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Hi, 

I’m firing earthenware at 1050 C using a commercial Ferro glaze. 

I can’t seem to find a fix for this nasty drip marks when dipping.. In this particular case the specific gravity was 1.5, too high, recommended is 1.4. but even at 1.4 i’m getting drip marks.

My guess is the glaze is under flocculated, can someone correct me if i’m wrong? epsom salts probably don’t help, tried on a small batch, i guess theres little to no clay.

i’ve made it thixotropix by adding an additive similar to OPTAPIX G1308 (binder and flow agent). that made it a little better but not good enough.

I’d love to hear your thoughts on how to go about this issue.

 

https://imgur.com/gallery/odrmHGD

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Those nasty drip marks look like a slip texture on the cup...but if they are that persistent, I'd look for a different glaze to work with. I'm not a dipper, so I've never experienced this before. Have you fired any of the pieces yet? If not, give it a shot and see what you come out with. You might like the effect. If you have, what does it look like?

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Tony Hansen's suggestions https://digitalfire.com/4sight/library/thixotropy_and_how_to_gel_a_ceramic_glaze_73.html have been very helpful for me.

I use Epsom salts (or vinegar).

Have found that a good grip is also helpful, for it allows me to give the piece a downward shake and twist+flip to fling away gathering drips; from there I'll run any remaining drip around and around the rim ...once the glaze is set up, I'll wet a finger and smooth the drip (if any). Timing is important; practice helps. Be sure to stir before each application - that thin layer of more watery glaze at the surface will wreak havoc.

Good luck!

Edited by Hulk
two goods
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The specific gravity won’t affect how the glaze drips but the rheology, or how the glaze flows will. This is the thixotropy of a glaze, or lack thereof. While I am a fan of Tony Hanson, Sue Macleod is a much more thorough and effective teacher on this subject. Her explanations are far more approachable. She goes into more depth on how to troubleshoot and fix things. 
https://suemcleodceramics.com

Epsom salts would have been my first choice to fix a dripping issue. How much did you add, and was it thoroughly incorporated? Did you add your Epsom salts as dry material, or did you add them as a small amount of a super saturated solution?

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First, do the drips show after firing? With many glazes it's a non-issue, especially if you're layering and letting it run anyway. It looks to me like the glaze is simply too thick. Thin it out a little, then increase the dip time to compensate. In my studio, I mix the glaze so they're like a creamy chocolate milk consistency, then dip for 6 seconds. My glazes are a bit more watery than a lot of other studios that my students have worked in, but it gives them more control over the thickness of the application.

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For forms like those in the linked image I would pour the inside then hold the pot by the foot ring and dip the outside. Hold it upside down and slowly rotate the pot. Let any surplus glaze roll around the rim edge to avoid a drip when you turn it right side up. Touch up any spots where your fingers held the pot with a brush.

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2 hours ago, Callie Beller Diesel said:

The specific gravity won’t affect how the glaze drips but the rheology, or how the glaze flows will. This is the thixotropy of a glaze, or lack thereof. While I am a fan of Tony Hanson, Sue Macleod is a much more thorough and effective teacher on this subject. Her explanations are far more approachable. She goes into more depth on how to troubleshoot and fix things. 
https://suemcleodceramics.com

Epsom salts would have been my first choice to fix a dripping issue. How much did you add, and was it thoroughly incorporated? Did you add your Epsom salts as dry material, or did you add them as a small amount of a super saturated solution?

I made a super saturated solution and kept adding to a small batch. I didn’t notice a difference, i was looking for thixotropy, mainly how it swirls backwards after you mix it. 

epsom salts from my understanding change the charge of the clay particles in the glaze, i assume this glaze has little to no clay. Wasn’t able to find a full composition of this glaze on Ferro’s website.

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1 hour ago, neilestrick said:

First, do the drips show after firing? With many glazes it's a non-issue, especially if you're layering and letting it run anyway. It looks to me like the glaze is simply too thick. Thin it out a little, then increase the dip time to compensate. In my studio, I mix the glaze so they're like a creamy chocolate milk consistency, then dip for 6 seconds. My glazes are a bit more watery than a lot of other studios that my students have worked in, but it gives them more control over the thickness of the application.

So i thinned it out to 1.4 SG, much thinner now, similar composition like you’re describing. I’ve increased the additive by 0.15%, i can feel it’s more thixotropic now, meaning that it bounces back more when you mix it.

I’ll have to check tomorrow to see how much it settled, i assume it won’t settle too much.

Here’s the test dips, 5 second dip.

Not perfect.. the final result will look good for this matte clear glaze.

eventually i want to add some color, smallest unevenness will show as a darker color and looks bad in my opinion. Trying to get the most even drip :)

DehrmWU.jpg

1rO1me7.jpg

 

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2 hours ago, Callie Beller Diesel said:

The specific gravity won’t affect how the glaze drips but the rheology, or how the glaze flows will. This is the thixotropy of a glaze, or lack thereof. While I am a fan of Tony Hanson, Sue Macleod is a much more thorough and effective teacher on this subject. Her explanations are far more approachable. She goes into more depth on how to troubleshoot and fix things. 
https://suemcleodceramics.com

Epsom salts would have been my first choice to fix a dripping issue. How much did you add, and was it thoroughly incorporated? Did you add your Epsom salts as dry material, or did you add them as a small amount of a super saturated solution?

thixotropy is the issue indeed.. increased it a little and that extends the drying time and allows it to flow more.

for really large pieces the flow time was too little, and quickly built up in some areas.

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@Mitzuuu89 I used to use a lot of true celadons years ago, and learning about thixotropy was a game changer for sure. With Epsom salt solution or any other additive, you have to add just a little at a time and mix for a minute or two before it becomes noticeable. If you overshoot it goes horribly wrong. 

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11 hours ago, Mitzuuu89 said:

, i assume this glaze has little to no clay. Wasn’t able to find a full composition of this glaze on Ferro’s website.

FYI- The general goal is 10% to let’s say 20% clay to help with maintaining suspension.

Edited by Bill Kielb
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