Clay enthusiasts, unite!
Welcome back to the Ceramic Materials Workshop blog, fellow clay enthusiasts! Today, we’re diving deep into the fascinating world of clay body absorption.
What is Clay Body Absorption?
Clay body absorption is a fundamental property of ceramic materials that dictates how much water a fired clay body can absorb. It’s a crucial factor influencing the durability, functionality, and overall performance of your ceramic creations. Â
Want to test your commercial clay body profile testing FOR FREE? (Click here!)
Why Does Absorption Matter?
Simply put, absorption dictates how your clay body interacts with water and other substances, significantly impacting the long-term performance and safety of your ceramic pieces. A high absorption rate can lead to a host of problems:
- Cracking: Water absorbed into the clay body can expand during freeze-thaw cycles, exerting pressure and causing cracks. This is especially problematic in colder climates.
- Staining: Porous clay bodies readily absorb liquids, leading to unsightly stains from coffee, tea, or other substances. This can diminish the aesthetic appeal and even affect the hygiene of the piece.
- Bacterial Growth: The porous nature of high-absorption clay creates an ideal environment for bacteria to thrive. This is a major concern for functional ware, as it can pose a health risk.
- Weakened Structure: Over time, repeated absorption and drying cycles can weaken the clay body, making it more prone to chipping, cracking, and eventual failure.
- Glaze Issues: High absorption can interfere with glaze adhesion, leading to crazing (cracks in the glaze), shivering (glaze flaking off), or uneven glaze application.
Rose puts it perfectly: “Just like I wonder about Matt every day, you may wonder about your clay body.” Understanding absorption is key to creating durable and functional ceramics.
The Vitrification Connection
Vitrification is the transformative process that occurs during firing, where the clay particles begin to fuse and form a glassy phase within the clay body. A well-vitrified clay body is like a superhero – tough, durable, and resistant to all sorts of challenges. It’s less porous, stronger, and more impervious to water.
Absorption is intimately linked to vitrification. As the clay body vitrifies, its absorption rate decreases. Therefore, measuring absorption is a good indicator of the degree of vitrification.
The Magic Number: 0.5%
We firmly believe that a clay body must have less than 0.5% absorption to be considered truly vitrified and suitable for functional use, especially for tableware.
This stringent standard is based on guidelines from organizations like the American Society for Testing and Materials (ASTM) and ensures your pieces are not only beautiful but also functional, durable, and safe for use.
This low absorption rate signifies a high degree of vitrification, minimizing the risks associated with water absorption.
Testing, Testing, 1, 2, 3!
Testing your clay’s absorption rate is a straightforward, albeit detail-oriented, process. (Read more about how to make a plaster slab for testing clay bodies)
Here’s a simplified version:
- Prepare: Create several test tiles of your clay body.
- Fire: Fire the tiles to your desired firing temperature and hold time.
- Dry Weight: Thoroughly dry the fired tiles in a kiln or oven and weigh them accurately. This is your “dry weight.”
- Boil: Immerse the tiles in boiling distilled water for a specified period (typically 2 hours).
- Soak: Allow the tiles to soak in the cooling water for 24 hours.
- Saturated Weight: Remove the tiles, pat them dry with a towel, and weigh them immediately. This is your “saturated weight.”
- Calculate: Use the following formula to calculate the absorption percentage: ((Saturated Weight – Dry Weight) / Dry Weight) * 100
Want to test your commercial clay body profile testing FOR FREE? (Click here!)
Busting the Myths
Unfortunately, there are many misconceptions surrounding clay body absorption testing. Some suggest that tap water or shorter boiling times are sufficient. These shortcuts can lead to inaccurate results. Using distilled water and adhering to standardized testing procedures are crucial for reliable data. Don’t rely on guesswork – proper testing is essential.
The Underfired Dilemma
Many clay bodies on the market are marketed as functional despite having absorption rates significantly higher than 0.5%. We believe these clays are often underfired. While they might appear functional initially, they are likely to be more fragile, prone to staining, and potentially harbor bacteria.
As Rose wisely says, “The reality is, it is a big deal. Clay needs to be vitrified in a modern context to be functional.” Don’t compromise on quality and safety – test your clay and demand better from suppliers.
Join the Movement!
We encourage you to test your clay bodies and demand better from manufacturers. Together, we can raise the bar for ceramic quality and ensure our creations are functional, durable, and safe.
Want to test your commercial clay body profile testing FOR FREE? (Click here!)
Still Curious? Watch our YouTube!
Self-Absorbed | How to find your clay body’s absorption – Watch as Rose guides you through the entire process, from preparing your clay samples to calculating the absorption rate. You’ll learn how to ensure that your clay is properly vitrified, making it durable, non-absorbent, and ready for functional use.
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Ready to dive deeper?
Loved learning about ceramic glazes? Want to go even deeper? Check out our Workshops & Courses, now available in Spanish, or YouTube Channel where Matt breaks it all down, myth-busting and Stull chart included!
