Sodium Silicate Pottery Cracked Surfaces: Slab Building Technique

Creating textured slab from sodium silicate on black clay

How do potters achieve those amazing crackled patterns in their ceramic pieces? With the magic of Sodium Silicate. You may have seen artists use this clear, liquid medium on the outside of wheel-thrown pottery before stretching the work into larger forms with various cracked designs running across the surface.

What exactly is Sodium Silicate? And how does it work?
Sodium silicate (or water glass) truly is a “magic” liquid that can be used for a number of clay altering properties. It’s a sticky, thick consistency that is made by dissolving silica gel in sodium hydroxide. Sodium silicate is a popular choice as a deflocculant (a chemical added to slips and glaze to increase fluidity / help them flow better), usually in combination with soda ash to avoid the slip becoming stringy. It’s cheap, reliable and effective but should be used sparingly. It’s also a little harsher on plaster moulds than more modern deflocculants, such as Darvan 7.
It can be used as a glue to bind ceramic greenware together, and is stronger than regular slip/slurry due to its forced interlocking molecular bond on the reattached pieces. Once fired, it forms a ceramic bond – this is commonly called magic water in the following quantities:
1 litre water
2 teaspoons sodium silicate
1/4 teaspoon soda ash

It can even be incorporated into bodies to improve their dry strength and last but not least, used to create big, beautiful cracked patterns on clay surfaces.

I don’t own a throwing wheel so how can I use sodium silicate on my slab built pieces?
Luckily, it’s not necessary to own a fancy, expensive wheel to start incorporating this medium into you work and creating similar crackle patterns. I’ve made a simple, easy to follow video that will show you exactly how to start using sodium silicate in your hand-building projects:

Is Sodium Silicate a hazardous material?
Personally, I have had no negative side effects handling sodium silicate (I do avoid touching it in it’s wet liquid form) and it wouldn’t hurt to wear a pair of gloves if you’re worried about an allergic reaction. I’ve heard through the ceramics community grapevine of individuals experiencing chemical burns, but the same goes for those dying their hair with peroxide for example – some people may be more sensitive than others.
Here is some further technical info sourced from Oxy.com: “Sodium silicates are non-flammable, non-explosive, and non-toxic. They are, however, alkaline materials and pose hazards to the skin and eyes. The physiological effects of contact vary with the alkalinity of the silicate involved, and range from causing irritation to causing chemical burns”.

I encourage you to give sodium silicate a go in your next textured project. A little goes a long way to create some epic, organic-looking effects. Perfect for mimicking nature such as tree bark, drought wastelands or a dried-up seabed. Perhaps you need to create peeling skin, animal leather, crackled faces, a burned-up zombie, or just a new way to incorporate patterns and mix colours… the possibilities are endless!

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