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Dealing with wollastonite lumps


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Wollastonite is a major component of many of my glazes, but I hate the lumps that it forms, making sieving more difficult.  Does anyone have any tips on dealing with wollastonite lumps?

Things I've tried:

1)Extensive mixing with paint mixer on electric drill - not much help at all with reducing lumps

2)Stick Blender - can work okay on thinner glazes, but too much cavitation with thicker glazes for it to be effective.  (Most of the glazes I am making are brushing consistency.)

3)Putting the dry glaze ingredients in a zip lock freezer storage bag, removing most of the air, laying it flat on a table, and using a rolling pin to roll out lumps.  This is what I'm doing currently, and it works fairly well, but is rather time consuming.  When I weigh out glaze components I add them to the gallon freezer bags as I go, so I already have the dry glaze ingredients in the bag.  Next time around, I'm planning on weighing out the wollastonite first and then using the rolling pin technique on it before weighing and adding the other ingredients.

Does anyone have a better approach for dealing with this lumpy material, preferably without needing a ball mill?

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Hmm, never noticed any issue with wollastonite actually. Stick blender for small test samples and drill mixed / sieve for 7000 gram. They all seem to stay pretty workable in a dipping bucket. I wonder if it’s just the wollastonite or a combination of ingredients?

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Wollastonite agglomeration is a nuisance for me too. I find the older my supply is the worse it gets so I just buy a single 50lb bag at a time. Only thing I've found that cuts down on sieving time is whizzing it in a blender (with some of the glaze mixing water) does help. My main glazes have about 15% of it, takes a few batches to get it all whizzed up and scrape out the blender but saves sieving time in the long run. Even so I usually have a teaspoon or so left in the sieve (I use 80 mesh) so I have gotten in the habit of just adding an extra little bit when I weigh it out. It would be good to hear if anyone has a faster solution.

Edited by Min
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I have not tried this, but is this something that could be addressed by calcining it? I use zinc oxide and certain frits that are hydroscopic, causing them to chunk up in the bag/bin. I calcine them to around 900F to remove the moisture but not so hot that they begin to sinter. Then I spin them through a coffee grinder to reduce the chunks back to powder. Just an idea...

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I don't recall that wollastonite is especially hygroscopic, at least not to the point that zinc oxide is. Wollastonite has a needle like crystal structure that causes clumping. Stick your hand in a bin of wollastonite and grab a handful with your fingers pointing downwards. It won't flow out of your hand the way other materials do. It's almost like the wollastonite has loosely velcroed / clumped itself together.

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I do wonder if it’s mildly hygroscopic. It takes me a little persistence with an 80 mesh sieve, but it’s not something I find I have to compensate for a whole lot. And my area is mostly pretty dry.

I also try and slake glazes for at least 4 hours before sieving, if not overnight, so I don’t know if that effects anything or not.

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So just at a quick search, no it’s not hygroscopic. Like, at all. There’s a bunch of papers on it’s inclusion in plastics and cements that are either valuing it for its non-solubility in water, or mentioning that it needs HCL to dissolve. But we’re not looking to dissolve it, we’re just looking to disperse it.

So then just in a brain dump of ideas, would slaking the material in some epsom salt solution help lubricate it, especially if you were going to add some to the glaze anyway? Or a drop of darvan?

I might just go measure a little out right now to see what happens…

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@Piedmont Pottery  @Callie Beller Diesel @Min

sometime way back I was working with some calcium silicate materials as part of a glaze research project.  The problem was how to prevent the calcium silicates forming "concrete" from the glaze slurry sitting still for several days.  The answer came from a Professor researching concrete; very small amounts of sugar are often added to the concrete mix when the pour is more than an hour from the mix station to the pour sight;  using that data, and a SWAG adjustment from a an hour to "forever", a 10-12% sugar level (of the glaze solids) was arrived; the two gallons of glaze slurry with 10-12% sugar was still just a slurry (settled as soft and easily stirred without needing screening) after a several months setting in the glaze room.      

LT
 

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Thanks Lou, interesting stuff. So it's the hydration aspect that comes into play with sugar then? I was wondering about the flocculation that you had with your experiment so I googled sugar + flocculant and it turns out there is a flocculant added to cane sugar processing,  I'm taking one of your SWAG's and thinking that is going to have a minimal effect on flocculation though, if indeed it ever was used in the sugar you used.

Edited by Min
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My experimentation got delayed on account of needing to call for a hot water tank replacement :(. But that situation has now been dealt with. So. Onward!

I have weighed out some 20g samples of wollastonite, combined them with 20cc’sof water. 1 sample has 5cc’s of saturated epsom salt solution, 1 has a few drops of darvan 7, one has 5g  Roger’s table sugar plus an additional 5 cc’s water,  one has 2.5g Roger’s table sugar plus an additional 5 cc’s of water. Plus a control.

The plan is to slake them for 8 hours, and compare by weight any sieve residue, and to compare time and effort to sieve through an 80 mesh test sieve.I can’t really quantify effort with numbers, so that’s going to be more of a subjective observation on my part. 

I’ll try and report back around 9 pm Mountain time, but if I can’t get it written up tonight, look for it Sunday.

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Quick update for the curious: the sugar worked surprisingly well, but I think there’s a “sweet spot” to be had between too little and too much. Epsom salt was a runner up, and Darvan was not it.

I left it a little longer to slake. More like 9.5-10 hours rather than the intended 8, but life was interfering with other plans. I’ll do a more thorough write up on Sunday.

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This paper seems relevant, a one-line summary is:
... sugar not only alters the rate of cement paste hydration, but the microstructure of calcium-silicate-hydrate (C-S-H) as well.

New insights into the effects of sugar on the hydration and microstructure of cement pastes
Can be downloaded (hopefully securely!) from:
https://fdocuments.in/download/new-insights-into-the-effects-of-sugar-on-the-hydration-and-microstructure
The effects of adding sugar to cement paste on hydration and microstructure were observed. While 1% sugar delayed hydration as expected, the delay period was shortened by increased curing temperature. When samples containing sugar began to react, hydration progressed very quickly and the degree of hydration soon surpassed that of control samples. Sugar addition increased the surface area and altered the pore size distribution, as measured by nitrogen, of cement pastes. Results indicate that sugar not only alters the rate of cement paste hydration, but the microstructure of calcium-silicate-hydrate (C-S-H) as well.

PS I'll also give a couple of tiny quotes from another paper:

Reactions and Surface Interactions of Saccharides in Cement Slurries
https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.464.7279&rep=rep1&type=pdf

Specifically, sucrose is stable in alkaline cement slurries and exhibits selective adsorption at hydrating silicate surfaces ...

In the presence of additives such as saccharide molecules,cement hydration is known to be even more complicated.

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On 9/3/2021 at 10:42 PM, Morgan said:

Do you use a talisman rotary sieve? That is one of the better tools in my studio that saves me god knows how many headaches when glaze making. 

No, I don’t. Most of my glaze batches aren’t large enough to warrant one, nor do I have the storage space for it in an 11’x11’ studio. Also, for a lot of people who don’t make pots professionally, they’re an investment, and we do have a number of folks like that here that need low tech alternate solutions. So this line of experimentation might be more for them.

 

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So the experiment is complete, although like most good experiments, it raises some avenues for further exploration. 

First, a bit more on my methodology. After weighing and slaking my samples as above for probably closer to 9.5-10 hours, I used a stiff round and flat paintbrush to first stir the sample in the cup, pour it into the sieve, and scoop as much of the sample out of the cup as possible without adding any additional water. I then started a timer to see how long it took to sieve each sample. I pushed as much material through as I could. After wiping the excess off the bottom of the screen into the receptacle, the sieve was then weighed to see how much residue was left. The sieve was then washed and dried, the brush was rinsed thoroughly, and I moved on to the next sample after recording observations and results. Here are my observations.

Control sample:

Sieve Time: 54.05 seconds. Sieve Residue: 9.3g

Sample before sieving contained small, distinct grains and resisted being scooped out of the corners of the cup. The solids were heavily agglomerated in the bottom of the cup. It definitely took some effort to get it through the sieve, and would certainly require a second trip through the sieve for me to be satisfied that the material was thoroughly incorporated into a glaze. Sample was quite viscous.

 

Second Sample: 50cc Saturated Epsom Salt solution:

Sieve Time: 28.51 seconds. Sieve Residue: 4.4g

Sample before sieving still contained small grains, but flowed easily through the sieve with mild effort.There was some residue in the corners of the cup, but they were easier to dislodge than the control. Most of the sample flowed through the sieve on the first pour, and there was very little residue in the cup, most of it very fluid.

Third Sample: Rough Measure of Darvan 7 (4-5 drops)

note: I don’t own an eye dropper which would have made measuring the darvan easier.

Sieve Time: 1 minute, 2 seconds. Sieve residue : 5.2 g

Sample before sieving was pudding-like, with tiny distinct grains. The sample showed tendency to gel, and flowed better with some agitation. This sample had the fewest distinct grains in the sieve residue, but definitely was a lot more difficult to get moving. Would not recommend this addition if you’re looking to reduce your sieve time.

Fourth Sample: 2.5g Rogers Table Sugar (processed cane sugar) + 5cc water

Sieve Time: 16.71 seconds. Sieve Residue: 2.3g

Sample felt a little clumpy on initial stir, but loosened easily and left no residue in cup corners. Little effort to sieving, lumps broke up easily. The sugar is definitely a thing!

Fifth Sample: 5g Rogers Table Sugar +5cc water

Sieve Time: 31.46. Sieve Residue, 4g

Apparently there can be too much of a good thing though. This sample still poured readily with no clumping, but the solids wanted to ball up in the sieve in a way that none of the previous samples did. 

 

So there is definitely something to the idea of adding sugar or epsom salt solution to glaze batches that might have issues with Wollastonite agglomerations. Because sugar is going to have issues with rotting and stinking, my inclination would be to use the Epsom salts for some improved results. But sugar could possibly be an option if one were to add some copper carbonate as an antimicrobial, in the same way you would if you use cmc gum. Some fine tuning might also be necessary to get the amount right, as noted with the sample with the larger amount of sugar.

 

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1 hour ago, Callie Beller Diesel said:

Because sugar is going to have issues with rotting and stinking

I don't remember there being any "rotting" or "stinking" in the container that set in on the shelf for several months after my testing

placing a stick of bare copper wire in the container will be a deterrent on "rotting and stinking". 
LT

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I can see it not being a big issue if the sample is left undisturbed, and there’s limited opportunity for other bacteria to be introduced. Sugar is a preservative, after all. But even soda will grow mould if left open and bacteria is introduced. 

If you accidentally dump your old sponge into your glaze bucket instead of the rinse water next to it on glaze day, I could see some interesting new things growing in there a few weeks later.

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On 9/3/2021 at 9:42 PM, Morgan said:

Do you use a talisman rotary sieve? That is one of the better tools in my studio that saves me god knows how many headaches when glaze making. 

Agreed that for volume glaze mixing a rotary sieve is great, be it a Talisman or using a slow speed drill with a brush attachment but I haven't found it helps with the wollastonite issue. Gritty bits of it get stuck between the bristles and around the edge of the mesh that still need working through the sieve with a bit of water and a spatula or some such thing.

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So, from your experiment, it sounds like an addition of table sugar in the amount of 25% the weight of the wollastonite in the recipe will "solve" the clumping? For example, a recipe containing 10% wolly in a 5kg batch has 500g of clumpy wolly. Adding 125g of sugar (about 3/4 cup, one tablespoon weighing 12.5g per Mme Googlefu) will make that recipe fly through the sieve?

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3 hours ago, Dick White said:

For example, a recipe containing 10% wolly in a 5kg batch has 500g of clumpy wolly. Adding 125g of sugar (about 3/4 cup, one tablespoon weighing 12.5g per Mme Googlefu)

I'm getting different math using Callies best result figures of 20 grams wollastonite + 2.5 grams of sugar. I think you are using the higher amount of sugar figures that didn't work as well?

20 grams of wollastonite + 2.5 grams of sugar, multiply the 20 grams by 5 to bring it up to 100. Multiply the 2.5 grams by the same amount (5) brings it up to 12.5  So for each 100 grams of wollastonite it would be 12.5 grams of sugar. Therefore 500 grams of wollastonite would require 5 X 12.5 which would equal 62.5 grams.

Using your Googlefu weight of one tablespoon weighing 12.5 grams that would be 5 tablespoons sugar per 500 grams of wollastonite. 

It's late and I could have messed this up so double check my math.

Edited by Min
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3 hours ago, Min said:

Using your Googlefu weight of one tablespoon weighing 12.5 grams that would be 5 tablespoons sugar per 500 grams of wollastonite. 

Seems right to me,

It may be effective at much lower amounts if you continue testing. 12.5% at this point seems to be a new maximum needed. Nice work!

The use of sugar as a retarder in concrete is generally up to .06% by weight BTW. At roughly over .08% it starts to become an accelerant. 

Edited by Bill Kielb
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4 hours ago, Min said:

[ yaya, whut she said...]

My bad, yes, I used the the wrong sample, the 5g item. Your math is correct, so if it's 2.5g of sugar per 100g of wolly,  that hypothetical bucket of glaze would need 3/8 cup of sugar to sweeten it. Even that seems like a lot sugar to put in the bucket. Now that the idea is out, I can do some "line blends" as I mix new batches for the students...

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