Flocculating and deflocculating

[Cyndy Littleton]

I am a fairly new potter with a question regarding glazes that separate so badly, it is a constant battle to keep them in suspension. I recently mixed the blue green/ red copper glaze listed on the Ceramic Daily site. It does not stay in suspension long, has to be constantly mixed prior to dipping, and goes on unevenly. I read an article about flocculating glazes and different techniques to help with suspension. But my question is "How do you know how much to add to the glaze?" The article recommended using epsom salts, but did not indicate how much or how do you know when it is too much. Any suggestions?

[Brenda B Hardt]

I just added so much water to Orange Red (got from Stephen Hill with 12.1% bone Ash) that it no longer has the spots and burns out a bit.  Then I learned that I could have added Darvan 811 (or other -- let me get my mind around this!)

In case this helps another beginner:  here's a recap of what I just picked up from John Britt's video.-- Thanks for posting!

A glaze can "go basic" or Deflocculate.

So you want to flocculate it by Adding an acid such as Epson Salts or Calcium Chloride (first dissolved in water) you can see the glaze puff up and get thicker. 

If the problem is that the glaze has "gone acid" or Flocculated and looks very thick

and upon application, shrinks and cracks and flakes off the pot, then you will want to ADD Darvan 7 or Darvan 811 or Sodium Silicate (do a small test batch of this addition to test if this will be a remedy for your whole bucket before adding to the whole bucket)

Restating this (hoping I got it right) will be helpful to me in the future when I have forgotten what John Britt  said on the video.

My question is:  what are the signs your glaze needs to be flocculated? (hard pan at bottom?) and how do you know that your glaze didn't just dry out and needs water and really doesn't need to be deflocculated?

If this info is elsewhere, I would just appreciate a link; and forgive me for not doing my homework.

[Norm Stuart]

I think it's easiest to focus on Calcium Ca+2 and Magnesium Mg+2 ions, which flocculate and suspend glazes by attracting the negatively charged clay particles into a floc around the positive ions. This helps keeps the negatively charged clay particles apart and repelling each other.

For a peaceful life please do not look any further into this explanation as it concerns "field strengths", "molecular geometry" and the interactions these molecules and ions have with water. I just tell people calcium and magnesium ions suspend glaze - magically. It works, so that's explanation enough for me.

Calcium and Magnesium are also the ions which make water "hard" leaving those white sediments on plumbing.  I simply sprinkle in Calcium Chloride crystals which attract water and give off heat as they dissolve quickly. Too much Magnesium (epsom salts) has a greater tendency to make glazes crawl, plus epsom salts don't dissolve as easily. Calcium and magnesium also make glaze hard after being fired.

Deflocculants, like Darvan or Sodium Silicate, "suck" the Calcium and Magnesium out of the glaze water - by ion-exchange, replacing each Ca+2 and Mg+2 (calcium and magnesium ions) in the glaze water with two apparently useless sodium Na+1  ions, just like a water softener does.

Sodium Silicate actually forms a little bit of insoluble calcium silicate (wollastonite) or magnesium silicate (talc), adding only the extra silica and sodium to the glaze.

The Darvan attaches the calcium and magnesium to its polymer chains where the sodium was formerly attached. All but the sodium burns out as an organic.

With the calcium and magnesium gone the glaze to deflocculates and settles.  This is why "soft water" makes glazes hardpan - all of the suspending Ca+2 and Mg+2 were "removed" by the water softener. The added sodium can be easily removed by pouring off the excess water from the settled glaze. But only adding Calcium and Magnesium ions can suspend the glaze again.  

As you suggest we could also flocculate the glaze with the H+ hydrogen ions provided by an acid.  This creates several problems at our studio.

1.) Acids like Vinegar or Hydrochloric react with the carbonate found in many glazes creating foaming as carbon dioxide is released as the acid is neutralized, leaving no flocculating free H+ ions;

2.) The discussion of H+ ions can create the false impression that the state of flocculation or deflocculation is fundamentally about glaze pH, rather than ionic attraction and repulsion. Most flocculating ions have no effect on the glaze pH.

3.) This third flocculating ion H+ leads to a discussion of a fourth flocculating ion like Al+3 ions which can be added as Aluminum Sulfate (alum), and the list keeps going.

Worst of all - Any a reasonable person following this explanation would ask, "why is a positive ion flocculating not offset by the deflocculating effect of the negative ions?

EDIT:

Daniel Spruyt, a Cone6Pots member who's a proper chemist, has been helpful in clarifying that:

a Flocculant is an ionic molecule with a strong anion (+ charge) and a weak cation (- charge).

The concept that how much the field charge of a positive or negative ion charge is felt in solution, varies (by where the missing or added electrons are) is a concept I vaguely recall from my college chemistry courses.

It explains why the negatively charges cations (like chloride or sulfate) which should tend to deflocculate are quite weak in strength so are overwhelmed by the flocculation produced by more powerful anions (like calcium, magnesium or ammonium), leading to a strongly net flocculation effect.

So Thanks to Daniel Spruyt for explaining this!

Salts like sodium Na+ and potassium K+ ions added as an raw material (soda ash & pearl ash), or over time by leeching out of feldspars and other raw materials through bacterial action, make glazes hard-pan.  Rehydrating and adding calcium chloride will have no effect on a hard panned glaze without the additional use of a chisel or spatula with a lot of muscle to help intersperse the the newly added hard water ions (calcium and magnesium) work their way between the clay molecules and re-suspend the glaze. Better to add too much calcium chloride initially.  We buy ours on Amazon.com sold as a sidewalk de-icer (it gives off heat as it absorbs water).

How much?  An amazing 745 grams of calcium chloride dissolves in a liter 1,000 grams of water - less if the weight of the calcium chloride included water it has already absorbed from the air, which it does quickly. That makes really hard water. I just sprinkle in a few grams of calcium chloride and to stir to see if that's enough. There's no test paper or meter you can use to determine this in advance.

As a bonus, Darvans of a slightly different design are primarily used by water agencies who add it to drinking water and to waste water. The Darvan polymer attaches itself attract bacteria, virus, and silt into a goo they call a "Floc" which is a completely different definition for the word flocculate, "gathering together" - which is then filtered out by a bed of sand.

Brenda B Hardt said:

I just added so much water to Orange Red (got from Stephen Hill with 12.1% bone Ash) that it no longer has the spots and burns out a bit.  Then I learned that I could have added Darvan 811 (or other -- let me get my mind around this!)

In case this helps another beginner:  here's a recap of what I just picked up from John Britt's video.-- Thanks for posting!

A glaze can "go basic" or Deflocculate.

So you want to flocculate it by Adding an acid such as Epson Salts or Calcium Chloride (first dissolved in water) you can see the glaze puff up and get thicker. 

If the problem is that the glaze has "gone acid" or Flocculated and looks very thick

and upon application, shrinks and cracks and flakes off the pot, then you will want to ADD Darvan 7 or Darvan 811 or Sodium Silicate (do a small test batch of this addition to test if this will be a remedy for your whole bucket before adding to the whole bucket)

Restating this (hoping I got it right) will be helpful to me in the future when I have forgotten what John Britt  said on the video.

My question is:  what are the signs your glaze needs to be flocculated? (hard pan at bottom?) and how do you know that your glaze didn't just dry out and needs water and really doesn't need to be deflocculated?

If this info is elsewhere, I would just appreciate a link; and forgive me for not doing my homework.

[Brenda B Hardt]

Norm- Thank you so much for this important info about flocculazation which I will set aside time to really understand and digest.

 I appreciate the warning about the WaterColor Green not liking your  slow cool schedule so guess I can plan to keep Warm Jade and Clear Blue and other glazes in a separate firing than my Stephen Hill glazes.

I wish I new my Skutt kiln well enough to know what to do.  Based on what u told me, here's what I will try as I have several pieces with Warm Jade and several with Clear Blue(with Minspar) in this load.  Wish me luck.

200/hr to 240F

100/hr to 500

450/hr to 2100

100/hr to 2170  (SH range 2160 to 2190)

cool to 1800, 50F/hr  HOLD 30 min

to 1700, 50F/hr Hold 30 min

to 1600, 50F/hr hold 30 min

to 1500,  50F/hr, no hold. Kiln off.

That would be a 8 hour COOL DOWN period. hmm?  you said 6 hour was your schedule.  I'll hold off firing until I hear from you again, if you are willing.

[Norm Stuart]

I've read most Cone 6 glazes supposedly start to "set-up" at 1,800 F, and are nearly frozen at 1,500 F. I suspect this varies from one glaze to another. But we cool at 50 F per hour between 1,800 F and 1,500 F without any holds except at the peak cone 6 temperature for 20 minutes to allow reacting glazes time to lay down.

What I do know from experience is glazes which are partially crystallized during our slow-cool, such as Zinc Silicate glazes become even more crystallized if added to a bisque firing to 1,888 F.  Although the bisque firing is not slow-cooled, it simply provides additional time in the crystallization zone, both on the way up and on the way down in temperature.

But most glazes fired in our slow-cool do not show no additional changes when refired in a bisque.  So an even slower slow-cool with not change their appearance.

Since it's my understanding that most glazes are still liquid at 1,800 F, I don't understand why the 50 F per hour slow-cool in the schedule you're using begins at 2,170 F, nor the 30 minute hold once you get there. But I wouldn't be surprised if there are some glazes which do start to set up hotter. 

The additional 30 minute holds at 1,700 1,600 and 1,500 F would all create more complete crystallization than our slow-cool does - as witnessed by the changes we see after a second firing in a bisque load. These holds and slow-cool at a higher temperature will increase firing costs.

Our slow cool is faster than yours, but slower than the 185 F per hour suggested by Ron Roy and Jim Hesselberth in "Mastering Cone 6 Glazes"

This is an example of Ron Roy's Sapphire glaze, fast cooled, slow-cooled at 185 F, and again at 50 F.

You can see, more time in a slow-cool provides more crystallization with this glaze. Not a particularly attractive crystallization in my estimation as the crystals grow above the level of the blue glass. This is of course more noticeable where the glaze is thin with 1-dip leaving little remaining glass.

Most glazes show a level of crystallization which rises with slow-cool time.

When the crystallization is ugly, I can usually make it a new and interesting slow-cool glaze by adding more glass and flux, with 10% Ferro Frit 3269, or 5301, or 3134.

 

This is another example, the zinc-fluxed Janet DeBoos Teal - fast-cooled and slow-cooled at our schedule of 50 F.  In this case I prefer the slow-cool. But it all depends on what you want.

After trying a number of slow-cool schedules, I decided on the one we use currently and have developed and adapted all of our glazes to be interesting at the schedule we chose to create our studio's look.

Rarely someone wants a Cone 6 without a slow-cool so we sometimes fire that as well.  Slow-cooling can "cure" crazing, so a beautiful crackle glaze comes out without crackles.  I've not been able yet to create a slow-cool version or Laguna Clay's "Tang Lime" crackle glaze, but I'm getting closer by increasing the expansion and reducing the kaolin in the original recipe. So that is one glaze that still generates request for an occasional no-slow-cool firing.

With your own kiln you have a lot more flexibility and freedom.

This photo shows a macro-crystalline glaze fired to Cone 6 with our slow-cool. Then subsequently refired in an 1,888 F bisque. The second bisque firing simply provides additional time in the 1,500 to 1,800 F temperature range, so the small areas of zinc silicate crystals grow to the entire area of glaze.

Brenda B Hardt said:

Norm- Thank you so much for this important info about flocculazation which I will set aside time to really understand and digest.

 I appreciate the warning about the WaterColor Green not liking your  slow cool schedule so guess I can plan to keep Warm Jade and Clear Blue and other glazes in a separate firing than my Stephen Hill glazes.

I wish I new my Skutt kiln well enough to know what to do.  Based on what u told me, here's what I will try as I have several pieces with Warm Jade and several with Clear Blue(with Minspar) in this load.  Wish me luck.

200/hr to 240F

100/hr to 500

450/hr to 2100

100/hr to 2170  (SH range 2160 to 2190)

cool to 1800, 50F/hr  HOLD 30 min

to 1700, 50F/hr Hold 30 min

to 1600, 50F/hr hold 30 min

to 1500,  50F/hr, no hold. Kiln off.

That would be a 8 hour COOL DOWN period. hmm?  you said 6 hour was your schedule.  I'll hold off firing until I hear from you again, if you are willing.

[Norm Stuart]

If you add a glaze flocculant and it doesn't work as expected, there's likely a reason for that.

I've added these glaze flocculants (suspending agents) to "Our Materials" in the Insight-Live database.

Please let me know if there is something missing from this list of contraindications. I'm sure it's far from complete.

(Click on the screenshot below to see it full-size)

[Norm Stuart]

Ammonium Sulfate appears to be an ideal flocculant to keep glazes suspended.

It's widely used in biology labs to flocculate proteins and costs less than $2.50 per pound on Ebay with free delivery.  So I bought some to try out.

1.)  It burns-out completely in the kiln, leaving nothing to alter the glaze chemistry.

2.)  I've found it's really effective flocculating kaolin in similarly small quantities to epsom salts or calcium chloride which add magnesium and calcium to the glaze.

3.)  Unlike Vinegar which has a pH of 2.4 and breaks down carbonates in glazes into a foaming mess, making them soluble - Even the most concentrated solution of Ammonium Sulfate lowers a neutral glaze pH of 7 only to 6, which is still very neutral leaving carbonates unaffected.

4.)  It's a plant fertilizer, a food additive, and a flocculant which is very inexpensive as huge amounts are produced in the process of making nylon fibers.

Please note you need Ammonium Sulfate, not nitrate.

[Norm Stuart]

Weathered Bronze Green normally settles badly due to being 60% nepheline syenite, 20% strontium carbonate, 20% Ferro Frit 3269,  9% silica with only 10% kaolin.

Since we've started using ammonium sulfate crystals to flocculate glazes I've seen the first interaction.

The Weathered Bronze Green remains suspended pudding thick from the spoonful of ammonium sulfate I added, and it fires the same.

But a thin layer of dark blue liquid formed on the top of the glaze most likely (Copper Sulfate Pentahydrate), leaving the pH of the glaze more neural, previously being slightly acidic.

This is from the "Copper Carbonate" (which is actually a combination of copper carbonate and copper hydroxide).

http://digitalfire.com/4sight/material/copper_carbonate_basic_236.html

This leaves the gelatinous Copper Hydroxide.  The glaze is still flocculated by the Ammonium ions with a +1 charge which when dry would now become part of Ammonium Carbonate, a baking powder known as "bakers ammonia".

With a Ksp (solubility constant) of

moles per liter at room temperature, only 1 mg dissolves in 8,000 liters of water, nearly insoluble, so the reaction proceeds very slowly.

If I've done the math correctly, it's something like this:

The simplest ion Copper (from the Copper Carbonate) forms is the odd complex of one copper molecule with 6 water molecules, in total having a 2+ charge.

The gelatinous Copper Hydroxide, freed from the copper carbonate, might further react with some of the ammonium ions to form and even darker blue Schweizer's reagent, which cellulose dissolves in. This is useful when making cellophane or rayon. But not being a proper chemist this is just a guess.

In our kilns all of the organic ions, ammonium and sulfate, burn-off as gas in any event.

Dry hydrated copper sulfate crystals   CuSO4·5H2O     The blue liquid is this color.

[Sharon Canfield]

How do you make up a concentrated ammonium sulfate mix to use as a flocculant? ie how much water to ammonium sulfate? Does it dissolve in cold water?

[Norm Stuart]

Ammonium sulfate and calcium chloride are both hygroscopic which means they readily dissolve in the moisture they absorb out of the air.

Left to it's own devices in an open container ammonium sulfate becomes a jar of water with 40% ammonium sulfate by weight.

Aluminum chloride also quickly absorbs moisture from the air, so I prefer to keep both in air-tight containers and add a pinch of dry powder to glaze as needed.

[Sharon Canfield]

Thank you Norm for that explanation!