3D Design | 3D Printer | 3D Slicer | 3D-Printed Clay | 3D-Printing | Abrasion Ceramics | Acidic Oxides | Agglomeration | Alkali | Alkaline Earths | Amorphous | Analysis | Apparent porosity | Bacteria, Mold on Clay | Ball milling | Bamboo Glaze | Base Glaze | Base-Coat Dipping Glazes | Basic Oxides | Batch Recipe | Binder | Bisque, bisquit firing | Bit Image | Black Coring | Bleeding colors | Blisters | Bloating | Blunging | Bone China | Borate | Boron Blue | Boron Frit | Borosilicate | Breaking Glaze | Brushing Glazes | Buff stoneware | Calcination | Calculated Thermal Expansion | Candling | Carbon Burnout | Carbon trap glazes | CAS Numbers | Casting-Jiggering | Celadon Glaze | Ceramic | Ceramic Decals | Ceramic Glaze | Ceramic Ink | Ceramic Material | Ceramic Oxide | Ceramic Slip | Ceramic Tile | Ceramics | Characterization | Chromaticity | Clay | Clay body | Clay Body Porosity | Clay Stiffness | Co-efficient of Thermal Expansion | Code Numbering | Coil pottery | Colloid | Colorant | Cone plaque | Copper Red | Cordierite Ceramics | Corning Ware, Pyroceramics, Pyrex | | Crank, plate setter | Crawling | Crazing | Cristobalite | Cristobalite Inversion | Crucible | Crystalline glazes | Crystallization | Cuerda Seca | Cutlery Marking | De-Airing Pugmill | Decomposition | Deflocculation | Deoxylidration | Digitalfire Foresight | Digitalfire Insight | Digitalfire Insight-Live | Dimpled glaze | Dimpling, Orange Peel | Dip Glazing | Dipping Glazes | Dishwasher Safe | Dolomite Matte | Drop-and-Soak Firing | Drying Crack | Drying Performance | Drying Shrinkage | Dunting | Dust Pressing | Earthenware | Efflorescence | Encapsulated Stains | Engobe | Eutectic | Fast Fire Glazes | Fat Glaze | Feldspar Glazes | Firebrick | Fireclay | Fired Strength | Firing | Firing Schedule | Firing Shrinkage | Flameware | Flashing | Flocculation | Fluid Melt Glazes | Flux | Food Safe | Foot Ring | Forming Method | Formula | 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 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 | Ink Jet Printing | Inside-only Glazing | Interface | Iron Red Glaze | Jasper Ware | Jiggering | Kaki | Kiln Controller | Kiln fumes | Kiln venting system | Kiln Wash | Laminations | Leaching | Lead in Ceramic Glazes | Leather hard | Lime Popping | Limit Recipe | Liner Glaze | LOI | Low Temperature Glaze Recipes | Lustre Colors | Majolica | Marbling | Material Substitution | Matte Glaze | Maturity | MDT | Mechanism | Medium Temperature Glaze | Melt Fluidity | Melting Temperature | Metallic Glazes | Microwave Safe | Mineralogy | Mocha glazes | Mole% | Monocottura, Monoporosa | Mosaic Tile | Mottled | Mullite Crystals | Non Oxide Ceramics | Normalization | Oil-spot glaze | Once fire glazing | Opacifier, Opacification | Opacity | Orton Cones | Ovenware | Overglaze | Oxidation Firing | Oxide Interaction | Oxide System | Particle orientation | Particle Size Distribution | PCE | Permeability | Phase Diagram | Phase Separation | Phase, phase changes | Physical Testing | Pinholing | Plasticine | Plasticity | Plucking | Porcelain | Pour Glazing | Precipitation | Primary Clay | Primitive Firing | Production Setup | Propane | Propeller Mixer | Pyroceramics | Quartz Inversion | Raku | Reactive Glazes | Reduction Firing | Reduction Speckle | Refractory | Refractory Ceramic Coatings | Representative Sample | Respirable Crystalline Silica | Rheology | Rutile Glaze | Salt, soda firing | Sanitary ware | Sculpture | Secondary Clay | Shino Glazes | Shivering | Sieve | Silica:Alumina Ratio (SiO2:Al2O3) | Silk screen printing | Sinter, sintering | Slake, Slaking | Slip Casting | Slip Trailing | Soaking | Soluble Colors, Sulfate Colors | Soluble Salts | Specific gravity | Splitting | Spray Glazing | Stain | Stoneware | Stull Chart | Sulfate Scum | Sulfates, Sulphates | Surface Area | Surface Tension | Suspension | Tapper Clay | Target Formula, Limit Formula | Tenmoku | Terra cotta | Terra Sigilatta | Theoretical Material | Thermal Conductivity | Thermal shock | Thermocouple, pyrometer | Thixotropy | Tony Hansen | Toxicity | Tranlucency | Translucency | Transparent Glazes | Triaxial Glaze Blending | Ultimate Particles | Underglaze | Unity Formula | Upwork | Vaporization | Viscosity | Vitrification | Volatiles | Warping | Water in Ceramics | Water Smoking | Water Solubility | Wedging, kneading | Wheel Bat | Whiteware | Wood Ash Glaze | Wood Firing | Zero3 | Zeta Potential

Crackle glaze

Crackle glazes are used on decorative ceramic ware. They have a crack pattern that is a product of thermal expansion mismatch between body and glaze.

Details

A type of ceramic glaze that is intentionally crazed. Crazing is a crack pattern caused by thermal expansion mismatch between body and glaze. After the glaze solidifies (as the kiln cools) it shrinks more than the body. To relieve the tension of being stretched, it cracks. Crackle glazes are typically found on ware fired at low temperatures. Stains and other colorants are often rubbed into the crack lines to heighten the effect.

Crackle glazes are best understood in terms of their oxide makeup, or chemistry. They almost always have very high levels of Na2O, and possibly K2O (collectively referred to as KNaO). These two oxides have the highest thermal expansion, by far, of those commonly found in ceramic materials. Feldspar is the key source. Not surprisingly, high feldspar glazes often crackle. Na2O is also present in the majority of frits. Some frits are formulated to have a high thermal expansion, these are invariably very high in Na2O (much higher than feldspar). Ferro Frit 3110 is an example, some raku crackle glazes have up to 90% of it! As firing temperature increases more kaolin and silica must be added (to source Al2O3 and SiO2) to reduce melt fluidity (and thus the tendency to run down off the ware).

You can control the amount of crackle (proximity of the crack lines) by varying the amount of KNaO-sourcing materials in the glaze recipe. For example, for low temperatures, you could employ a blend of Frit 3110 and 3195 to make up 85% of the recipe (the rest being kaolin). The more Frit 3195, the less the crazing will be. For even better control enter your recipe into your account at Insight-live.com (making sure materials are named correctly so they link to the database), it can display the unity formula. Move the KNaO up (while holding the proportions of other oxides constant) to increase crazing, down to reduce it.

Crackle glazes typically severely weaken ceramic ware, especially if it is thin walled (to the point it can be easily torn apart with your bare hands). Crackle glazes are definitely not suitable for functional ware (because of bacteria growth and leaching).

This is crazing. Really bad crazing!

This is crazing. Really bad crazing!

These two glazes look the same, they are both cone 6 satin mattes. On the same porcelain. But the matteness "mechanism" of the one on the left is a low Si:Al ratio melted by zinc and sodium. The mechanism of the one on the right is high MgO melted by boron (with the same Si:Al ratio). The "baggage" of the mechanism on the left is high thermal expansion. And crazing (which drastically reduces strength and provides a haven for bacteria). The glaze is "stretched" on the clay (because it has a higher thermal contraction). When the lines are close together like this it indicates a more serious issue (I have highlighted them with dye). If the effect is intended, it is called "crackle" (but no one would intend this on functional ware). The glaze on the left calculates to a high thermal expansion so the crazing is not a surprise.

Links

Glossary Crazing
Crazed ceramic glazes have a network of cracks. Understanding the causes is the most practical way to solve it. 95% of the time the solution is to adjust the thermal expansion of the glaze.
Materials Ferro Frit 3110
Materials Feldspar
Oxides Al2O3 - Aluminum Oxide, Alumina
Oxides Na2O - Sodium Oxide, Soda
Oxides KNaO - Potassium/Sodium Oxides

By Tony Hansen


Tell Us How to Improve This Page

Or ask a question and we will alter this page to better answer it.

Email Address

Name

Subject

Message


Upload picture


Copyright 2008, 2015, 2017 https://digitalfire.com, All Rights Reserved