Understanding the lesser-known terms, materials, and processes in the world of pottery can be fairly exciting, and one such material is “Grog.” Also popular as chamotte and firesand, this raw material is an ideal choice for ceramic pottery. With a fairly high composition of alumina and silica, grog brings in some of the best features for enthusiastic potters.
How is the grog prepared?
Grog is generally produced through the process of firing specific fire clays at high temperatures & screening the same to specific particle sizes. Now, there is another method that comes into play. This method requires the Grog to be produced from pitchers. In this case, the particle size distribution is a bit coarser compared to any other material used for preparing clay bodies.
Grog is mostly porous & packs in low-density particles.
What are the properties of Grog?
Grog is packed with a minimum of 40 percent alumina, 30 percent silica, 4 percent iron (III) oxide, magnesium oxide, and 2 percent calcium oxide. Given the presence of all these materials in its composition, the melting point of this ceramic maker is approximately 1780oC. However, its boiling point goes higher than 9000oC.
Apart from this, Grog’s maximum water absorption capacity stands at 7 percent, with the coefficient of thermal expansion standing at 5.2 mm/m. The material’s thermal conductivity is about 0.8 W/ (m-K) when kept at 100oC & 1.0 W/(m-K) when kept at 1000oC. Plus, it isn’t easily wetted when mixed with melted steel.
Here is a quick table to help you understand the chemical composition of grog.
Grog Components | Percentage of Raw Material |
| SiO2 | 18.02 |
| MgO | 6.80 |
| Al2O3 | 66.00 |
| CaO | 0.90 |
| Na2O | 0.60 |
| Fe2O3 | 2.03 |
| LI | 2.55 |
| TiO2 | 2.60 |
| K2O | 0.25 |
What are the applications of Grog?
Grog is primarily used in sculpture and pottery artwork to include a gritty and rustic texture termed “Tooth.” The material is known to bring down the shrinkage & fasten the drying process.
Further, the features present in Grog help prevent any kind of defect such as lamination, crow feet pattern, or cracking. The coarse Grog particles are integrated in a way that helps open up the green-colored clay body & helps the gases escape easily.
Grogs also add to the structural strength of thrown and hand-built pottery when shaping. However, it might diminish the fired strength. A finer particle would suggest that the bond between the clay elements would be closer. This would ultimately create a dense & strong-fired product.
When dried up, the grog strength increases and is similar to passing the material through a 100-mesh sieve. However, this decreases when the material passes through a 200-mesh sieve. In South and Middle Europe, this material is used for the creation of fire-resistant chamotte bricks & mortar to help construct fireplaces, industrial furnaces, and old-style furnaces.
Further, it is also used as a component for adhesives and sealants that are used for high-temperature applications. A good example of Grog being used in real life is a pizza stone that is made from the chamotte. Given the fact that this stone can easily absorb heat, one can easily bake bread or pizza on this stone when kept in any regular oven.
With grog, the advantage is an evenly distributed heat pattern. A domestic or commercial oven tends to cool down after you open the door. However, any stone made of grog tends to remain hot while ensuring an evenly distributed bake.
Another advantage of this material is that this stone tends to absorb a good amount of moisture, giving you a drier baking experience. In case you wish to experiment with grog and need a quick starter kit for your DIY adventures, you can try the Crockd DIY Pottery Kit. The kit is designed for easy sculpting for beginners and has multiple tools as per your requirements.
Does grog reduce the cracking of a pottery piece?
Grogged clay brings in low plasticity. Any type of clay’s plasticity can be majorly influenced due to the particle size of the clay, aging, or water content. You could benefit from clay that has low plasticity during the pottery drying process.
This is because grog brings in superior drying features given its improved permeability & water channeling without any obstruction.
Is glazing affected by grogged clay?
As opposed to normal clay, grogged clay tends to affect the final output post-glazing. This is because grogged clay can react with all the chemicals present within the glaze. Further, grogged clay can be perfect for firing purposes. This is because grog is ideal for expanding & contracting without any possible cracking.
Grog has the benefit of adding an amazing and shiny texture to the ceramic and pottery pieces. Also, you need to keep in mind the overall temperature at which the grogged clay is being fired. This is because this particular clay can be fired way quicker as opposed to normal clay.
Soft vs. Hard Grog
Now, very few potters are aware of the fact that there is soft and hard grog. The best way to distinguish the two is to determine the firing temperature. In general, if a pottery item needs to be fired at a higher temperature, needing a Cone 10 or above, it is termed hard.
On the other hand, a material that fires up below Cone 10 temperature can be termed a soft grog. The latter is generally made use of due to its porosity & reduced stickiness within the clay body. However, if you happen to fire a soft grog beyond Cone 10, it can melt down.
With hard grog, the ultimate resultant is way more robust. This is because it is completely mature. Also, it won’t melt down as the piece has been completely fired.
Conclusion
Keep in mind that the addition of grog to the clay helps reduce any shrinkage or cracking. Not just that, grog will help make your clay easy to work with while helping it hold in shape. So, get the best texture with grog added to the pottery work and flaunty your creations.
