Materials Monday: What is Grog and Why Should I Use It?
- , by Haley Stanaford
- 2 min reading time
Grog is in many commercial and homemade clay bodies, but what is it? You may have heard this mentioned around a studio but maybe not explained too thoroughly.
Grog is fired ceramic that has been ground up into smaller, rock-like, particles. So why is it in your clay? Well, grog helps with some different things. It lowers shrinking in the clay body, reduce cracks from drying, improves structural integrity allowing you to build bigger, and make it more resistant to thermal shock (especially helpful in raku clay bodies).
Grog can come in different sizes called meshes. The higher the number mesh, for example 30 mesh grog, the finer it is. 10 mesh grog is a very large grain, comparatively.
Grogs are typically grayish in color, however there is a type of grog called Molochite which is the porcelain version of a grog that is white in color.
So, grog sounds pretty cool, huh? So why isn’t it in every clay body if it helps so much? Well, firstly grog does have a look with it. You will typically be able to tell when a piece has grog in the clay body just by looking at it as it will have, sometimes raised, little dots of rock spread through it. Which is different than speckled clay bodies as those are created through an addition of a material called manganese dioxide. While not all grogs are visually very apparent, the larger grains are typically.
Photo from digitalfire’s page about grog
Another reason for grog not to be in every clay body is because larger grains do not do well in throwing. Imagine if you threw with a clay body that had some little rocks in it. The rocks will interact with your hands in maybe a not so pleasant way. This does not mean a groggy clay body cannot be thrown with as I have done so and got the job done, it just isn’t always the best. Grog will also take away some of the clay’s plasticity, especially when used in large quantities.
Now that’s a lot of negatives about grog but it is amazing in sculptural and handbuilding clay bodies. Its properties greatly help building and allow the maker to do more with the clay.
Grog is an additive in clay, meaning it can be added to any clay body without messing with the chemistry of it. For general handbuilding 5-10% grog does wonders. For a hearty sculptural clay body that can make larger sized work, 15-20% will go a long way.
If you want to learn more about grog, mullite, mulcoa, and more additives in clay, read the article written by Cindy Bracker here.
Haley Stanaford is currently a Post Baccalaureate student in ceramics at the University of Kansas where she is currently taking a Clay and Glaze Formulation taught by Colby Charpentier in addition to her studio practice. She also is a Sales Representative at Bracker’s Good Earth Clays in Lawrence, Kansas.
