Finding Clay

Part of Pottery and Ceramics

Locating and identifying pottery-grade clay deposits in your environment.

Why This Matters

Clay is one of the most common minerals on Earth — it forms wherever rocks weather in the presence of water, which is nearly everywhere. Yet finding clay that’s actually suitable for pottery is a different matter. Deposits vary enormously in purity, plasticity, mineral content, and firing behavior. The difference between a handful of muddy silt and a seam of excellent pottery clay can mean the difference between vessels that last years and ones that crumble on first use.

In a rebuilding scenario, finding a reliable clay source is a strategic priority. Pottery provides water storage, cooking vessels, food preservation containers, building materials, and eventually the crucibles that enable metalworking. A community settled near good clay has a permanent, renewable resource — clay deposits are geologically vast, and a single exposed seam can supply a potter for decades.

The good news is that usable clay exists in almost every landscape. The techniques in this article will help you find it efficiently, evaluate deposits quickly in the field, and understand which geological settings produce the best pottery clay.

How Clay Forms

Understanding clay’s geological origin helps you predict where to find it.

Primary (Residual) Clay

Clay that remains where it formed — at the site of the parent rock’s decomposition:

• Found on or near weathered granite, feldspar-rich rock, or volcanic deposits
• Often white or cream-colored (kaolin)
• Tends to be coarse-grained and less plastic
• May contain unweathered rock fragments
• Best for: High-temperature applications, refractory work, white-bodied pottery

Secondary (Sedimentary) Clay

Clay that has been transported by water, wind, or ice and deposited elsewhere:

• Found in river valleys, flood plains, lake beds, ocean margins
• Typically more fine-grained (the transport process sorts by particle size)
• More plastic (easier to work) than primary clays
• Often colored by iron and organic matter (red, brown, gray)
• May contain fine sand, silt, and organic material
• Best for: General pottery, earthenware, most functional vessels

Secondary Clay is Usually Better for Pottery

The geological transport process grinds particles finer and sorts out larger fragments, producing a naturally refined, plastic clay body. Most historic pottery traditions were built on secondary clay deposits.

Where to Look

High-Probability Locations

Location	Why Clay Is Here	What to Expect
River banks (cut banks on outside of bends)	Erosion exposes clay layers deposited by past floods	Secondary clay; often fine and plastic; may contain organic matter
Lake shores and dried lakebeds	Still-water deposition concentrates fine clay particles	Very fine, plastic clay; may be high in organic matter
Road cuts and construction excavations	Expose buried clay layers	Variable; check the exposed strata for distinct clay bands
Cliff faces and erosion gullies	Natural erosion reveals geological layers	Look for smooth, slippery bands distinct from surrounding rock or soil
Stream beds	Water has sorted material by size	Fine sediment in slow-moving sections; coarser near fast water
Under topsoil (30-100 cm depth)	Clay subsoil layer common in many soil types	Dig test pits; watch for color and texture change below the root zone
Flood plains	Periodic flooding deposits fine sediment	Wide, flat areas near rivers; often excellent secondary clay

Landscape Indicators

These environmental clues suggest clay is present below the surface:

1. Puddles that persist for days after rain — clay is impermeable and traps water
2. Cracked, polygonal mud patterns when dry — only clay does this
3. Slippery patches on trails or hillsides when wet — clay lubricated by water
4. Sparse vegetation in patches surrounded by healthy growth — clay subsoil is difficult for roots
5. Spring lines on hillsides where water seeps out — water often flows along the top of clay layers
6. Ant hills and termite mounds — these insects often excavate clay from depth and deposit it on the surface
7. Burrowing animal holes — check the excavated dirt for clay content

Geological Settings

If you have any knowledge of the local geology:

• Glacial deposits: Glaciers grind rock to fine particles; glacial lake deposits (varved clays) can be excellent
• Alluvial fans: Where streams emerge from mountains onto plains, they drop sediment by size — fine clay at the edges
• Shale outcrops: Shale is compressed ancient clay; it can sometimes be re-hydrated and used (soak in water for weeks, then process)
• Volcanic areas: Decomposed volcanic ash produces bentonite and other clay minerals
• Swamps and bogs: Clay often underlies organic deposits

Field Collection

Tools Needed

• A digging stick, shovel, or any pointed tool
• Containers for samples (baskets, bags, pots)
• Water for field testing
• A knife or sharp edge for cut tests

Sampling Procedure

1. Dig a test pit at a promising location. Go at least 30-50 cm below the surface — topsoil is mixed with organic matter and isn’t useful.
2. Identify the clay layer — it will look and feel distinctly different from topsoil above and rock or sand below. Clay is smooth, dense, and slightly sticky even when damp.
3. Take samples from multiple depths within the clay layer. Properties can vary significantly even within a single deposit.
4. Collect samples from multiple locations at least 10-20 meters apart to assess the deposit’s consistency.
5. Record the location relative to landmarks you can find again. Note the depth of the clay layer, its thickness, and what’s above and below it.

Field Tests

Perform these quick tests on-site to determine if a sample is worth processing:

The Squeeze Test: Wet a handful of the material and squeeze it in your fist. Open your hand:

• Clay: Holds the shape of your fist clearly, with finger impressions
• Silt: Partially holds shape, crumbles at edges
• Sand: Falls apart immediately

The Shine Test: Cut a lump of moist clay with a knife and examine the cut surface:

• Clay: Smooth, shiny cut surface
• Silt: Dull, slightly rough surface
• Sand: Visible grains, rough texture

The Ribbon Test: Squeeze a moistened ball into a flat ribbon between thumb and forefinger:

• Over 5 cm before breaking: Good pottery clay candidate
• 3-5 cm: Moderate; may need blending
• Under 3 cm: Too lean for pottery without significant modification

The Taste/Bite Test: Place a small piece between your front teeth:

• Smooth, no grit: Clay-dominant — excellent
• Slightly gritty: Mixed clay and silt — usable
• Crunchy/gritty: Too much sand or silt — poor candidate

Don't Taste Unknown Soils in Contaminated Areas

Near old industrial sites, mining areas, or waste dumps, soils may contain heavy metals or chemicals. In a post-collapse world, most contamination would be pre-existing. Use the squeeze and ribbon tests instead.

Evaluating Deposit Quality

Deposit Size

A single potter working steadily uses roughly 500-1,000 kg of raw clay per year. A community pottery operation might need several tons annually. Evaluate whether a deposit can sustain long-term production:

• Estimate the exposed clay volume (length x width x depth of the clay layer)
• Remember that only 50-70% of raw clay becomes usable after processing (removing rocks, roots, and excessively sandy sections)
• A deposit 2 meters wide, 1 meter thick, and 10 meters long contains roughly 20 cubic meters — about 30-40 tons of clay. This would supply a small community for decades.

Accessibility

Consider practical factors:

• Distance from settlement — clay is heavy; long transport is laborious
• Year-round access — does the site flood seasonally? Freeze? Become impassable?
• Digging difficulty — soft secondary clay is easier to extract than hard primary deposits
• Water availability nearby — you’ll need water for processing, and hauling water is as costly as hauling clay

Renewability

Clay deposits renew extremely slowly on human timescales (geological time). However:

• River-deposited clays are continuously renewed by flooding — the deposit grows with each flood season
• Lakebeds and floodplains often contain vast reserves far exceeding what any community could exhaust
• Even “finite” deposits are typically so large that exhaustion isn’t a practical concern for generations

Processing Decisions Based on Source

Clay Source	Likely Processing Needed
River bank, fine-grained	Screen for debris; may be usable with minimal processing
Lake bed	Remove organic matter; may need temper addition
Subsoil deposit	Screen and possibly slake; add temper
Weathered granite (kaolin)	Wash and levitate to remove rock fragments; blend with secondary clay for plasticity
Shale	Extended soaking, crush, slake, screen — most labor-intensive
Termite/ant mound material	Often already well-processed by the insects; test directly

Building a Clay Library

As you explore your area, collect and label samples from every potential deposit. For each sample:

1. Fire a small test tile at your standard kiln temperature
2. Record: source location, color wet, color dried, color fired, plasticity (ribbon test length), shrinkage
3. Store labeled samples and test tiles together
4. Over time, you’ll build a map of your area’s clay resources — knowing which deposit produces the best cooking-pot clay, which works for storage jars, and which makes reliable crucibles

This clay library becomes invaluable knowledge. When one deposit is depleted or inaccessible, you’ll know exactly where to go next. And when you need a specific property — high refractoriness for crucibles, high plasticity for thin-walled throwing — you’ll know which source provides it without months of trial and error.

Finding clay is exploration, geology, and materials science rolled into one. Invest the time early, and your community’s pottery production will rest on a foundation of reliable, well-understood raw materials for generations to come.