Could the ordinary clay found around Lesotho’s Roma Valley become the key to producing beautiful ceramic tiles, bricks, and pottery—right here at home? Lebohang Pule, a student at the National University of Lesotho (NUL), decided to find out.

It all started with a simple thought: why is Lesotho still importing most of its ceramic products, when clay—the very stuff that makes ceramics—lies everywhere underfoot in the country? Of course not all clay can make tiles, that’s why it’s important to know which can.

“We’ve been sitting on this resource for years, Its everywhere,” Lebohang said, “but nobody really knew for sure if the ones we have around the Roma Valley was good enough for making quality tiles or ceramics. I wanted to test that and see what this clay could actually do.”

So off she went, under Mr Innocent Hapazari’s guidance, collecting clay from two places not far from the NUL campus—Mangopeng and Halebamang. Mangopeng is a quiet area just 5 km away from NUL, while Halebamang is a residential area near a site where bricks have been made in the past. Lebohang carefully gathered soil samples from both spots, making sure to get enough material to run a full set of tests back in the lab.

Once back to the lab, the real detective work began. First, Lebohang air-dried all the samples to remove natural moisture, then oven-dried them at 105°C to make sure the results wouldn’t be affected by any remaining water. After drying, she ground the clay into fine powder using a mortar and pestle—just like traditional ceramicists would prepare raw clay, but with a scientific twist.

Then came a series of tests to unlock the clay’s secrets.

1. Particle Size Analysis (Sieve and Hydrometer Tests)

Lebohang needed to know how fine or coarse the clay was. Why? Because the size of clay particles affects everything from workability to strength to how the clay shrinks or cracks when fired. Using a stack of sieves, she shook the dry clay to see what sizes remained on each level. The rest—the really fine stuff—was tested with a hydrometer to check the proportions of silt and clay particles floating in water.

The results told her that the grey clay was well-graded, with a wide variety of particle sizes, which is great for compaction and producing strong, less porous ceramics. The red clay, however, was more uniform in particle size—potentially easier to shape but slightly weaker unless mixed with other materials.

2. Swelling Test (Free Swell Method)

Clay’s tendency to swell when wet can cause problems in ceramic production—like cracking during drying or firing. Lebohang tested this by putting equal amounts of dry clay in two cylinders: one filled with water and the other with kerosene. After 24 hours, she compared how much the clay had expanded in each liquid. The grey clay swelled a lot—suggesting the presence of montmorillonite, a mineral known for absorbing water. The red clay hardly swelled at all—likely due to kaolinite, which is more stable and less expansive.

3. Chemical Testing (pH, Organic Matter, Cation Exchange Capacity)

To understand how the clay would behave during shaping and firing, Lebohang also measured pH, organic matter, and CEC. The pH tells if the clay is acidic or basic—affecting plasticity and color during firing. Grey clay was slightly acidic (pH 6.09), while the red clay was more neutral (pH 7.28)—ideal for ceramics.

She also used the Loss-on-Ignition method to measure organic matter, heating the clay to 375°C until all organic material burned off. The result: both clays had low enough organic content (below 6%) to avoid defects like black core formation during firing.

Next, she tested the CEC (Cation Exchange Capacity)—important because clays with high CEC hold water and ions differently and this affects workability and strength. Grey clay had slightly higher CEC, consistent with its montmorillonite content, while red clay’s lower CEC matched its kaolinitic nature.

4. Firing Tests (Shrinkage and Water Absorption)

Finally came the ultimate test: could these clays survive the heat and become proper ceramic materials? Lebohang shaped little test briquettes from both types of clay, let them dry slowly (to prevent cracking), and fired them in an oven at three temperatures—800°C, 900°C, and 1000°C.

After firing, she checked how much the clay shrank (important for making pieces that stay the right size) and how much water they absorbed (affecting strength and durability). The grey clay shrank more—expected, given its possible montmorillonite content—but stayed within industrial standards. The red clay barely shrank but also performed well.

Water absorption decreased as firing temperatures increased, thanks to the formation of glassy phases that sealed the pores. Both clays absorbed between 11% and 13% water—again, within acceptable limits for making floor tiles and bricks.

So what does it all mean?

“The grey clay has potential for stoneware tiles, bricks, and heavy-duty floor tiles because it can handle firing well and forms strong, dense ceramics,” Lebohang said. “The red clay could be ideal for making floor tiles—it’s stable, predictable, and easy to work with.”

In fact, both types of clay meet international ceramic production standards—a big deal in a country where nearly all ceramic tiles and bricks are imported.

“If we start using our own clay to make tiles and bricks,” she said, “we can save money, create local jobs, and even start exporting someday. The potential is huge—and right under our feet.”