Sodium silicate turned my glaze into thick sludge
Can you save a glaze that has turned to pudding after adding too much sodium silicate?
Question: I added way too much sodium silicate to two big buckets of glaze. They were too thick and water wasn’t helping so I decided to deflocculate with sodium silicate. They have turned into a thick sludge. Can I save these buckets?
Yikes.
In my experience, too much sodium silicate will ruin a glaze and there’s little to no chance for recovery. I did this on purpose because I was experimenting, so I didn’t ruin a glaze by accident. I ruined a glaze on purpose.
Here’s what can happen when you add even a little bit too much sodium silicate.
I was testing the effects of different flocculants or deflocculants. Sodium silicate is a deflocculant, also known as a dispersant, which reduces the viscosity of your glaze without adding extra water.
Why do we need to deflocculate?
Sometimes we have glazes that are very, very thick. Say we brought our specific gravity down to 1.5 by adding water but the glaze is still very thick in the bucket.
If we keep adding more and more water, that can lead to issues with crawling because more water equals more shrinkage during the glaze drying process. Most glazes have a percentage of clay in them to keep them suspended in the bucket. Clay shrinks when it dries and therefore, our glazes shrink when they dry. The more clay you have in your glaze, the more your glaze is going to shrink while it dries on your pots. And the more water you have in your glaze, the more the glaze will shrink.
Think about clay bodies, for example. If you have a liquid slip that you use for attaching, that slip shrinks way more than clay that’s already leatherhard. Leatherhard clay shrinks less because it has already shrunk from when it was more wet. The shrinkage happens because the water evaporates and the particles move closer together.
If you keep adding water to a glaze that’s not thinning down, that’s usually because it’s in a flocculated state. So for the person asking the question, it was a good idea to deflocculate this glaze. But sodium silicate is one of those deflocculants where you can easily overdo it, even if you add just a little bit too much.
How to deflocculate?
When you deflocculate a glaze, you should add a little bit of your deflocculant, high speed mix and then the viscosity of the glaze should go down. Your glaze should visibly thin down in the bucket. If it doesn’t you can add a little bit more.
So when you start, the glaze is thick and moving very slowly as you’re mixing. Then you deflocculate and all of a sudden, it starts moving really nicely, fluidly, and more like water.
A caution about over-deflocculating
When you over-deflocculate your glaze, first it reaches a point of “absolute deflocculation” (or something, I just made that up). It becomes completely deflocculated. And if you add more deflocculant, then it becomes over-deflocculated and the reverse happens. It thickens up again.
It turns into a sludge and there’s no going back.
So I did try this way back before I knew anything about it. There’s a video in my Facebook group of me, in awe, because I’d never experienced this before. I’m like, what is happening here? Why is my glaze so thick? And then I learned about over-deflocculating.
In my experiments, I learned that with sodium silicate, you have to actually add a very small amount at a time, high speed mix, let it sit for a bit. You have to allow it to take effect before you add any more, because once it thickens up, there’s no going back.
I tried everything. I tried adding a bunch of water, mixing it up and then pouring the water off the top to see if that could remove some of the deflocculant and fix the glaze, and it wasn’t able to be fixed. Luckily for me, it was just a test and I just got rid of it.
Which deflocculants to use
WARNING, I don’t recommend sodium silicate as a deflocculant. If you can, get something else like Darvan 7 (chemical name is sodium polymethacrylate). There are other products around the world (I live in North America). Dispex and Dolapix are two other deflocculants. They all start with ‘D’ which makes it easy to remember they all work the same. Sodium is the active deflocculating ingredient, and they are more ideal than using sodium silicate as a deflocculant. They are more user friendly and have a much wider window for how much you can add without ruining your glaze.
I’m sorry if you’ve added too much sodium silicate to your glaze. Hopefully it’s a good learning experience and you won’t do it again.
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