Monthly Tech-Tip from Tony Hansen SignUp

No tracking! No ads! That's why this page loads quickly!

200 mesh | 325 mesh | 3D Design | 3D Printer | 3D Slicer | 3D-Printed Clay | 3D-Printing | Abrasion Ceramics | Acidic Oxides | Agglomeration | Alkali | Alkaline Earths | Amorphous | Apparent porosity | Artware | Ball milling | Bamboo Glaze | Base Glaze | Base-Coat Dipping Glaze | Basic Oxides | Batch Recipe | Bisque | Bit Image | Black Coring | Bleeding colors | Blender Mixing | Blisters | Bloating | Blunging | Bone China | Borate | Boron Blue | Boron Frit | Borosilicate | Breaking Glaze | Brick Making | Brushing Glaze | Calcination | Calculated Thermal Expansion | Candling | Carbon Burnout | Carbon trap glazes | CAS Numbers | Casting-Jiggering | Celadon Glaze | Ceramic | Ceramic Binder | Ceramic Decals | Ceramic Glaze | Ceramic Glaze Defects | Ceramic Ink | Ceramic Material | Ceramic Oxide | Ceramic Slip | Ceramic Stain | Ceramic Tile | Ceramics | Characterization | Chemical Analysis | Chromaticity | Clay | Clay body | Clay Body Porosity | Clay for Ovens and Heaters | Clay Stiffness | Co-efficient of Thermal Expansion | Code Numbering | Coil pottery | Colloid | Colorant | Cone 1 | Cone 5 | Cone 6 | Cone plaque | Copper Red | Cordierite Ceramics | Crackle glaze | Crawling | Crazing | Cristobalite | Cristobalite Inversion | Crucible | Crystalline glazes | Crystallization | Cuerda Seca | Cutlery Marking | Decomposition | Deflocculation | Deoxylidration | Differential thermal analysis | Digitalfire Foresight | Digitalfire Insight | Digitalfire Reference Library | Dimpled glaze | Dip Glazing | Dipping Glaze | Dishwasher Safe | Dolomite Matte | Drop-and-Soak Firing | Drying Crack | Drying Performance | Drying Shrinkage | Dunting | Dust Pressing | Earthenware | Efflorescence | Encapsulated Stain | Engobe | Eutectic | Fast Fire Glazes | Fat Glaze | Feldspar Glazes | Fining Agent | Firebrick | Fireclay | Fired Strength | Firing Schedule | Firing Shrinkage | Flameware | Flashing | Flocculation | Fluid Melt Glazes | Flux | Food Safe | Foot Ring | Forming Method | Formula Ratios | Formula Weight | Frit | Fritware | Functional | GHS Safety Data Sheets | Glass vs. Crystalline | Glass-Ceramic Glazes | Glaze Bubbles | Glaze Chemistry | Glaze Compression | Glaze Durability | Glaze fit | Glaze Gelling | Glaze laydown | Glaze Layering | Glaze Mixing | Glaze Recipes | Glaze Shrinkage | Glaze thickness | Globally Harmonized Data Sheets | Glossy Glaze | Green Strength | Grog | Gunmetal glaze | Handles | High Temperature Glaze | Hot Pressing | Incised decoration | Industrial clay body | Ink Jet Printing | Inside-only Glazing | Insight-Live | Interface | Iron Red Glaze | Jasper Ware | Jiggering | Kaki | Kiln Controller | Kiln Firing | Kiln fumes | Kiln venting system | Kiln Wash | Kovar Metal | Laminations | Leaching | Lead in Ceramic Glazes | Leather hard | Lime Popping | Limit Formula | Limit Recipe | Liner Glaze | Liner glazing | Liquid Bright Colors | LOI | Low Temperature Glaze | Majolica | Marbling | Material Substitution | Matte Glaze | Maturity | Maximum Density | MDT | Mechanism | Medium Temperature Glaze | Melt Fluidity | Melting Temperature | Metal Oxides | Metallic Glazes | Micro Organisms | Microwave Safe | Mineral phase | Mineralogy | Mocha glazes | Mohs Hardness | Mole% | Monocottura | Mosaic Tile | Mottled | Mullite Crystals | Native Clay | Non Oxide Ceramics | Oil-spot glaze | Once fire glazing | Opacifier | Opacity | Ovenware | Overglaze | Oxidation Firing | Oxide Formula | Oxide Interaction | Oxide System | Particle orientation | Particle Size Distribution | | PCE | Permeability | Phase Diagram | Phase Separation | Physical Testing | Pinholing | Plainsman Clays | Plaster Bat | Plaster table | Plasticine | Plasticity | Plucking | Porcelain | Porcelaineous Stoneware | Pour Glazing | Powder Processing | Precipitation | Primary Clay | Primitive Firing | Propane | Propeller Mixer | Pugmill | Pyroceramics | Pyrometric Cone | Quartz Inversion | Raku | Reactive Glazes | Reduction Firing | Reduction Speckle | Refiring Ceramics | Refractory | Refractory Ceramic Coatings | Representative Sample | Respirable Crystalline Silica | Restaurant Ware | Rheology | Rutile Glaze | Salt firing | Sanitary ware | Sculpture | Secondary Clay | Shino Glazes | Shivering | Sieve | Sieve Shaker | Silica:Alumina Ratio | Silk screen printing | Sintering | Slaking | Slip Casting | Slip Trailing | Slipware | Slurry | Slurry Processing | Slurry Up | Soaking | Soluble colors | Soluble Salts | Specific gravity | Splitting | Spray Glazing | Stain Medium | Stoneware | Stull Chart | Sulfate Scum | Sulfates | Surface Area | Surface Tension | Suspension | Tapper Clay | Tenmoku | Terra Cotta | Terra Sigilatta | Test Kiln | Theoretical Material | Thermal Conductivity | Thermal shock | Thermocouple | Thixotropy | Throwing | Tony Hansen | Toxicity | Trafficking | Translucency | Transparent Glazes | Triaxial Glaze Blending | Ultimate Particles | Underglaze | Unity Formula | Upwork | Variegation | Viscosity | Vitreous | Vitrification | Volatiles | Warping | Water in Ceramics | Water Smoking | Water Solubility | Wedging | Whiteware | Wood Ash Glaze | Wood Firing | Zero3 | Zero4 | Zeta Potential

Particle Sizes

In ceramics, discussion about particle size most often focusses on clays and clay bodies. Fine particle sizes are associated with clean-burning and plastic clays, coarser ones with structural and sculpture bodies. Clays have already been processed by nature and have small particle sizes (those are agglomerated into the lumps we dig out of the ground), whereas other ceramic minerals have to be ground into a powder, often by massive machinery. Amazingly, the sizes, populations and relative populations in a ceramic powder can be measured physically using sieves and ultimately using lab equipment. Their shapes and surface topologies can also be characterized.

While a plastic clay might feel smooth to the touch it is actually millions of tiny rocks particles held together by the water. Clay particles have an affinity for water, they hold on to it like mini-magnets. And they are generally flat. The finer the particles the greater surface area they can expose to water and the greater will be the plasticity of the clay. When a piece of plastic clay is dried and put into water it will slake down, the individual particles are liberated. If propeller-mixed that slaked clay becomes a slurry and it can be poured through a screen (or sieve). Of course, any particles it contains will be filtered out by the sieve. That means we can weigh the oversize and compare that to the total amount to get a percentage.

Typical clays that might seem very fine can contain a surprising amount of larger particles. Sugar, for example, is around 40 mesh (that is a sieve with 40 wires-per-inch with openings measuring about 400 microns on-a-side). But many clays contain significant populations of particles that are double or triple that size. And they can contain particles that are incredibly small. 90%+ of some raw clays can be slaked and will pass a 325 mesh sieve (that is 325 wires-per-inch with openings of 45 microns, an average human hair is 70 microns). But those are physical particles, ones that we can measure on a sieve. But that 90% that passes the 325 sieve is ultimate particles, much finer, down to sub-micron sizes (a white blood cell is 25 microns)! Bentonite particles are the smallest (less than a micron), then ball clay and finally kaolin (up to 10 microns).

With glazes and enamels much effort goes into particle size reduction, this improves the working and fired properties. Typically there is less emphasis on measuring sizes than on production-testing to deduce the suitability (and increasing or decreasing grinding time, e.g. by ball milling, accordingly).

Related Information

How small can clay crystals be?

Tap picture for full size
Salt on a 60 mesh sieve, some goes through some does not

These are table salt crystals on a 60 mesh sieve. It has an opening of 250 micro meters (or microns). Half of the crystals passed this sieve, half are retained. Notice on the right, several crystals are in the openings, about to fall through. Imagine that a particle (or crystal) of bentonite or ball clay can be sub-micron in diameter, they can actually be 2500 times smaller on a side than these salt crystals! One-tenth-micron ultimate particles would thus fit 2500x2500 on the flat side of a salt crystal. And, since the clay crystal is much thinner than wide, perhaps ten could stack to the same dimension. That means theoretically 2500x2500x25000 (or 1 with eleven zeros) could pack into a grain of salt!

This is what labs use to measure particle size

Tap picture for full size
Two example of high quality brass laboratory sieves

To measure particle size in a slurry or powder you need sieves. This is the most popular type used in labs. They are made from brass by a company named Tyler. The range of screen sizes for testing particle size is very wide (obvious here: the top screen has an opening of 56 mm, the bottom one 0.1 mm - the wires are almost too small to see). You can often buy these used on Ebay for a lot less than new ones, search for "tyler sieve". The finer sieves (especially 200) are fragile and more easily ripped. It is good to have a 50, 100 and 150.

Grog particles having a narrow particle size range

Tap picture for full size

A closeup of 35-48 mesh grog particles (courtesy of Plainsman Clays). Grogs are added to clay bodies to impart better drying properties. Grog particles perform their drying-shrinkage-reducing function (for plastic bodies) best when they have an angular rather than round shape.

Washing EP kaolin through screens in particle size test.

Tap picture for full size

We measure 50 or 100 grams of powder, mix it in water and then wash it through sieves of varying openings. The finer particles go through, we dry and weigh the coarser ones that do not.

The same clay in lump and powder form. Which is heavier?

Tap picture for full size
The same clay in lump and powder form

Which one of these samples weighs more, the raw lump form of the clay or after it has been ground into a powder? Wrong. It is the lumps. Even though there is all that empty air space between those lumps, there is even more air spaces in the powder. The top one weighs 1662 grams (there is a 500g counter-weight barely visible), the bottom one is 1255. The finer I grind it the lighter it will be. If I were to fill in all the voids between the lumps on the top one with smaller sized lumps I could get alot more weight yet! It works the same on the ultimate particle level, when we combine powders of varying particle sizes we get a more dense and stronger dried product.

How fast will Veegum settle in water?

Tap picture for full size

This is VeeGum T, a processed smectite clay (similar to bentonite, extremely small particle size). I have propeller-mixed enough powder into water that it has begun to gel. How long does it take for them to begin to settle? Never. This sat for a month with no visible change! That means it is colloidal.


Glossary Powder Processing
An entire industry is dedicated to the science, materials and equipment associated with the handling of powders.
Glossary Ultimate Particles
Utlimate particles of ceramic materials are finer than can be measured even on a 325 mesh screen. These particles are the key players in the physical presence of the material.
Glossary Particle Size Distribution
Knowing the distribution of particle sizes in a ceramic material is often very important in assessing its function and suitability for an application.
Vibrating screens for industrial glaze preparation
By Tony Hansen
Follow me on

Got a Question?

Buy me a coffee and we can talk, All Rights Reserved
Privacy Policy