon (Hammer). Your pointing out the low vapor pressure of the metal alkalies answers my question. I was figuring that Ca would be more difficult to 'move' since it is less ionic, per se.

 

CaCl as a floccullaent causes a reversible change, though it isn't easily reversible. HCl's change isn't reversible. I was thinking that MgS yields a reversible process in water too. I may be wrong about that though. From all of this it seems that HCl is the best flocculant. I wish to avoid it though since using it at work corrodes all the tools.

 

Is there a particular reason (Niels provided one) for choosing a particular flocculant?