How to Add Bentonite to a Wet Glaze
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What is bentonite?
Bentonite is a very fine particle clay that’s often used as a suspending agent in glazes. Glazes need clay in them to keep all the other materials suspended in the bucket. If your glaze recipe doesn’t have enough clay to stay suspended, it will “hard-pan,” forming a hard, impossible to mix layer on the bottom of the bucket. Bentonite is a very powerful suspending agent and 1-2% is usually enough to keep a glaze suspended.
The Warnings You Get About Bentonite
When I was in school and learning to mix my own glazes, I was warned: “Make sure you add bentonite to the DRY materials and mix them together BEFORE you add any water.”
It was good advice.
The reason for the warning is when bentonite gets wet it swells and gels and sticks together and becomes tricky to incorporate into the rest of the glaze.
If you were to weigh out some bentonite, dump it into a wet glaze and start mixing, the bentonite would clump together. You would have to sieve your glaze a couple of times to try to break those clumps apart so the glaze could be homogenized again.
Nobody wants to do that, right?
But what if you can’t add the bentonite to your dry materials because you’ve already added water to your glaze…? Keep reading, friend.
A New Way to Mix Glazes
When I first learned to mix glazes, we would weigh out all the dry materials into a bucket and then add the water (adding wet to dry).
Whenever I made a glaze that contained bentonite, taking my teacher’s advice, I would add the bentonite as the last dry ingredient and then stir it in with the other dry ingredients before adding the water.
This separates all of the bentonite particles from each other. When the particles are separate, they can’t stick together so they incorporate into the glaze like they’re supposed to.
The downside to this process is it produces a lot of dust in the air, which is a potential respiratory hazard. The dust from glaze materials is harmful to the lungs and avoiding dust clouds is a good studio practice.
Then I heard that some people start mixing their glazes with the water already in the bucket. They add the dry materials directly to the water (adding dry to wet). This reduces the amount of dust in the air by wetting the dry materials right away.
Dry powder being dumped onto more dry powder creates a dusty environment. But dry powder dumped into a bucket of water is exposed to the air for a shorter amount of time. Once it’s wet, it’s no longer a respiratory hazard.
Even if you’re wearing a respirator (which you should be!) anything you can do to reduce the amount of dust released into the air will be better for you and everyone around you.
I happily adopted this new, healthier way of preparing glazes. My health is very important to me. But then what about the bentonite…?
How to Add Bentonite to a Wet Glaze?
(photos and instructions down below)
Now that my procedure had changed (because – safety first!) I could no longer mix the bentonite with the dry materials first to separate the bentonite particles so they couldn’t clump together. I mean, I could but I didn’t want to create unnecessary dust clouds.
Since I was now adding dry to wet, I didn’t know how to get the bentonite into the glaze. I asked around on various ceramic forums to see what other people were doing.
What I found out was, you can add the bentonite directly to plain water! Thank you internet! It’s so simple and convenient, I don’t know why we aren’t taught it from the beginning. At least, I wasn’t.
Some people say they add the bentonite to the water and then high-speed mix it right away. Others let it sit overnight.
I do it a bit differently. I add the bentonite and wait a couple minutes.
As I said earlier, bentonite clumps together if you add it to a wet glaze and try to mix it right away. That’s because when the bentonite particles are partially wet, they attract each other and stick together.
But if you add bentonite to plain water and DON’T TOUCH IT, each of those tiny clay particles will become fully submerged with water on all sides. Once they’re completely wet, the risk of them sticking together is gone and they’ll float freely around the water.
The process is similar to slaking down dry clay, like when you’re reclaiming trimmings. If you add dry trimmings to a lot of water and leave them still, the clay will absorb the water and all the particles will break free from each other, creating a soft layer at the bottom that can be mixed into a smooth slip.
But if you add a little bit of water to a bunch of damp or dry trimmings and then start mixing them around, the clay will stick together and become lumpy.
The key is completely dry clay coming into contact with water and staying still until it can “slake down.” The same is true for bentonite.
Adding Bentonite During the Glaze Mixing Process
So now, when I mix a new batch of glaze that contains bentonite, I calculate how much bentonite is needed first and weigh it out.
I start with water in the bucket and then I add the bentonite to the water. (I usually highlight the bentonite on my recipe page so I don’t forget to add it first).
Then I leave the water undisturbed for a minute or two while I batch out the rest of the glaze recipe (meaning, convert the recipe from % to grams). By the time I’m done, the bentonite is slaked and ready to go.
One way to tell if the bentonite is finished slaking is, it will have all sunk to the bottom of the bucket. There should be no more bentonite floating on top.
And also, as the bentonite slakes down, bubbles will often appear on the surface. If it’s still bubbling, it’s not ready yet. If it has all sunk and stopped bubbling, you’re probably good to go.
You can high speed mix if you want, but my glaze mixing space is very small so I don’t have room for mixing tools on my counter while I’m weighing out dry materials. The mixing comes after all the materials have been added.
Adding Bentonite to a Glaze That’s Already Wet
If I need to add bentonite to a glaze after it’s been mixed (to fix a hard-panning issue, for example) I just weigh out the bentonite (usually 1% of dry glaze weight), sprinkle it into a small amount of water, and wait for it to slake down.
You want enough water to fully cover the bentonite. In this example, I added 50g of bentonite to 200g of water. That’s a 4:1 ratio of water to dry bentonite. I wouldn’t use much less water than that because you want the bentonite to fully submerge. (You don’t need to weigh your water, I’m just like that!)
(I realize the numbers on the scale don’t add up! It was teeter tottering between 249 and 250 and I snapped the photo during a light moment.)
It would have slaked down quicker if I had sprinkled the bentonite more evenly or if the water level was a bit higher. It usually doesn’t take 5 minutes, more like 2-3 mins. I just wanted to make sure for the purpose of the video that it was good to go.
After a couple hours, the bentonite will settle out, leaving a layer of clear water on the top, which I remove with a syringe. I do this because I don’t want to add a lot of extra water to the glaze, I just want to add the bentonite.
The bentonite has settled and the water sitting on top can be syphoned off.
Then I label the container with the amount of dry bentonite in grams and I’m free to add it to any pre-mixed glaze as needed.
Here’s a video of the process:
After adding the wet bentonite to a glaze, it’s important to mix the glaze really well with a high-speed mixer to make sure the bentonite and the glaze become completely homogenized.
One thing I have not tried yet, but may work just fine, is to weigh out the bentonite and add it directly to the water that’s sitting on top of the settled glaze.
Any hard-panned glaze will have a decent layer of water on top. You might be able to just sprinkle the bentonite directly into the glaze and wait for it to slake down. As long as you don’t start mixing right away, I don’t see why it wouldn’t work.
Let me know if you try it!
Have you struggled with adding bentonite to your glazes in the past? Do you have a different method of getting bentonite into your wet glazes? I’d love to hear your thoughts in the comments below.
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Thanks a million for the article on adding Bentonite to wet! Several times I have wanted to add it to a glaze I made, tested and thought after working with it, I wish I had added bentonite. Now I can!
Yay, glad to help!
Sue
Hi sue very helpful the way you explain with your videos as well. What do you do when you store some for future use and you open the container and it has half dried out Thanks
I add just enough water to get it to a fluid state, and then I measure specific gravity to get the water level to where I want it.
How much of the bentonite water combo would u add to a gallon of wet glaze?
Could i do this if i already added Epsom salts/water combo and the glaze now flakes off the pot?
If not, do you have any suggestions on how to save the glazes which are now smooth, but flake off as soon as they are brushed or dipped? Thank you
nice explanation,thx
With existing glazes that have a hard layer at the bottom of the bucket, I take out some of the water and I can gently mix this with the bentonite, just as you describe, and then add it back to the bucket, stir again and then mix it finally.
The previously evaporated water usually does not need to be replenished because the addition of the bentonite makes the enamel structurally more slippery and therefore does not require additional water. If it later turns out that more water can be added to the glaze, we can always add extra.
Hi
I have an ash glaze which has been sitting for several years, and so the bottom of the bucket is hard panned (a new term to me!) i.e. solid at the bottom, just about breaks up with a metal spike.
Can I add bentonite to the water sitting on top (though a kitchen sieve. If so, how does the bentonite mixture break down the solid lump, or is it a question of hard graft breaking up the solid mass?
Many thanks
I would try adding some Epsom salt solution to fix the hard-panned glaze. It will break down the solid lump. I like to pour the water off the top so I can work the Epsom salt solution right into the hard glaze, then pour the water back in after it’s loosened. Then you might want to add bentonite as a backup.
Remembering of course that Epsom Salts only works if there is clay (ball clay/kaolin/raw clay etc) in the glaze recipe. It’s flocculating effect works on the clay particles only…
If a glaze has settled more than I like (or hard panned), I’ll carefully pour off the clear water from the topmost part of the settled glaze bucket. Then add the bentonite (I use the L10 low iron version) to that pour off, and then readd back to original glaze.
Hay una bentonita sódica a la venta en forma comercial, y además, la mayoría de las bentonitas comerciales tuenen un poco de hierro ven su naturaleza.
Cómo afectarán estos 2 componentes (sodio y hierro) a esmaltes de colores delicados y al balance químico de las fórmulas en general?
La misma pregunta, equivale para el agregado de Epsom…
How much clay should typically be in a glaze formula? I have one that isn’t quite turning to cement, but it’s definitely mostly water sitting on top and I have to scrape off the harder materials at the bottom in layers to mix it. It’s an Aventurine Blue Green with chrome and has 7% EPK in it. I was going to add some bentonite to it, so I’m glad I came across this article before just trying to mix it in willy nilly. I want to make sure first though, is the only purpose of bentonite to suspend, or does adding it change the outcome of the glaze at all? I don’t want to change the way the glaze looks.
Hi Julie, With only 7% clay, it makes sense that it would struggle a little bit to stay suspended. It usually takes about 10-15% clay to keep a glaze in suspension, depending what else is in the recipe. I would definitely add 1% bentonite to your glaze and it shouldn’t have any affect on the outcome, only the performance in the bucket.
Great information–thank you. I have a glaze that settles so this time when I mixed it I added .0075 bentonite. (I mixed dry bentonite in with the other dry ingredients and then added all the dry ingredients to water and let it sit before I sieved it.). I could hardly sieve it–it was so thick. This is less than 1% bentonite in the glaze–not sure what to do as it is a glaze I use a lot and this is a very large batch. Not sure if I add more water so that it can be dipped and or poured that it will have the right specific gravity. Please help!!
I have a container of already mixed glaze of which I have used some/quite a lot. Can weigh the wet glaze to calculate the right amount of bentonite uto use?
HI Sue and all of you Ceramicists,
I am very new to all this technical side of clay. I have been a sculptor forever, but never learned the ins and outs of all this. I have never mixed a glaze or even fired a kiln. I got the kiln in the break-up and the glazes as well…I am thrilled to have found your simple information. I am excited to learn more of the technical side of glazing and firing. I will look here first!! And, oh boy, I’ll even be making my own glazes one day. How fun!
Continue sendo essa pessoa maravilhosa que você é!
Só dá quem tem para dar.
Parabéns!!!!
Penso como você e compartilho sempre o pouco que sei.
“Quando à beira da morte, Alexandre convocou os seus generais e relatou seus 3 últimos desejos: 1 – que seu caixão fosse transportado pelas mãos dos médicos da época; 2 – que fosse espalhado no caminho até seu túmulo os seus tesouros conquistados (prata, ouro, pedras preciosas…); e 3 – que suas duas mãos fossem deixadas balançando no ar, fora do caixão, à vista de todos. Um dos seus generais, admirado com esses desejos insólitos, perguntou a Alexandre quais as razões. Alexandre explicou: 1 – Quero que os mais eminentes médicos carreguem meu caixão para mostrar que eles não têm poder de cura perante a morte; 2 – Quero que o chão seja coberto pelos meus tesouros para que as pessoas possam ver que os bens materiais aqui conquistados, aqui permanecem; 3 – Quero que minhas mãos balancem ao vento para que as pessoas possam ver que de mãos vazias viemos e de mãos vazias partimos.”
Thank you Marize!!
Hello Sue, this is helpful information. I have a 5 gallon bucket of a commercial glaze that is hard pan. I have talked with the company twice and am told to find the specific gravity. My husband has used a crow bar to pry it off the bottom and the. We can use a heavy duty drill to mix it. I’ve added the epson salt water within 5-10 minutes it hard pans again. I have lost some of the glaze due to spillage when using the drill. The company has stated several times they have a product I could buy ‘suspend aid’ to help with this. But I’m thinking of trying your option of using some of the water off the top of the bucket to mix with bentonite. I don’t know what percentage of Clay is in the glaze. Would I still use 1%? Or more? What are your thoughts of this idea?
I think it’s a great idea to add some bentonite to this glaze. Adding bentonite will also help the Epsom salts to be more effective. What size is your glaze bucket? I would start with adding 1% of the estimated dry weight of the glaze in the bucket. It’s ok if it’s not exactly 1%.
Sue, porque não fazer uma solução de bentonita?
Tenho essa dificuldade no glaze e qualquer hora vou comentar com o Derek.
A quantidade de bentonita fica fixa nos adendos e eu não concordo.
Um esmalte puro está levando 2% de bentonita em 100g. Acontece que ao colocar 4% de ultrox e 6% de cor eu tenho 110% de esmalte e não 100%. A água fica proporcional, mas a bentonita não. Fica fixa.
Uma solução de bentonita resolveria.
Eu teria que calcular primeiro a concentração.
Se coloco 80g de agua e 40g de CMC preparado em cima do total eu teria que ter dentro desses 80g as 2 gramas de bentonita pretendidas, ou seja: uma concentração/solução com 25g de bentonita em 1l de água.
Agora sim. Ao colocar 80% de solução em uma base 100% eu estaria entrando com 2g e ao colocar 80% em um esmalte com 110% eu estaria colocando 2.2g.