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 Ash and Native-Material Glazes
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

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

Unwanted Crystallization in a Cone 6 Glaze

Description

Someone is having a problem with a cone 6 glaze going glossy and crystallizing, this article rationalizes the problem in terms of chemistry

Article

Following is a letter we got from someone who was wondering whether glaze software could help fix a glaze problem:

The main thing I am trying to fix currently is this: I have a Cone 6 base that I like very much, but it sometimes goes a little glossy and crystallizes on me. Here is the recipe:

      Potash feldspar 39.0
      Zinc Oxide  25.0
      Whiting  16.1
      Flint  14.2
      Kaolin (EPK) 6.7

A friend suggested I try Neph Sy in place of the feldspar and/or replacing the Zinc Oxide with tin oxide. I can't tell where to look in the program or website to tell if either of these or both would help or if I need to do something else. Can you direct me to the right place? Thanks for you help.

If you put this recipe into your account at insight-live.com and then open a typical cone 6 target formula beside it you will see that the zinc is more than double the recommended maximum. If you research ZnO (by clicking its oxide name) you will see that it causes crystallization and is of course a strong flux.

 CaO       0.31*
 MgO       0.00*
 K2O       0.13*
 ZnO       0.56* Target 0-0.2
 TiO2      0.00 
 Al2O3     0.17 Target 0.25-0.5
 SiO2      1.27 Target 2.5-4.0

You will also see that Al2O3 and SiO3 are dramatically lower than the minimum recommended. Alumina gives the glaze body and silica is the glass. If these are low the glaze will run and be soft and easily scratched and disollved by acids.

Crystalline glazes are low in alumina and high in zinc. However they need silica to form silicate crystals and the lack of silica in your glaze explains why you did not get crystals all the time. You probably got them when you cooled slower and gave them a chance to grow or when the glaze was able to obtain SiO2 from the body or an underglaze or a stain. Your glaze is probably going glossy when the circumstances are right for zinc to also impose its personality as a flux.

Your problem is a classic example of when you need to learn the function of the ten or so oxides from which the fired glass is built and to see glazes as oxides rather than materials. Insight-live.com makes it easy to convert a recipe to a formula of oxides and back again.

Your friends idea of replace zinc with tin is curious. Zinc is a flux, tin is a refractory opacifier. Also Nepheline and feldspar are quite similar materials. Nepheline has more alumina so that might have impeded the crystals a bit but the glaze would still have been dramatically off balance and subject to scratching, leaching and running.

Related Information

Links

Oxides ZnO - Zinc Oxide

By Tony Hansen


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