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Sodium Silicate

Alternate Names: Waterglass

Description: Na2SiO3 Deflocculant, De-flocculant

Oxide Analysis Formula
Na2O 50.78% 1.00
SiO2 49.22% 1.00
Oxide Weight 122.10
Formula Weight 122.10


Sodium silicate (SS) is a sticky, viscous liquid. It is produced by dissolving silica gel in sodium hydroxide (there a many videos on Youtube on how to do this).

Sodium silicate is the most popular deflocculant used in casting slips for many years (as a source of sodium ions). It is nearly always used with soda ash (when employed alone it can make a slip 'stringy' and thixotropic). The material is effective, reliable and inexpensive. However, it attacks the plaster in molds much more than more modern deflocculants and it is easier to over-deflocculate a slip with sodium silicate.

There are potassium-based deflocculants that are similar to the corresponding sodium ones. They can be employed where the presence of sodium is undesirable. Soda ash is more suitable for deflocculating glazes. In addition, a wide range of organic deflocculants is available as alkali salts of pyrogallic, humic or tannic acids. They have long working ranges and can increase the apparent plasticity of the clay. As noted, their use prolongs mold life compared with sodium silicate and soda ash and they are less prone to over-deflocculation. Tetramethylammonium hydroxide is also an organic compound that is used where residues from inorganic salts cannot be tolerated. It is a strong base that can even attack glass and quartz.

Because sodium silicate is sticky and dries hard, it can be used as a glue to bind ceramic particles together, even aggregates. On firing, it forms a ceramic bond. Mixtures of sodium silicate and perlite, for example, can be rammed into molds to form shapes that dry with zero shrinkage and have excellent insulating properties. It can be incorporated into bodies to improve their dry strength. As the main ingredient in Magic Water, it can bind leather-hard clay sections better than the clay slurry (slip) alone.

Related Information

The high porosity of this clay enables sealing against water leakage

Tap picture for full size
Silicone sealer on pottery planters

This body has high porosity, almost 25%. It is L4410P, a dolomite-based low-fire whiteware, Plainsman Clays makes this as a product named "Snow". But this high porosity has some advantages, one of them is that it soaks up silicone sealer well. The slip-cast piece on the left was sealed (you can see the surface sheen) and it is impermeable to water penetration (the glaze is not crazed so water cannot penetrate there either). The piece on the right soaks up water readily (on the lower unglazed portion). Sealing this specific body is doubly important because the dolomite particles within can rehydrate over time, especially in damp climates, causing pieces to crack. Even the foot rings of functional pieces should be sealed, not just to prevent hydration but also waterlogging.


Articles Understanding the Deflocculation Process in Slip Casting
Understanding the magic of deflocculation and how to measure specific gravity and viscosity, and how to interpret the results of these tests to adjust the slip, these are the key to controlling a casting process.
Articles Understanding the Terra Cotta Slip Casting Recipes In North America
This article helps you understand a good recipe for a red casting body so that you will have control and adjustability.
Articles Binders for Ceramic Bodies
An overview of the major types of organic and inorganic binders used in various different ceramic industries.
Typecodes Additives for Ceramic Glazes
Materials that are added to glazes to impart physical working properties and usually burn away during firing. In industry all glazes, inks and engobes have additives, they are considered essential to control of cohesion, adhesion, suspension, dry hardness, surface leveling, rheology, speed-of-drying, etc. Among potters, it is common for glazes to have zero additives.
Typecodes Generic Material
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes Electrolyte
Materials used to control slurry properties of glazes and slips (vicosity, specific gravity).
Typecodes Additives for Ceramic Bodies
Materials that are added to bodies to impart physical working properties and usually burn away during firing. Binders enable bodies with very low or zero clay content to have plasticity and dry hardness, they can give powders flow properties during pressing and impart rheological properties to clay slurries. Among potters however, it is common for bodies to have zero additives.
Materials Sodium Carbonate
Materials Perlite
Materials Darvan
A common deflocculant used to disperse ceramic suspensions to minimize their water content, a more modern material than sodium silicate.
Materials Acumer Dispersant Polymer
Sodium silicate on wikipedia
Hazards Sodium Silicate Powder Toxicology


Frit Softening Point 1080C M
Density (Specific Gravity) 2.40
By Tony Hansen
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