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

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
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
Formulating a Clear Glaze Compatible with Chrome-Tin Stains
Formulating a Porcelain
Formulating Ash and Native-Material Glazes
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 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 Black Art of Drying Ceramics Without Cracks
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
Using Plaster Bats
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

Chemistry vs. Matrix Blending to Create Glazes from Native Materials

Description

Is it better to do trial and error line and matrix blending of materials to formulate your glazes or is it better to use glaze chemistry?

Article

Perhaps you have a material native to your area and want to create a glaze from it. Logically you want to maximize the amount used in the recipe. Or you are a student and have an assignment to create a glaze from a selection of materials available to you. It can be difficult to know where to start. Current wisdom suggests doing a matrix of blends with materials like feldspar, silica, kaolin, calcium carbonate, etc. After quite a bit of work you would hopefully find a mix that melts well and looks good. However this method has some serious issues when compared to a full-chemistry or chemistry-assisted approach.

First of all, a glaze is much more than 'looks'. There are a million blends that look well, but only a thousand that function well. Function? What about hardness, resistance to leaching, fit on your clay body, suspension and application properties, compatibility with coloring oxides, tendency to devitrify, blister, crawl, cloud, run, etc. Material level blenders tend to look at the visual and deal with this dizzying array of potential problems later. But a good glaze is a complex balance between working properties in production and physical properties of the fired result, this balance does not easily happen by tunnel-vision blending focused on the visual only. You cannot do blending to fix a crazing problem, for example; the high thermal expansion is a product of high Na2O or K2O, the materials in the glaze that contribute these oxides also contribute others that are critical to other aspects of the glaze That means fooling around with their percentages affects a lot more than just the thermal expansion. An example: the ceramic world is full of high-feldspar glazes that craze and settle like a rock in the bucket. Why? Because feldspar is the melter, and the trial blends employed to formulate these tended to crow-bar high percentages into the blend to get the rest of the concoction to melt into reactive glazes with good visuals. That produces crazing glazes. Chemistry looks at a glaze as a formula of oxides and there is a direct link between the way it fires and that formula. The materials are oxide sources. When one learns how to recognize what a formula should look like, he does not waste time going down blind allies that deviate wildly and bring a host of issues. Chemistry-blind approaches shut out the key characteristic we benefit most from knowing.

Consider an example of developing a recipe to use your own native materials in the highest possible percentage. It is a volcanic ash that I dug from a local quarry, I spent $30 and had it analyzed. Then I converted the analysis to a unity formula using Digitalfire desktop INSIGHT software. I'll dub it 'Elkwater Ash'.

  CaO    8.7% 0.86 molar
  Na2O   0.1  0.11
  K2O    0.3  0.02
  Fe2O3  1.1  0.04
  MgO    0.8  0.11
  SiO2  78.7  7.29
  Al2O3  2.2  0.12
  LOI   14.0

Notice now low the alumina is. This is very unusual. Also the silica is very high. The silica:alumina ratio is 60:1 (a glaze is typically 10:1). That means we definitely don't want to blend with materials that add silica but we do want ones that add alumina. Hmmm. No practical material qualifies. That means we will have to tolerate a material with lots of Alumina and minimal silica contribution. Kaolin fits the bill and it will suspend the slurry. Adding feldspar is thus out of the question, it contains far too much silica.

This material has a high CaO content, it will likely make a hard glaze, however high CaO can signal leaching problems. Also, if you know about formulas you'll see from this one that this material is low in flux. This will be worsened after kaolin is added. That means we need to blend it with materials that add fluxes other than CaO. That excludes whiting and dolomite.

As it turns out, it is possible to use up to 60% of this material in a glaze to melt around cone 7 (see the lesson link below, although dated because it refers to the old desktop Insight software, the principles of the chemistry are valid). Then some line blending could be done to fine tune additions of colorants, opacifiers and variegators to produce something with an interesting surface.

The typical approaches of blind line blending with the obvious calcium carbonate, dolomite, silica, and feldspar would all have gone in the wrong direction in this case. Could you possibly have achieved close to 60% of this material in a recipe by chemistry-blind-blending? Deal with all the above issues in parallel? Not likely. My point? We need access to many tools when formulating glazes. Chemistry should come first, then optional blending if needed to fine tune; this is the opposite of what is taught in most circles today! One great comment I saw on Facebook by Paul Haigh was: "Chemistry guides, experiment decides". Ignore the chemistry and you are missing a key guide, you deny yourself and your glaze alot of options. There are a lot of dots to be connected, if you take away the chemistry dots you can no longer visualize the whole picture, they are the majority. You can fix some problems simply by changing firing, but you can adapt to almost anything, including variability, with the control of the chemistry.

Links

Projects Oxides
Projects Materials
Glossary Wood Ash Glaze
Common washed wood ash has a chemistry akin to a ceramic glaze, so it can comprise significant percentages in a recipe. Plus it can produce unique visual effects.
Glossary Feldspar Glazes
Feldspar is a natural mineral that, by itself, is the most similar to a high temperature stoneware glaze. Thus it is common to see alot of it in glaze recipes. Actually, too much.
Glossary Glaze Chemistry
Glaze chemistry is the study of how the oxide chemistry of glazes relates to the way they fire. It accounts for color, surface, hardness, texturem, melting temperature, thermal expansion, etc.
Glossary Triaxial Glaze Blending
In ceramics many technicians develop and adjust glazes by blending two, three or even four l materials or glazes together to obtain new effects
Media Desktop Insight 4 - Add a Native Material to MDT, Build a Glaze

By Tony Hansen


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