Low specific gravity but THICK!

[Pir]

Hi, I have made a number of glazes that are super thick, viscous, even as I add water and bring the specific gravity into the low 1.3s and 1.2s. At some point, does adding more and more water create a problem? I've been experimenting with sodium silicate--is this a solution to thinning glazes?  Are the others? I believe this doesn't affect the SG; are there other effects I might look out for?

Is there more to a thick glaze than high clay content, or something like lots of MgO?

Thanks for any advice,

Pir

Edited October 1, 2022 by Pir
repetitiveness

[Min]

Darvan is the go to for deflocculating a glaze, sodium silicate (plus soda ash) for deflocculating casting slip. There are other culprits for over flocculation of a glaze, bone ash or tricalcium phosphate is a big one, high amounts of red iron oxide and gerstley borate can both gel up a glaze. For glazes high in clay, like over about 15-20% it's a good idea to calcine part of the clay content, this reduces the amount of shrinkage of the glaze therefore reduces the chance of the glaze crawling. Having too low a specific gravity means there is an oversupply of water in the glaze, the more a glaze shrinks as the water evaporates the higher the chance of the glaze flaking off or crawling.

[Pir]

Thanks Min, I haven't tried Darvan yet. Didn't know that RiO can gel a glaze, too--though I've seen it with Ger Borate.

Thanks, Pir

[mr_glazy_man]

My only issue with Darvan is that if you don’t use all the glaze in that sitting after mixing, it will settle and brutally hard pan in the bucket. 

[Min]

1 hour ago, mr_glazy_man said:

My only issue with Darvan is that if you don’t use all the glaze in that sitting after mixing, it will settle and brutally hard pan in the bucket. 

That's interesting you found that, hasn't been my experience.

[Pir]

On 10/8/2022 at 8:23 PM, mr_glazy_man said:

My only issue with Darvan is that if you don’t use all the glaze in that sitting after mixing, it will settle and brutally hard pan in the bucket. 

That would be diabolical. My pint of Darvan is in the mail, so I'll find out soon! Thanks for the heads up,  mr_glazy_man.

[Callie Beller Diesel]

The trick with anything you’re using to increase flow in a glaze is to add only a bit at a time, and mix extremely well before adding more. I would venture that if your glaze has hardpanned with darvan, you’ve added a bit too much. 

 

[Morgan]

Look into thixotropy as well. Basically the last thing you want to do in glazes like this is to keep adding water. Get your SG where you want it and floc/defloc from there. What that SG should be is going to take testing with a glaze and simply knowing your glaze well/application

Great video that explains thixotropy in simpleton terms 

 

and this one more specific to your case
 

 

[Pir]

Thanks Morgan, before understanding flocs/deflocs, I was adding/removing water to attain what I'd hope would be a good viscosity, then looking at the SG. But this was confusing for glazes that came with SG recommendations. For example, in Britt's book,  John's x10 satin black--he suggests an SG of 1.55, I think, but the glaze was incredibly thick, like almost too thick to flow. Now I'm thinking that I should get that SG, but then deflocculate to get a thinner glaze... Does that sound right? And with clears, I kept watering them down to get them thinner, down to SG 1.20--which might fire clear but also make a gritty surface; so, would it be better to keep a higher SG and thin it with a defloc?

With test glazes with no SG recs, I was trying to start them all at SG 1.40 to see how they worked at this middle-of-the-road point. More recently, though, I'm just testing with a finger and feeling for a good viscosity; if it fires nicely, I'll use that SG.

But as you can probably tell I don't yet have this--the relationship between viscosity and SG and deflocs/flocs and water--totally under control. Should an SG be attained first, and then the viscosity altered with floc/defloc? Or is the viscosity more important to get, despite whatever the SG is? Is there some standard procedure or order of operations people use when testing a glaze?

Thanks again--and thanks for the videos. I watched those a long while back, but watching them again will make more sense this time, I'm hoping.

Pir

Edited October 12, 2022 by Pir

[Hulk]

Tony Hansen's articles and video clips on thixotropy were, err, are major factors in turning glazing around from sigh, ugh to Yeah! Whee (for me)!

I'm doing SG first, then thixotropy.

For me, adjusting SG relates to how fast I have to move:
  Wetter takes longer to build up desired thickness.
  Wetter takes longer dry.

I prefer not having to hurry the pours and dips, so, wetter, between 1.39 to 1.45 for my glazes, where more time is required to build up the desired thickness, more time to execute the glazing. A drawback is that I'm also waiting longer for the wet sheen to fade to the point where any drips can be smoothed in, etc., and overall, takes longer.

Once SG is dialed, then I'm adjusting thixotropy, which, btw, is not exactly same as viscosity.

I want to see the entire mass of glaze turning together when stirred, rotating just a few times once I stop stirring, then come to a stop all together, with that "bounce back" that Mr. Hansen points out.

Adjusting thixotropy ("gel") means much less sheeting and dripping.
Pouring out in a smooth, slow manner, then waiting a few moments (whilst running any drips at the edge around and around) afore shaking off drips yields a smooth application, no sheeting, no drips.
Withdrawing a dip slowly, then same waiting a few moments (whilst running any drips at the edge around and around) afore shaking off drips yields a smooth application, no sheeting, no drips.

Ohh k, less sheeting and drips (much less).

With lower SG, I don't have to hurry, can take more advantage of the "gelling" action.

When the glaze is moving, it behaves liquid; as the glaze stops moving, it behaves "gel"...

"...simpleton terms"
Yep. As interesting as the physics, chemistry, rheology, et cetera, are, adjusting SG and thixotropy can just stay simple.

 

[Min]

2 hours ago, Pir said:

Should an SG be attained first, and then the viscosity altered with floc/defloc?

Yes.

[Pir]

Thanks, Hulk.

1. "Pouring out in a smooth, slow manner / Withdrawing a dip slowly, then waiting a few moments (whilst running any drips at the edge around and around) afore shaking off drips yields a smooth application, no sheeting, no drips." I have generally been pouring out quickly and shaking like a madman, so I'll try it slow and see if that helps correct lousy applications!

2. So, lower SG = wetter (closer to the weight of water, less material in suspension), and higher SG = dryer (heavier than water because more material, less water)... right?

3. Okay, SG first, then adjustments for thixotropy... BUT, how does one know what SG to aim for? Hansen seemed to base it on the ingredients present in the glaze, but lacking that depth of knowledge (and lacking any recommendations offered with the recipe), what is one to do to determine SG? Take a 100-gram test batch of a new glaze: I have to add some amount of water, and that amount will determine the SG, after which I can adjust thixotropy (and judge it visually, by watching the turn and bounce back, by testing with tiles, etc), but that still doesn't tell me if I started with the best SG. Even retrospectively, I'm still unsure how to judge if the SG is "correct"--and what is a "correct" SG, anyway?

4. Does a "Correct" SG have to do with the amount of material that will land on a pot at some rate of time (like a 2-sec dip)? I think I confuse that with viscosity--which I'm probably confusing with thixotropy--that is, I'm thinking a very thick glaze (with no regard to SG) will get lots more material (sometimes too much) on a piece, and a thin glaze will get less on it.

Thanks, all!

Pir

[Bill Kielb]

23 minutes ago, Pir said:

4. Does a "Correct" SG have to do with the amount of material that will land on a pot at some rate of time (like a 2-sec dip)? I think I confuse that with viscosity--which I'm probably confusing with thixotropy--that is, I'm thinking a very thick glaze (with no regard to SG) will get lots more material (sometimes too much) on a piece, and a thin glaze will get less on it.

This might help - the desired sg is the one that works best for a glaze and an application method. Often it’s tested and recorded once known. I like a three second dip, others prefer differently. Additionally for a clear glaze for example I like them applied as thin as practical and with a uniform 100% coverage. So desired sg to me is dependent on what’s being applied and application method as well as desired thickness. In other words It’s usually a recorded number for a particular product based on experience

[Pir]

Thanks, Bill.  I guess it's more of a recursive, not a linear, process to determine the best SG. But I still wonder at how that "best" SG is arrived at. Let's say I mix a new glaze to 1.45, adjust for thickness (viscosity and thixotropy?) using Darvan or vinegar, and get a glaze that applies and dries to my liking. To my mind, my adjustments were made based on that 1.45 SG, but I'm missing the part that tells me that this was the best starting SG. Had I started with 1.40, my adjustments would've been different (more or less darvan or vinegar), right? 

And maybe there's some advantage (or disadvantage) to a 1.4 and X quantity of vinegar or darvan, as opposed to, say, 1.45 and some other quantity.

Maybe the answer is this: that whatever SG and adjustments one makes to arrive at a workable glaze is okay, so long as it can be repeated. So various SGs with  various quantities of floc/defloc can produce  similar results... But that doesn't sound totally right...!

 

[mr_glazy_man]

@Pir I would test at various SG if I were you. This will help you understand the differences between a heavier vs lighter SG. Get your SG to the right amount (always start at the heavier end) - say 1.5 - add your defloc, then do a dip. Add some water to 1.45, do a dip. 1.4 etc 

 

Getting the right SG from a glaze perspective means there is enough material on the ware to form a good melt, and from the colourant side of things, the right intensity of colours. It’s almost subjective - you’re the one that decides the right SG based on whether you enjoy the end result post firing. 

[Pir]

5 hours ago, mr_glazy_man said:

Get your SG to the right amount (always start at the heavier end) - say 1.5 - add your defloc, then do a dip. Add some water to 1.45, do a dip. 1.4 etc 

Thanks, mr_g_m. Having a repeatable procedure like that will be helpful.

 

9 hours ago, Hulk said:

With lower SG, I don't have to hurry, can take more advantage of the "gelling" action.

When the glaze is moving, it behaves liquid; as the glaze stops moving, it behaves "gel"...

So if it's wetter (lower SG), it won't dry as quickly, allowing more time to apply the glaze, and the advantage of the "gelling action" is that the glaze moves and covers the body as a liquid and then, thanks to thixotropy, stops as a gel. Okay, I think it's sinking in. Thanks again!  

...and if anyone wants to keep talking about it, I'm wondering if thixotropy can occur naturally in glazes (with the right materials) or is it only via a defloc?...

[Hulk]

Some of my glazes don't need any thixotropic adjustment, likely on account of the gerstley borate, so, yes on naturally occurring thixotropic, imo.

The clay absorbs water, hence the layer of glaze right on the clay gets the water sucked out and sticks on thar; "wetter" glaze - thinner layer given same exposure time.
A surface that isn't absorbent will also get thinner layer with a wetter glaze; looks to me that an absorbent surface multiplies the thickness difference per unit time tho'.

Do trials, keep good notes!

[Min]

@Pir, there is a really good Clay Times article by Pete Pinnell linked below that might help clarify the what's and therefores of flocculants and deflocculants. 

https://www.claytimes.com/articles/glazeadjusting.html

 

[Morgan]

Yes, almost all of my glazes I do not even mess with floc/defloc, in fact I try NOT to even go there but glazes that seem to gel like crazy even with a ton of water you need to. Some glazes are also a lot more picky about showing drip lines etc where thixotropic adjustment will help tremendously.

A big factor touched on above is how you prefer to do application. Long dips, multiple dips, short quick dips, spraying, brushing etc. I frankly do not like it much (or think its a tad misleading) when people put up a SG for a given glaze as it makes it seem like that is the exact SG you need. I get its a ballpark for most but I think it is misleading. For example I have some glazes that always get layered and so I tend to have that have a lower SG so my combined glazes do not get too too thick and crawl or flake off. 

Long and short of it is test and you will come to understand your glazes best SG, application etc and it will become second nature. I do not even really measure my SG I just know by the consistency and the results where to be. Of coarse you need SG if you plan on tweaking with floc/defloc. 

Once other tip: If you get a glaze where you want it after mixing up a batch, check it again every other day or so as some will gel up over time. I can tell by ingredients that I will get it roughly where I want it but by the next day it will need more tweaking.

[Pir]

On 10/13/2022 at 11:25 AM, Min said:

@Pir, there is a really good Clay Times article by Pete Pinnell linked below that might help clarify the what's and therefores of flocculants and deflocculants. 

https://www.claytimes.com/articles/glazeadjusting.html

 

Thanks, Min, I had actually read that at one time (it was bookmarked) but like so many things, it made more sense after some experience.

[Pir]

5 hours ago, Morgan said:

Once other tip: If you get a glaze where you want it after mixing up a batch, check it again every other day or so as some will gel up over time. I can tell by ingredients that I will get it roughly where I want it but by the next day it will need more tweaking.

Thanks, Morgan. Yes, I've noticed that some glazes gel up over time. Or they look like pudding but when stirred they liquify some (aka thixotropy)--but are perhaps still thick.

The drippy glazes: I think I usually associate these with thinner glazes (thinner might not be the best word), and have in the past used Epsom salts with some success to gel them (I'm hearing vinegar is better). But now that I think of it, some of those gelled glazes also dripped or sheeted (which seemed to defy logic)... So, I'm looking forward to my bottle of Darvan arriving!

 

[Callie Beller Diesel]

On 10/12/2022 at 6:54 PM, Pir said:

...and if anyone wants to keep talking about it, I'm wondering if thixotropy can occur naturally in glazes

Absolutely. There are a number of materials that are soluble, which affects thixotropy. Most boron containing materials (including frits!) dissolve in water at some rate. Although you’ll usually hear the most cursing about Gerstley Borate, even frit 3134 will kick in over time, although that one usually happens in a time span measured in months, not days.

Bone ash, soda ash, and larger amounts of red iron oxide can also be culprits. You don’t usually get a lot of cone 10 reduction glazes that hardpan the way high frit ones can, unless you do something like freeze them. 

[Pir]

Thanks, Callie, that makes sense now. The gelling is itself a manifestation of thixotropic properties (I think).

[Callie Beller Diesel]

It absolutely is. In a lot of scenarios, controlled thixotropy is something we take advantage of. Lots of people can describe it without knowing it has a technical term. 

[Pir]

I had some success with the Darvan (if anyone's still there!). One big question, front loaded  if you want to skip the juicy details below: is Darvan more or less effective in thinning different types of glazes? And is adding lots more--when it doesn't seem to be doing much--harmful? --I know sodium silicate is. Is there a point it just won't work?

Darvan was most noticeable in a glaze with 85% Alberta slip (and 10% RiO): 3-5 drips in 500 ml made a profound difference and a beautifully applicable glaze.

However, with a satin black (John Britt's x10: many ingredients but no dominant one--except, lacking talc, I recalculated it to include magnesium): 40 drips in 500 ml made it a little thinner (was a custard at 153 SG), but not as much as I'd like. This glaze also dries with "crazing" lines that do not fully rub off; on some (but not all) clays, these lighter lines are visible after firing. And ugly. I thought it was excess water in the glaze (which previously I'd added trying to thin it). But eventually I stopped dripping Darvan and thinned it with a splash of water, so SG went from 153 to 147--but that got me a relatively flowy, even, quickly drying glaze. But still the cracking.

Similar with another (red/brown) glaze (with 26% Ger Bor, 6% MgO, 15% RiO--all things I'm learning will gel)--Darvan didn't do much. Still pretty thick, but also (kinda?) wet, with an SG of 141, I tried a piece and got some bad streaking (sheeting? layering?) on a pour-out. So, more experimenting to do... more Darvan? Lower the water content (skimming it or adding a new batch of the same glaze).  ...It seemed to work really well with my initial tests when it was around 135, actually (but still thick).

If anyone's still reading this you must have the glaze fever, like me. A wollastonite (35%) glaze I made some months ago (w/ 40% ball clay) had 130 SG--no doubt because I had kept adding water trying to thin it. Consequently, a tiny bowl I applied it to took over five minutes to dry to the touch. So next time, a higher SG and some Darvan.

P