Low specific gravity but THICK!

[Callie Beller Diesel]

Just to add to your joys, 

I’m assuming you’re using the recipe from John’s website, which is 

JOHN’S 10 x  12
Cone 6 (oxidation)

10.00   Custer feldspar
10.00   Spodumene
10.00   Silica (200 mesh)
10.00   Silica (325 mesh)
10.00   Talc
10.00   Whiting
10.00   EPK
10.00   Ball clay
10.00   Frit 3134
10.00   Frit 3195

Add:
5.00 % Mason Black Stain #6600

 

Some spodumenes are produced in part by floating them with a detergent. Some sources will create foam in the bucket, and you either need to wash it, or calcine it at 500-600 F, according to this digitalfire article.

Also, both frits are slightly soluble, which could lead to flocculation over time. Ball clays tend to be more subject to flocculation than kaolins, due to their particle sizes and shapes. With all of those factors, I would have been very surprised to see this recipe NOT gel at such a high SG as 1.53. Correcting it so it applied properly with water was the right move though, IMO. You got the application and end result you wanted. The reason you got cracking after that is more likely because of the clay content. Combined, that’s 20%, which can be a big high. Because you can’t really remove clay without affecting silica or alumina levels, you could either just use 20% epk (shrinks less when it dries than ball clay), or calcine half of the clay before adding it to your recipe.  

 

 

[Callie Beller Diesel]

32 minutes ago, Pir said:

is Darvan more or less effective in thinning different types of glazes?

Technically it does something chemically different than sodium silicate that gives a similar seeming result. 

Sodium silicate has a much smaller window in between where the glaze is only partly flocculated and suspends nicely, and turning into pudding. Especially if you’re using small batches of 500g or less, you’re pretty likely to goop your glaze by using it.

Darvan has a wider window, so if you accidentally add a bit too much there’s a bit more leeway, and you can rescue the glaze by adding more dry mix and water in the right proportions. Using either one, you need to mix very thoroughly between tiny additions.

If you want a nice deep dive into specific gravity and adjusting how glazes flow (or don’t) in the bucket, you can’t beat Sue McLeod. She’s a got a number of incredibly useful blog posts explaining it all here. 

[Pir]

Hi Callie, Thanks! I'm using John's 10X from the mid-fire book, but I've recalculated (lacking talc):

Dolomite 10 / frit 3134 10 / frit 3195 10 / custer 10 / EPK 10 / ball clay 10 / Si 16 / spod 10 / Mg CO 6.5 / woll 10 / stain 6600 5 / bent 2 (these are all rounded numbers).

3 hours ago, Callie Beller Diesel said:

Because you can’t really remove clay without affecting silica or alumina levels, you could either just use 20% epk (shrinks less when it dries than ball clay), or calcine half of the clay before adding it to your recipe.  

Worth a shot. Thanks for the McLeod link, I've listened to her before. 

So if you goop a glaze is it gone for good?

[Callie Beller Diesel]

On 10/21/2022 at 7:37 PM, Pir said:

So if you goop a glaze is it gone for good?

In theory you could rescue it, but if its a small batch, you’re better off tossing it and starting again. 

[Min]

@Pir, I'ld get rid of the bentonite with that recipe to start with, once you get the specific gravity at a level that gives a good glaze coverage and it's still too thick then the next step I would do would be to calcine most of the epk, I'm not seeing this as a recipe that would need a deflocculant at all. 

I just plunked your altered recipe into Insight, the silica is a fair bit lower in your version, need to bump it up from 16 to 24 then retotalled to 100

 

[Pir]

54 minutes ago, Min said:

@Pir, I'ld get rid of the bentonite with that recipe to start with, once you get the specific gravity at a level that gives a good glaze coverage and it's still too thick then the next step I would do would be to calcine most of the epk, I'm not seeing this as a recipe that would need a deflocculant at all. 

I just plunked your altered recipe into Insight, the silica is a fair bit lower in your version, need to bump it up from 16 to 24 then retotalled to 100

 

Min, I use Glazy--is Insight different? I see on Glazy that while the two formulas show identical quantities of oxides, the ratios are off. That's always confused me.

[Min]

47 minutes ago, Pir said:

Min, I use Glazy--is Insight different? I see on Glazy that while the two formulas show identical quantities of oxides, the ratios are off. That's always confused me.

My bad, I had a typo entering the recipe. 

Post a screenshot of the recipes so we can see the ratios. 

[Pir]

25 minutes ago, Min said:

My bad, I had a typo entering the recipe. 

Post a screenshot of the recipes so we can see the ratios. 

 

 

Edited October 24, 2022 by Pir

[Min]

Callie has the recipe above with silica at a total of 20 (10 325 mesh + 10 200 mesh), your original recipe has the silica at 10 plus custer instead of G200 which ones do you want me to use?

edit: I think this is why my silica level was higher

Edited October 24, 2022 by Min

[Pir]

Hi Min, I'm not sure why I used Custer--probably I was out of G200 (now I do have F4, or minspar, which I think is a sub). I use 325 mesh silica--because that's what I bought, not because I have experience using other meshes. Mesh along with calcining materials are, thus far, outside of my experience range!

What were you looking to do with the recipe?

This version of satin black works okay, except on some clays it leaves the impression of crack lines (which I'm understanding from previous comments as a manifestation of the clay drying--someone suggested using all EPK, as it's quicker to dry than ball). I haven't really tested it with cutlery or acid to see about leaching--these are also things I haven't quite built into my glaze testing habits yet. In other words, aside from the viscosity (at 153 SG), it seems like a well-behaved glaze (after a little Darvan and a splash of water). But perhaps the G200 would alter things; or the extra silica, as you're suggesting.

Did you have any idea about why the Glazy quantities looked the same but the ratios looked different?

Is Insight better software? Is it open to use?

 

 

 

[Min]

45 minutes ago, Pir said:

Is Insight better software? Is it open to use?

Whichever one you are comfortable with is the one I would use. Insight isn't free.

46 minutes ago, Pir said:

Did you have any idea about why the Glazy quantities looked the same but the ratios looked different?

 

It's just fine tuning the math, round up or down by the hundredths and you can get the ratios exact. I don't know to which decimal point Glazy will go to. Probably not significant.

Yours is the first in the screenshot below, fine tuned in the second to have the ratios exact and supplying the magnesium from magnesium carb, you can compare it to your altered recipe and see the tiny differences. Data into the materials database could alter slightly between software, in most cases it won't be significant. Extra 10 silica like in the original Britt recipe would likely gloss up the glaze somewhat. Notice the LOI has increased from 7.7 to 10.9, likely because of the magnesium carb. 

 

 

[Pir]

17 hours ago, Min said:

Extra 10 silica like in the original Britt recipe would likely gloss up the glaze somewhat. Notice the LOI has increased from 7.7 to 10.9, likely because of the magnesium carb. 

Thanks, Min.

LOi is something  I've largely ignored, being so occupied with learning so many other glaze things! 

Just to be clear, the John 10X original I got from the Mid-Fire book, and it has only 10 Si. I wasn't sure if you were saying there was another version with 20? Anyway, I'd be interested to see what a slightly glossier satin would look like. Perhaps like a piece of water polished black jade (one can dream!).

Pir

 

[Callie Beller Diesel]

I copied and pasted the recipe from John’s website. I don’t have the book to hand to compare. He uses 2 different mesh sizes of silica in the website recipe for a total of 20%. The website version uses whiting instead of getting the calcium from wollastonite, which also affects silica levels significantly. And probably LOI values. 

LOI is worth noting if your glaze is pinholing, but if it isn’t, you don’t have to borrow trouble. 

The silica thing would definitely affect gloss though. And glaze fit.

 

[Pir]

Here's another thick glaze I needed to recalculate for lack of talc.

I mixed a 2x sample, let it sit in water overnight, next morning it was peanut butter. Could ball it up with fingers. I added just enough water to get it to flow into a beaker to measure specific gravity--the SG is 120! Britt's rec for the glaze is 160 (book)!

Darvan doesn't do much. More?

Next day I add to the glaze  another 2x, dry, and that gets me to 150, still very thick or viscous. Darvan still doesn't do much.

I finally added water, 138 SG, applied much better. So... 138 fluid glaze vs 150 gelled glaze...? We'll see how the test pieces compare ...in some weeks... I don't have my own kiln yet  : ( .

 

[Min]

 I'ld replace the gerstley borate with a boron frit to supply the boron as gerstley is notorious for gelling glazes. Given that this glaze has only 10 clay you might then need to add 2 bentonite to it given it has a large amount of nepheline syenite and the frit.  Magnesium carb can actually flocculate a glaze but given there is only 3% that might not have this effect. How are you measuring your specific gravity? Is your scale tared out and accurate? 

[Pir]

Yes, scale good, and I'm careful with measuring.

That gerstley again! I've got a few frits I can look into...

10 clay... I thought adding bentonite would be superfluous because of the ger bor and EPK... i.e. other things keeping things in suspension...?

[Min]

If you replace the gerstley with a frit then you have a few things that like to sink to the bottom of the bucket, nepheline syenite being a big one plus the frit plus the silica. 10 epk might not be enough to suspend them. 

[Callie Beller Diesel]

If you’re testing anyways, try mixing your fritted version without the bentonite and see if it’s actually needed or not. Frit 3134 for example is slightly soluble, if less so than GB. If you use that as a substitute and increase your clay to make sure the alumina stays at the same level, bentonite may or may not be necessary. It will give you information either way, and you’ll get more of a feel for some of your materials. Using bentonite when it isn’t necessary in your own studio is a waste of materials imo.

 

When you say your darvan isn’t working on your how long are you mixing it in? Are you giving it just a good stir with a paddle, or using some sort of mechanical means?

[Pir]

Hi Callie, I haven't tried substituting with frits, yet. I assume I'd look at the various dominating ingredients in various frits and pick one matching the material I'm subbing it with, and then just tinker with the software.

Britt's book calls for bentonite in nearly every recipe, I think.

I've only mixed in Darvan in small batches, like 500ml. And I whisk the heck out of it. I could see how a couple of swirls with a paddle in a 5-gallon bucket might not do it, but I'd be surprised if I was getting the Darvan mixed in well enough in these small batches... But then, I've been surprised before.

Edited October 27, 2022 by Pir

[Callie Beller Diesel]

If you’re trying to substitute in frits for gerstley borate, the 2 main ones people use in North America are Ferro 3124 or 3134. 3124 was made to be a borocalcium supply similar to GB. It’s not exact, but it gets you pretty close. 3134 is almost identical to the 24, but it has most of the alumina removed. Among other things, this means you can source the alumina from added clay to help with glaze suspension. While they’re a great deal less soluble in the bucket than gerstley, the frits are still somewhat soluble, and the water on top of your glaze will be brown. Glazes with these frits shouldn’t gel, but it depends on ratios. You might not want to provoke the glaze application gods by adding bentonite unless strictly necessary.

With the darvan, time mixing does seem to matter. Thorough hand whisking will work for small batches, but you should try and sustain it for a good 60 seconds. Others may suggest longer. Big buckets I wouldn’t do without at least a drill/paint mixer combo for 3 minutes at least.. 

[Pir]

Hi Callie, thanks for the frit info. I'll try my egg beater on the next attempt to add Darvan. And I do have a drill and mixer, so I'll be sure to use that. 

P

[Min]

@Pir, looks like you already have a couple frits that contain boron, ferro 3134 and ferro 3195. Given that it's the boron you will be using a frit to replace the gerstley borate with just use what you have, can make the formula work with either.

Re my comment about might needing to add bentonite, look at the screenshot below, original is first recipe Jack's Green Matte, with ferro 3134 altered 1 and with ferro 3195 altered 2. See how little clay there is if you use ferro 3195, it's just at 6.33, this would be a good example of why bentonite would be needed. Using ferro 3134 gets the clay up to almost 16 therefore no bentonite needed in that version. Tiny differences from the original to the others, don't think they are significant in any way.

[Pir]

Here's another floc/defloc question, if anyone's still checking in (thanks again for all the generous advice!!):

From Pinnell's article, https://www.claytimes.com/articles/glazeadjusting.html 

"In addition, when clay is in a deflocculated state, it settles into a structure not unlike a deck of cards: parallel to each other and tightly packed together...a deflocculated glaze also acts differently when you apply it. When a pot is dipped into the glaze, the clay particles in the glaze will align into parallel layers on the surface, sealing off the pores of the bisque ware. .... A deflocculated glaze will stay wet on the surface, allowing the glaze to form a maddening number of drips and forcing the potter to stand forever waiting to put the pot down. At its worst, a deflocculated glaze will only go on in a thin layer and, when dry, will have a crystalline, drippy look...    When clay and water are in a flocculated state the clay has a structure like a house of cards: very open and porous. The result is that the glaze can build up quickly on the surface of the pot because there is nothing to impede the flow of water into the pores of the bisque. This becomes obvious when the pot is withdrawn from the bucket of glaze: the glaze coat will seem to dry almost instantly, with little or no dripping."

So, I just saw that my Leach Clear had settled and needed a bit of spatula work to unsettle (I mixed it up, too, and put it through an 80 mesh again). 

So, it was in a deflocculated state--the clay particles like "a deck of cards" atop one another. Now that I mixed it up, is it back in a floculated state, "a house of cards"?

Was the remixing enough to alter the attraction and structure of the clay particles? Or is some other step needed?

Thanks All.

Pir

 

[Callie Beller Diesel]

Having worked with Leach 4321 a bunch, it will settle out again if all you do is stir it. If you add a few drops of a saturated epsom salt solution and mix well, it stays suspended better. It also won’t form that charming rock-like layer if you have to leave the bucket sitting for a few weeks. 
Be very careful to only add small amounts and mix thoroughly before adding any more. You can gel the batch if you use too much. 

[Pir]

1 minute ago, Callie Beller Diesel said:

Having worked with Leach 4321 a bunch, it will settle out again if all you do is stir it. If you add a few drops of a saturated epsom salt solution and mix well, it stays suspended better. It also won’t form that charming rock-like layer if you have to leave the bucket sitting for a few weeks. 
Be very careful to only add small amounts and mix thoroughly before adding any more. You can gel the batch if you use too much. 

Thanks, Callie, but I'm also really trying to understand if the remixing (without additions) changes that "deck of cards" structure Pinnell mentions, i.e., from a dense deck (not good for absorption) to a porous house (good for absorption). In other words, if it looks mixed and suspended after having settled and been remixed, are the clay particles open, thus allowing quick drying? Or, can it look mixed and  suspended with the clay particles still being densely layered, thus not drying quickly?

I'm guessing/hoping that the mixing does change the clay particle structure for better absorption. I just wonder, if we go back to Pinnell's metaphor about dipping into a deflocculated glaze and getting the deck of cards structure, how one would even dip into such a settled glaze. What I don't want is to dip into a glaze that look good, but still get the dense deck of cards.