Levigation

Part of Pigments and Paint

Purifying and grading pigments through water-based settling (levigation).

Why This Matters

Raw pigment materials — dug from the earth, scraped from rocks, or produced by chemical reactions — are rarely pure or uniform. They contain sand, clay, organic debris, and particles of wildly different sizes. Levigation is the technique that transforms these crude materials into paint-grade pigment by exploiting a simple physical principle: in water, heavy and coarse particles sink fast while fine particles sink slowly.

In a rebuilding scenario, levigation is essential because it requires no specialized equipment — only water, containers, and patience. It simultaneously accomplishes two things that would otherwise require separate processes: purification (removing non-pigment contaminants) and grading (sorting particles by size). A single levigation session can separate crude ochre into ultra-fine artist-grade pigment, medium-grade paint pigment, and coarse material suitable for pottery glaze or construction filler.

This technique applies beyond pigments. The same principle is used to refine clay for pottery, purify medicite powders, separate gold dust from sand, and grade abrasive powders. Mastering levigation gives you a versatile separation tool applicable across multiple crafts.

The Principle

Levigation relies on Stokes’ Law: the settling velocity of a particle in a fluid depends on its size and density. In practical terms:

• Large, heavy particles sink to the bottom within seconds
• Medium particles settle over minutes to hours
• Fine particles remain suspended for hours to days
• Ultra-fine particles may stay suspended for weeks

By decanting (pouring off) the water at timed intervals, you collect particles of progressively finer size. Each fraction is a different grade of pigment.

Density Matters Too

Levigation separates by settling rate, which depends on both size and density. A small, dense particle (like cinnabar) settles at the same rate as a larger, lighter particle (like chalk). This is actually useful — it automatically sorts out lightweight contaminants like plant matter and organic debris, which float or settle very slowly.

Equipment

You need only basic containers:

Item	Purpose	Alternatives
Large ceramic bowl or bucket	Mixing vessel	Any waterproof container
3-5 smaller containers	Receiving vessels for fractions	Jars, pots, wooden bowls
Clean water	Suspension medium	Rainwater preferred (no minerals)
Stirring stick	Agitation	Any smooth stick
Fine cloth	Final straining	Linen, cotton, or woven grass
Flat drying surface	Drying the fractions	Stone slab, wooden board, ceramic plate

The Levigation Process

Step 1: Initial Preparation

1. Crush your raw pigment material to coarse powder in a mortar and pestle — pieces should be no larger than sand grains
2. Place the crushed material in your large mixing vessel
3. Add water at a ratio of approximately 10 parts water to 1 part pigment by volume
4. Stir vigorously for 2-3 minutes to fully wet all particles and break up any clumps

Step 2: First Settling (Remove Coarse Impurities)

1. Let the mixture stand for 30-60 seconds
2. Large sand grains, stone fragments, and heavy debris will settle to the bottom
3. Carefully pour the cloudy water (with suspended fine particles) into your first receiving container
4. Discard the sediment at the bottom — this is waste material

Step 3: Second Settling (Medium Grade)

1. Let the decanted liquid stand for 10-15 minutes
2. Medium-sized pigment particles settle during this period
3. Carefully pour the still-cloudy water into a second receiving container
4. The sediment in the first receiving container is your medium-grade pigment
5. Let this sediment settle fully, pour off excess water, and set aside to dry

Step 4: Third Settling (Fine Grade)

1. Let the second container stand for 2-4 hours (or overnight)
2. Fine pigment particles settle during this period
3. Pour off the remaining water — it may still be slightly tinted
4. The sediment is your fine-grade pigment — the most valuable fraction for painting

Step 5: Ultra-Fine Recovery (Optional)

1. The water poured off in Step 4 still contains ultra-fine particles
2. Let it stand undisturbed for 24-48 hours
3. Carefully decant the clear water
4. The thin layer of sediment is ultra-fine pigment, suitable for watercolor-type applications

Multiple Passes

For the highest purity, repeat the process on each fraction. Take your fine-grade pigment, re-suspend in water, and re-settle. Each pass removes more impurities and produces more uniform particle size.

Drying and Collecting

After levigation, each fraction is a wet slurry that must be dried:

1. Pour the settled slurry onto a flat, absorbent surface (unglazed ceramic, wood, or stone)
2. Spread thinly — no more than 3-4 mm thick
3. Dry in shade (direct sun can alter some pigment colors)
4. Drying time depends on humidity: 1-3 days typically
5. Once fully dry, scrape up the pigment cake and crumble it into powder
6. Store in labeled containers

Wind Protection

Fine pigment powder blows away easily during drying. Cover with a loosely draped cloth that allows airflow but blocks wind. Alternatively, dry indoors near a window.

Levigation for Specific Pigments

Earth Pigments (Ochres, Umbers, Siennas)

Earth pigments benefit enormously from levigation:

• Raw ochre dug from the ground contains 30-70% non-pigment material (sand, clay, gravel)
• First settling removes all gravel and coarse sand
• Fine fraction after 4-hour settling is pure iron oxide pigment
• Color often improves dramatically — levigated ochre is brighter and more saturated than crude ochre
• Yields vary: expect 20-50% of raw material weight as usable pigment

Chalk and Whiting

White pigments require careful levigation to achieve the smoothness needed for gesso and white paint:

• Crush chalk to coarse powder
• Use a very tall, narrow container — the deeper the water column, the better the separation
• First settle for 2 minutes to remove sand and grit
• Final settle for 6-12 hours to collect ultra-fine chalk
• The ultra-fine fraction makes excellent gesso and smooth white paint

Mineral Pigments (Malachite, Azurite, Cinnabar)

Precious mineral pigments require special care because particle size directly affects color:

• Azurite: Coarse particles are deep blue; fine particles become pale. Collect the medium fraction (5-15 minutes settling) for the richest blue
• Malachite: Similar to azurite — medium grind produces the best green
• Cinnabar: Dense mineral; settles quickly. Use very brief first settling (15-30 seconds) to separate from rock matrix, then collect the 5-minute fraction

Charcoal and Lamp Black

Carbon pigments are very light and require modified technique:

• Carbon floats initially due to surface tension — add a tiny drop of dissolved soap or alcohol to break the surface tension
• Use less water (5:1 ratio) for better control
• First settling is very brief (10-15 seconds) to remove non-carbon debris
• Fine carbon may take 24+ hours to settle — patience required

Advanced Techniques

Washing

Washing is a variant of levigation focused on removing soluble impurities rather than sizing particles:

1. Suspend the pigment in water and stir
2. Let all particles settle completely
3. Pour off the water (which now contains dissolved salts and soluble contaminants)
4. Repeat 3-5 times with fresh water each time
5. The pigment is now free of soluble impurities

This is essential for pigments made by chemical precipitation (like Prussian blue or lead white) which retain soluble reaction byproducts.

Elutriation

Elutriation is continuous-flow levigation — water flows upward through a column of sediment, carrying fine particles out the top while coarse particles remain at the bottom:

1. Build a tall tube or funnel from clay, bamboo, or sheet metal
2. Pack the bottom with coarse gravel (as a support bed)
3. Add your crude pigment on top of the gravel
4. Slowly pour water through the top — it percolates through the gravel and pigment
5. Fine pigment overflows the top and is collected in a basin below
6. Adjust water flow rate to control the fineness of the separated pigment

This method is more efficient than batch levigation for processing large quantities.

Temperature Effects

Warm water reduces viscosity, allowing particles to settle faster. Cold water increases settling time. If you need to speed up levigation:

• Use water warmed to 40-50 degrees Celsius
• Settling times can be reduced by roughly half
• Do not use boiling water — some pigments are altered by heat

Quality Assessment

After levigation, test your pigment fractions:

1. Smoothness test: Rub between thumb and forefinger — fine fraction should feel like talcum powder, no grit whatsoever
2. Color test: Compare fractions — the finest fraction is often brighter but can be paler for some minerals
3. Tinting test: Mix a small amount with water and gum arabic, brush onto white paper. Assess coverage, color intensity, and smoothness
4. Purity test: Examine a thin smear under good light. Contaminating particles show as specks of different color

A well-levigated pigment, properly ground afterward, produces paint comparable to any factory product. The technique is simple but the results are transformative.