Glaze dripping

[Gonepotty]

Hi all, having a bit of a hard time with glaze application.
Recipe:

potash feldspar 33.    talc 21.    quartz  16.    china clay 15.    whiting 12.     zinc oxide 3.

recipe is quite thick and tends to settle easily on bottom of bucket. I have upscale this recipe to 12 000g batch so is approx 21L in the bucket .  S.G is 1.44. Added a bit of Epsom salts to help with the glaze settling.  Issue is, the glaze seems to run quite a bit when applied to bisque ware. As it’s quite thick it sends to run slowly and leave really thick streaking marks. (Image attached). Not really sure whether to continue flocculating, but will this make it even more thicker??, or deflocculate, or add water which will start to take the SG below 1.4.

any thoughts greatly appreciated.

Kathryn

Edited December 14, 2023 by Gonepotty
Amended

[Hulk]

Good idea to start with a test batch!

Did the Epsom salt addition make any difference at all?

My glazes, some require more Epsom salt (saturated) solution than others.
A few points in specific gravity can make a difference; I run as low as 1.41 (one glaze), high as 1.46...
...after an addition, stir, stir, wait, test, then give it some time before making another addition.

How to measure the "gel" - when has enough Epsom salt been added?
See Tony Hansen's video clip:
Thixotropy and How to Gel a Ceramic Glaze (digitalfire.com)
...stir the glaze at a repeatable and reasonable speed, then watch as the revolving mass slows and comes to a stop.
I look for three to four turns before the entire mass slows to a stop, then "bounces back" just a little bit.

Glaze that requires adjustments just keeps on spinning well past three or four turns, with currents of different speeds shearing against each other.

For pouring and dipping, slow and deliberate motion, particularly pouring out or lifting up.
A bit wetter glaze (lower specific gravity) allows more time to complete the glazing, but takes longer to dry.

Hope that helps, check back for more suggestions from others, and please do update on how it goes...

[Gonepotty]

13 minutes ago, Hulk said:

Good idea to start with a test batch!

Did the Epsom salt addition make any difference at all?

My glazes, some require more Epsom salt (saturated) solution than others.
A few points in specific gravity can make a difference; I run as low as 1.41 (one glaze), high as 1.46...
...after an addition, stir, stir, wait, test, then give it some time before making another addition.

How to measure the "gel" - when has enough Epsom salt been added?
See Tony Hansen's video clip:
Thixotropy and How to Gel a Ceramic Glaze (digitalfire.com)
...stir the glaze at a repeatable and reasonable speed, then watch as the revolving mass slows and comes to a stop.
I look for three to four turns before the entire mass slows to a stop, then "bounces back" just a little bit.

Glaze that requires adjustments just keeps on spinning well past three or four turns, with currents of different speeds shearing against each other.

For pouring and dipping, slow and deliberate motion, particularly pouring out or lifting up.
A bit wetter glaze (lower specific gravity) allows more time to complete the glazing, but takes longer to dry.

Hope that helps, check back for more suggestions from others, and please do update on how it goes...

I have added about 5 Tablespoons saturated Epsom solution to a 21litre batch and hadn’t made much difference to the drip marks but has increased the drying time. Doesn’t appear to be getting any thicker after adding Epsom solution and still spins for about 6 seconds or so. It is odd though because if I take about 1 litre in a small just and mix it up it stops after about 3seconds but in the large 21 Litre bucket it keeps spinning??? Which do I use ?

I have watched the video from Tony Hansen and added a tiny amount vinegar to a tester pot and this made no difference at all. If I get the SG down to about 1.36 then the drip marks seems to reduce but then won’t it be a deflocculate glaze if too much water is added?

[High Bridge Pottery]

So even in your smaller trials the glaze is the same thickness and settles out quickly?

 

Can't see much in the recipe to make it thick. Been a long time since I used zinc but I think that can thicken glaze but probably not at 3%, 15% china clay shouldn't thicken it that much either and be pretty good at suspending the rest.

[Gonepotty]

1 hour ago, High Bridge Pottery said:

So even in your smaller trials the glaze is the same thickness and settles out quickly?

 

Can't see much in the recipe to make it thick. Been a long time since I used zinc but I think that can thicken glaze but probably not at 3%, 15% china clay shouldn't thicken it that much either and be pretty good at suspending the rest.

Yes it also settles out in the trial glaze batch.  I’m also quite stumped as to why it has drip “flowing” marks. Perhaps it will be better if slightly thinner at a SG of 1.4? 

[Callie Beller Diesel]

Don’t get too hung up on specific SG numbers. The number that works is the one that gets the right application of glaze YOU want on your pot, and that might be different than what someone else recommends. The 1.4 mark is a rough starting point, kind of like seasonings in a recipe. Some people will want more, some people will want less. 

First, water is the easiest thing to adjust in a glaze, and adding things like epsom or darvan to adjust how a glaze flows should be done only after you’ve determined it’s really necessary for getting the right glaze application. If the bucket has a layer of glaze materials in the bottom within 5 minutes of mixing, pulling out the epsom salt solution is the right thing to do. 

Adding epsom salts will flocculate a glaze, or make it gel slightly. This is why the glaze now seems thicker than it did, and it may leave a more generous layer on the pot than the same 3 second dip would without the flocculation. You might notice on some glazes it will start to crack while drying, potentially causing crawling in the kiln. And yes, it will also slow your drying time. That slowed drying can help smooth out application based drip marks. If your glaze is one that might be subject to crawling due to application, adding water will help resolve that. But know that adding water to a glaze that’s already flocculated will further delay drying. It may mean you have to adjust your workflow to allow for that, but it’s worth it if it means the glaze goes on the pot nicely. 

Another question worth asking is whether or not any of your ingredients are soluble in the bucket over time. It’s usually more of a problem with boron containing materials, but some feldspars can be subject to this as well. Solubles can affect glaze application if they cause additional gelling. 

[Gonepotty]

40 minutes ago, Callie Beller Diesel said:

Don’t get too hung up on specific SG numbers. The number that works is the one that gets the right application of glaze YOU want on your pot, and that might be different than what someone else recommends. The 1.4 mark is a rough starting point, kind of like seasonings in a recipe. Some people will want more, some people will want less. 

First, water is the easiest thing to adjust in a glaze, and adding things like epsom or darvan to adjust how a glaze flows should be done only after you’ve determined it’s really necessary for getting the right glaze application. If the bucket has a layer of glaze materials in the bottom within 5 minutes of mixing, pulling out the epsom salt solution is the right thing to do. 

Adding epsom salts will flocculate a glaze, or make it gel slightly. This is why the glaze now seems thicker than it did, and it may leave a more generous layer on the pot than the same 3 second dip would without the flocculation. You might notice on some glazes it will start to crack while drying, potentially causing crawling in the kiln. And yes, it will also slow your drying time. That slowed drying can help smooth out application based drip marks. If your glaze is one that might be subject to crawling due to application, adding water will help resolve that. But know that adding water to a glaze that’s already flocculated will further delay drying. It may mean you have to adjust your workflow to allow for that, but it’s worth it if it means the glaze goes on the pot nicely. 

Another question worth asking is whether or not any of your ingredients are soluble in the bucket over time. It’s usually more of a problem with boron containing materials, but some feldspars can be subject to this as well. Solubles can affect glaze application if they cause additional gelling. 

It doesn’t settle as in rock solid but there is a thin layer of material sitting along the bottom within 5minutes.  I wonder if I have ruined the glaze batch by adding too much Epsom salts? It’s not overly thick at all…almost like single cream consistency. It seems that the 5 Tablespoons of saturated Epsom salts I added didn’t cause it to turn too thick/sludgy or make much difference to the consistency but still appears to have the very thick drip runs after a 3 second dip. 
All the ingredients stay dissolved in the bucket if that’s what you mean by the last question? - sorry I’m a bit confused by this question.

Thanks so much for your help 
 

[Hulk]

"Which do I use ?"

Hard to say.
I'm guessing the larger the container - the larger the mass of glaze - the longer it would spin before stopping, everything else being equal - perhaps due to more mass per unit surface area of the bucket interior, which provides the drag? Easy enough to test; mix thoroughly, pour some off to a smaller bucket, re-test.

My experience is with different glazes and two gallon buckets.
However, I've good results with tweaking the specific gravity and thixotropy of every glaze I've tried.
Two of my glazes I don't add any Epsom salt too at all; they gel great as is.

Added: 21 liters is just over 5.5 gallons, that's a lot of glaze
 

Edited December 16, 2023 by Hulk
batch size

[C.Banks]

22 hours ago, Gonepotty said:

I have added about 5 Tablespoons saturated Epsom solution to a 21litre batch

This sounds like a lot.

iirc for a 2000-3000 gram batch I was adding ? 20 ml's? which is ~1.3  tablespoons if one tablespoon equals 15 mls.

If I were trying to start from memory 10 mls per litre still sounds like a lot but I'm suspicious of anything from memory over a week old.

Edited December 15, 2023 by C.Banks

[Mark C.]

(This sounds like a lot.)

a tablespoon  or two is plenty for a 10,000 gram batch

5 tablespoons is way to much for 3,000 grams-it will be thick soup

[Gonepotty]

On 12/15/2023 at 4:17 PM, Mark C. said:

(This sounds like a lot.)

a tablespoon  or two is plenty for a 10,000 gram batch

5 tablespoons is way to much for 3,000 grams-it will be thick soup

Hi Mark, I have add 5 tablespoons to a 21L batch. 

[C.Banks]

10 minutes ago, Gonepotty said:

Hi Mark, I have add 5 tablespoons to a 21L batch. 

Hi Gonepotty,

I'll go back to lurking - better to remain silent and all that

[Min]

 

12 000 gram batch of glaze, made up approx 21 L which would be just over 4 1/2 Imperial gallons of glaze. Recipe contains china clay (grolleg?) at 15% so it shouldn't be hard-panning. 5 tablespoons of saturated epsom salts solution added but glaze slurry still leaving heavy drip marks. Typical amount of epsom salts solution would be in the range of 1 tsp per US gallon (0.8 of an Imperial gallon)

Has the efficacy of the epsom salts solution been tested? Have you tried a new saturated solution?

Is the method of dipping the pots part of the issue? Is this a clear glaze high fire? How are the drips with a lower sg? How does the glaze look when fired with a lower sg? 

[Mark C.]

2 hours ago, C.Banks said:

Hi Gonepotty,

I'll go back to lurking - better to remain silent and all that

No need for that keep asking questions and doing pottery as you will learn more and we can help

[Callie Beller Diesel]

On 12/14/2023 at 12:13 PM, Gonepotty said:

All the ingredients stay dissolved in the bucket if that’s what you mean by the last question? - sorry I’m a bit confused by this question.

Your saturated epsom salt solution is dissolved. Your glaze is a suspension*. 

Dissolved is not the same as suspended. Dissolved is like when you make a simple sugar syrup or saline: the sugar or salt particles become indistinct from the liquid. A suspension is when the particles stay distinct from the liquid it’s in, but stay more or less dispersed throughout.  A suspension may settle out over time, or be re-suspended when you stir it up. A solution won’t loose the original materials out of it, unless it changes temperature or some of the water evaporates out of it. 

*a glaze can sometimes be a combination of a suspension and a solution if some of the materials do actually dissolve into the water of the glaze over time. The boron in things like gerstley borate or some frits are known for being soluble in glaze buckets, as are a few other things. This process tends to take a few days or even weeks, and when it happens, the now-solution part of the glaze helps keep the other dry particles suspended. This is also called gelling or flocculating. When you add epsom salt solution to a glaze bucket, you’re either creating this effect in a glaze that has no (or negligible) soluble materials, or accelerating it in a recipe that has some solubles.

Unless your glaze has turned to the consistency of something like skyr or Greek yogurt, you have not ruined it with the amount of epsom salt solution you've added. Single cream is kinda sorta the ballpark of what you want a glaze consistency to start at, but you’re still having some settling. Your description of your glaze’s behaviour with the epsom salt says you might need to add more. But there’s some question about the amount you’ve already added. 

Is your epsom salt solution super saturated, or did you dissolve some in some hot water and go from there? A super saturated solution is made by adding Epsom to boiling water from the kettle until you can’t dissolve any more. You will need a surprising amount for this. There should be some crystals at the bottom of the container that won’t dissolve easily while still hot, and as the solution cools, some more crystals should appear at the bottom. The resulting solution will be clear, but will refract light in an almost oily way. It’ll also eat through metal lids over time, so if your storage jar has a metal lid, line it with a bit of cling film.

If your solution isn’t super saturated, that could account for the seemingly large volume not giving you the desired effect. If that’s the case, you do have some room to add more. You also have to mix quite thoroughly to give the effect a chance to work.

A cautious method to test if adding more would help or go too far is to remove a sample from the bucket and add flocculant to it by drops, mixing well between additions. 

 

[C.Banks]

So in the interest of clarity: 21litres can look a lot like 2 litres to tired eyes

...

[Babs]

Why not run some rest tiles?

Decant a known amount of your glaze. Add known increasing amounts amounts of water to a few cups, add known same amount of glaze to each cup. Dip test tiles., same tile in three different dips in same cup to test thickness  desireable. Fire.

It could be as "simple" as that.

Loks like yIur glaze wants to stck to itself no matter what.

If you get a result you like, maybe you can save the batch by adding the required amount of water, Or you could add a known amount of this espom salt rich stuff to a new batch and dont add any more epsom, if sone could do the Maths. Maybe @Rockhopper  he saved me in the past.

 

[Gonepotty]

1 hour ago, Callie Beller Diesel said:

Your saturated epsom salt solution is dissolved. Your glaze is a suspension*. 

Dissolved is not the same as suspended. Dissolved is like when you make a simple sugar syrup or saline: the sugar or salt particles become indistinct from the liquid. A suspension is when the particles stay distinct from the liquid it’s in, but stay more or less dispersed throughout.  A suspension may settle out over time, or be re-suspended when you stir it up. A solution won’t loose the original materials out of it, unless it changes temperature or some of the water evaporates out of it. 

*a glaze can sometimes be a combination of a suspension and a solution if some of the materials do actually dissolve into the water of the glaze over time. The boron in things like gerstley borate or some frits are known for being soluble in glaze buckets, as are a few other things. This process tends to take a few days or even weeks, and when it happens, the now-solution part of the glaze helps keep the other dry particles suspended. This is also called gelling or flocculating. When you add epsom salt solution to a glaze bucket, you’re either creating this effect in a glaze that has no (or negligible) soluble materials, or accelerating it in a recipe that has some solubles.

Unless your glaze has turned to the consistency of something like skyr or Greek yogurt, you have not ruined it with the amount of epsom salt solution you've added. Single cream is kinda sorta the ballpark of what you want a glaze consistency to start at, but you’re still having some settling. Your description of your glaze’s behaviour with the epsom salt says you might need to add more. But there’s some question about the amount you’ve already added. 

Is your epsom salt solution super saturated, or did you dissolve some in some hot water and go from there? A super saturated solution is made by adding Epsom to boiling water from the kettle until you can’t dissolve any more. You will need a surprising amount for this. There should be some crystals at the bottom of the container that won’t dissolve easily while still hot, and as the solution cools, some more crystals should appear at the bottom. The resulting solution will be clear, but will refract light in an almost oily way. It’ll also eat through metal lids over time, so if your storage jar has a metal lid, line it with a bit of cling film.

If your solution isn’t super saturated, that could account for the seemingly large volume not giving you the desired effect. If that’s the case, you do have some room to add more. You also have to mix quite thoroughly to give the effect a chance to work.

A cautious method to test if adding more would help or go too far is to remove a sample from the bucket and add flocculant to it by drops, mixing well between additions. 

 

This is such brilliant information - thanks so much for taking your time to help and explain. Really appreciated. I suspect the Epsom solution wasn’t saturated enough so I mixed up a new batch and this has helped a lot. Much better consistency and better glaze application. I’ll test a couple pieces in next firing.

thanks again

[Gonepotty]

1 hour ago, C.Banks said:

So in the interest of clarity: 21litres can look a lot like 2 litres to tired eyes

...

 

3 hours ago, Min said:

 

12 000 gram batch of glaze, made up approx 21 L which would be just over 4 1/2 Imperial gallons of glaze. Recipe contains china clay (grolleg?) at 15% so it shouldn't be hard-panning. 5 tablespoons of saturated epsom salts solution added but glaze slurry still leaving heavy drip marks. Typical amount of epsom salts solution would be in the range of 1 tsp per US gallon (0.8 of an Imperial gallon)

Has the efficacy of the epsom salts solution been tested? Have you tried a new saturated solution?

Is the method of dipping the pots part of the issue? Is this a clear glaze high fire? How are the drips with a lower sg? How does the glaze look when fired with a lower sg? 

Thanks Min, I think the issue was Epsom solution not saturated enough. I have made a new Epsom solution and results are promising. Thanks for all your help  much appreciated 

[Gonepotty]

5 hours ago, C.Banks said:

Hi Gonepotty,

I'll go back to lurking - better to remain silent and all that

I appreciate any help :)) thanks for your support 

[Gonepotty]

On 12/15/2023 at 2:49 PM, Hulk said:

"Which do I use ?"

Hard to say.
I'm guessing the larger the container - the larger the mass of glaze - the longer it would spin before stopping, everything else being equal - perhaps due to more mass per unit surface area of the bucket interior, which provides the drag? Easy enough to test; mix thoroughly, pour some off to a smaller bucket, re-test.

My experience is with different glazes and two gallon buckets.
However, I've good results with tweaking the specific gravity and thixotropy of every glaze I've tried.
Two of my glazes I don't add any Epsom salt too at all; they gel great as is.

Added: 21 liters is just over 5.5 gallons, that's a lot of glaze
 

The smaller batch seemed to have better “bounce back “ and seemed uniform with Tony Hansens demonstration.  Yes it’s a huge amount of glaze…think I’ll go smaller next time!