A Low Cost Tester of Glaze Melt Fluidity
A One-speed Lab or Studio Slurry Mixer
A Textbook Cone 6 Matte Glaze With Problems
Adjusting Glaze Expansion by Calculation to Solve Shivering
Alberta Slip, 20 Years of Substitution for Albany Slip
An Overview of Ceramic Stains
Are You in Control of Your Production Process?
Are Your Glazes Food Safe or are They Leachable?
Attack on Glass: Corrosion Attack Mechanisms
Ball Milling Glazes, Bodies, Engobes
Binders for Ceramic Bodies
Bringing Out the Big Guns in Craze Control: MgO (G1215U)
Ceramic Glazes Today
Ceramic Material Nomenclature
Ceramic Tile Clay Body Formulation
Changing Our View of Glazes
Chemistry vs. Matrix Blending to Create Glazes from Native Materials
Concentrate on One Good Glaze
Cone 6 Floating Blue Glaze Recipe
Copper Red Glazes
Crazing and Bacteria: Is There a Hazard?
Crazing in Stoneware Glazes: Treating the Causes, Not the Symptoms
Creating a Non-Glaze Ceramic Slip or Engobe
Creating Your Own Budget Glaze
Crystal Glazes: Understanding the Process and Materials
Deflocculants: A Detailed Overview
Demonstrating Glaze Fit Issues to Students
Diagnosing a Casting Problem at a Sanitaryware Plant
Drying Ceramics Without Cracks
Duplicating Albany Slip
Duplicating AP Green Fireclay
Electric Hobby Kilns: What You Need to Know
Fighting the Glaze Dragon
Firing Clay Test Bars
Firing: What Happens to Ceramic Ware in a Firing Kiln
First You See It Then You Don't: Raku Glaze Stability
Fixing a glaze that does not stay in suspension
Formulating a Clear Glaze Compatible with Chrome-Tin Stains
Formulating a Porcelain

Formulating Your Own Clay Body
G1214M Cone 5-7 20x5 Glossy Base Glaze
G1214W Cone 6 Transparent Base Glaze
G1214Z Cone 6 Matte Base Glaze
G1916M Cone 06-04 Base Glaze
G1947U/G2571A Cone 10/10R Base Matte/Glossy Glazes
Getting the Glaze Color You Want: Working With Stains
Glaze and Body Pigments and Stains in the Ceramic Tile Industry
Glaze Chemistry Basics - Formula, Analysis, Mole%, Unity, LOI
Glaze chemistry using a frit of approximate analysis
Glaze Recipes: Formulate Your Own Instead
Glaze Types, Formulation and Application in the Tile Industry
Having Your Glaze Tested for Toxic Metal Release
High Gloss Glazes
How a Material Chemical Analysis is Done
How desktop INSIGHT Deals With Unity, LOI and Formula Weight
How to Find and Test Your Own Native Clays
How to Liner-Glaze a Mug
I've Always Done It This Way!
Inkjet Decoration of Ceramic Tiles
Interpreting Orton Cones
Is Your Fired Ware Safe?
Leaching Cone 6 Glaze Case Study
Limit Formulas and Target Formulas
Low Budget Testing of the Raw and Fired Properties of a Glaze
Low Fire White Talc Casting Body Recipe
Make Your Own Ball Mill Stand
Making Glaze Testing Cones
Monoporosa or Single Fired Wall Tiles
Organic Matter in Clays: Detailed Overview
Outdoor Weather Resistant Ceramics
Overview of Paper Clay
Painting Glazes Rather Than Dipping or Spraying
Particle Size Distribution of Ceramic Powders
Porcelain Tile, Vitrified or Granito Tile
Rationalizing Conflicting Opinions About Plasticity
Ravenscrag Slip is Born
Recylcing Scrap Clay
Reducing the Firing Temperature of a Glaze From Cone 10 to 6
Single Fire Glazing
Soluble Salts in Minerals: Detailed Overview
Some Keys to Dealing With Firing Cracks
Stoneware Casting Body Recipes
Substituting Cornwall Stone
Super-Refined Terra Sigillata
The Chemistry, Physics and Manufacturing of Glaze Frits
The Effect of Glaze Fit on Fired Ware Strength
The Four Levels on Which to View Ceramic Glazes
The Majolica Earthenware Process
The Physics of Clay Bodies
The Potter's Prayer
The Right Chemistry for a Cone 6 MgO Matte
The Trials of Being the Only Technical Person in the Club
The Whining Stops Here: A Realistic Look at Clay Bodies
Those Unlabelled Bags and Buckets
Tiles and Mosaics for Potters
Toxicity of Firebricks Used in Ovens
Trafficking in Glaze Recipes
Understanding Ceramic Materials
Understanding Ceramic Oxides
Understanding Glaze Slurry Properties
Understanding the Deflocculation Process in Slip Casting
Understanding the Terra Cotta Slip Casting Recipes In North America
Understanding Thermal Expansion in Ceramic Glazes
Unwanted Crystallization in a Cone 6 Glaze
Variegating Glazes
Volcanic Ash
What Determines a Glaze's Firing Temperature?
What is a Mole, Checking Out the Mole
What is the Glaze Dragon?
Where Do I Start?
Why Textbook Glazes Are So Difficult

Formulating Ash and Native-Material Glazes


How to have a volcanic ash analysed and them use ceramic chemistry to create a glaze that contains the maximum possible amount of the ash for the desired effect


To most new potters, the idea of creating your own volcanic ash glaze is really quite romantic. Unfortunately, the actual job of trying to produce one that is reasonably functional is not quite so exotic.

Many textbooks supply recipes that employ volcanic ash, but the results of force fitting your ash into these could prove to be a real time waster. Even using a textbook recipe as a simple trial and error starting point, often ends up in blind allies that go nowhere.

The most foolproof way to develop a base glaze is to use calculation, even for native materials like ash. When you view recipes as combinations of oxides, and materials as "sources" of these oxides, suddenly there are an infinite number of material combinations (or recipes) that will yield a target formula. Each of these recipes will fire with subtle differences but in other respects they will be very similar. Having a formula for your ash will thus give it equal status with any other material you have. But where can you obtain the formula for your ash? It is true that some books list a range of ash formulas. "Electric Kiln Pottery" is an example, it has a dizzying list of ash formulas of incredible variation in oxide chemistry. But picking one that closely matches your material is like playing roulette. Don't bother. If you bought the material, I recommend contacting the manufacturer to get the analysis. If not, spend the $50 and have the ash analysed at a lab.

As a demonstration, I dug out a good-sized sample of volcanic ash from a six-inch thick seam at a local clay quarry (vintage Crater Lake volcanic eruption). I mixed the pile thoroughly with a shovel to assure easy sampling of a specimen which was representative of the entire supply. I sent a small amount of the material to a lab for a simple analysis to determine the amounts of each significant ceramic oxide. Finally, I keyed this into INSIGHT and inserted it into the program's materials database, making it available for reference in future recipes entered.

Following is a formula calculation report of the material.

DETAIL PRINT - Oxide Analysis
MATERIAL               PARTS  WEIGHT   CaO*   MgO*   K2O*  Na2O* Fe2O3*   TiO2   P2O5  Al2O3   SiO2
WEIGHT OF EACH OXIDE                   56.1   40.3   94.2   62.0  160.0   79.7  142.0  102.0   60.1
---------------------------------------------------------------------------------------------------  MATERIAL
Expan OF EACH OXIDE                    0.15   0.03   0.33   0.39   0.13   0.14   0.00   0.06   0.04   Cost/kg
---------------------------------------------------------------------------------------------------  -------
 CaO................    8.04   56.10   0.14                                                             0.15
 Na2O...............    0.10   62.00                        0.00                                        0.39
 K2O................    0.30   94.20                 0.00                                               0.33
 TiO2...............    0.04   79.70                                      0.00                          0.14
 Fe2O3..............    1.00  160.00                               0.01                                 0.13
 MgO................    0.72   40.30          0.02                                                      0.03
 SiO2...............   72.84   60.10                                                           1.21     0.04
 Al2O3..............    2.06  102.00                                                    0.02            0.06
 P2O5...............    0.02  142.00                                             0.00                   0.00
---------------------------------------------------------------------------------------------------  -------
TOTAL                  85.12           0.14   0.02   0.00   0.00   0.01   0.00   0.00   0.02   1.21     0.05
UNITY FORMULA                          0.83   0.10   0.02   0.01   0.04   0.00   0.00   0.12   7.04
PER CENT BY WEIGHT                     8.09   0.72   0.30   0.10   1.01   0.04   0.02   2.07  73.27
Cost/kg  0.05
 L.O.I. 14.38
  Si:Al 60.01
 SiB:Al 60.01
  Expan  4.88

To use as much ash in the recipe as possible, I proceeded as follows:

Cone 6 Limit Formulae
CaO 0.1-0.7 Al2O3 0.2-0.35
ZnO -0.2 B2O3 -0.45
BaO -0.3 SiO2 2-3.5
MgO -0.3    
KNaO 0.1-0.5    

Following is the final recipe and its calculation.

INSIGHT's interactive nature and instant calculation made it easy to juggle different amounts of dolomite and kaolin until the formula was right.

MATERIAL               PARTS  WEIGHT    CaO    MgO    K2O   Na2O  Fe2O3   TiO2   P2O5  Al2O3   SiO2
WEIGHT OF EACH OXIDE                   56.1   40.3   94.2   62.0  160.0   79.7  142.0  102.0   60.1
---------------------------------------------------------------------------------------------------  MATERIAL
Expan OF EACH OXIDE                    0.15   0.03   0.33   0.39   0.13   0.14   0.00   0.06   0.04   Cost/kg
---------------------------------------------------------------------------------------------------  -------
 PUMICITE...........   60.00  577.23   0.09   0.01   0.00   0.00   0.00   0.00   0.00   0.01   0.73     0.00
 DOLOMITE...........   20.00  184.00   0.11   0.11                                                      0.00
 KAOLIN.............   20.00  258.14                                                    0.08   0.15     0.24
---------------------------------------------------------------------------------------------------  -------
TOTAL                 100.00           0.20   0.12   0.00   0.00   0.00   0.00   0.00   0.09   0.89     0.05
UNITY FORMULA                          0.20   0.12   0.00   0.00   0.00   0.00   0.00   0.09   0.89
PER CENT BY WEIGHT                    13.85   6.09   0.22   0.07   0.76   0.03   0.02  11.57  67.39
Cost/kg  0.05
  Si:Al  9.89
 SiB:Al  9.89
  Expan  5.50

The whole process took only a couple of minutes. The next step was mixing up the glaze and trying it. I soon found that the ash was very hard, and the glaze had to be ball milled. But once milled, its thixotropic consistency was beautiful and it applied to the ware very well. This was an unexpected bonus! I fired to cone 6, 7, 8, 9, and 10, and found it to be a beautiful crystal tan bamboo at cone 8-9.

When a glaze is completed using this method, it has a balanced formula, one that is less likely to dissolve in acids, scratch on metal, chip on impact, or craze or shiver on heat shock. This volcanic ash glaze is perfectly suitable on the finest dinner ware and I can mix ten gallons for a few dollars! As a balanced base, it is just waiting for some trial and error mixtures with opacifiers, crystal seeders, colorants, speckling agents, etc. While there are many ways to design a glaze, not too many meet with success on the very first trial the way this approach did.

Ball Mill

If you would like to really get into making glazes from your own materials, you will likely need a way to grind them. A ball mill is one of the best investments you can make. It will grind any glaze into a beautifully fine and silky slurry and will make it possible to use almost any material. Milled glazes will melt better and be more consistent and they will have fewer surface defects.

Related Information


Materials Wood Ash
Materials Volcanic Ash
Articles Ball Milling Glazes, Bodies, Engobes
Industries ball mill their glazes, engobes and even bodies as standard practice. Yet few potters even have a ball mill or know what one is.
Articles Duplicating Albany Slip
How Alberta Slip was created by analysing and duplicating the physical and chemical properties of Albany Slip
Glossary Native Clay

By Tony Hansen

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