Monthly Tech-Tip from Tony Hansen SignUp

No tracking! No ads!

200 mesh | 325 mesh | 3D Design | 3D Modeling | 3D Printer | 3D Printing Clay | 3D Slicer | 3D-Printing | Abrasion Ceramics | Acidic Oxides | Agglomeration | AI in Ceramics | Alkali | Alkaline Earths | All-in-one case mold | Amorphous | Apparent porosity | Artware | Ball milling | Bamboo Glaze | Base Glaze | Base-Coat Dipping Glaze | Basic Oxides | Batch Recipe | Bisque | Bit Image | Black Core | Bleeding of colors | Blender Mixing | Blunging | Body Bloating | Body glaze Interface | Body Warping | 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 | Catch Glaze | Celadon Glaze | Ceramic | Ceramic Binder | Ceramic Decals | Ceramic Glaze | Ceramic Glaze Defects | Ceramic Ink | Ceramic Material | Ceramic Oxide | Ceramic Slip | Ceramic Stain | Ceramic Tile | Ceramic Transfer | Ceramics | Characterization | Chemical Analysis | Chromaticity | Clay | Clay body | Clay Body Porosity | Clay Stiffness | Clays for Ovens and Heaters | Co-efficient of Thermal Expansion | Code Numbering | Coil pottery | Colloid | Colorant | Commercial hobby brushing glazes | Cone 1 | Cone 5 | Cone 6 | Cone plaque | Copper Red | Cordierite Ceramics | Crackle glaze | Cristobalite | Cristobalite Inversion | Crucible | Crystalline glazes | Crystallization | Cuerda Seca | Cutlery Marking | Decomposition | Deflocculation | Deoxylidration | Differential thermal analysis | Digitalfire API | Digitalfire Foresight | Digitalfire Insight | Digitalfire Insight-Live | Digitalfire Reference Library | Digitalfire Taxonomy | Dimpled glaze | Dip Glazing | Dipping Glaze | Dishwasher Safe | Displacer | 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 Blisters | Glaze Bubbles | Glaze Chemistry | Glaze Compression | Glaze Crawling | Glaze Crazing | Glaze Durability | Glaze fit | Glaze Gelling | Glaze laydown | Glaze Layering | Glaze Mixing | Glaze Recipes | Glaze shivering | Glaze Shrinkage | Glaze thickness | Globally Harmonized Data Sheets | Glossy Glaze | Green Strength | Grog | Gunmetal glaze | High Temperature Glaze | Hot Pressing | Incised decoration | Industrial clay body | Infill and Support | Ink Jet Printing | Inside-only Glazing | Iron Red Glaze | Jasper Ware | Jiggering | Kaki | Kiln Controller | Kiln Firing | Kiln fumes | Kiln venting system | Kiln Wash | Kneading clay | Kovar Metal | Laminations | Leaching | Lead in Ceramic Glazes | Leather hard | 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 | Mold Natches | 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 | Particle Sizes | PCE | Permeability | Phase Diagram | Phase Separation | Physical Testing | Pinholing | Plainsman Clays | Plaster Bat | Plaster table | Plasticine | Plasticity | Plucking | Porcelain | Porcelaineous Stoneware | Pour Glazing | Pour Spout | 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 | Restaurant Ware | Rheology | Rutile Blue Glazes | Salt firing | Sanitary ware | Sculpture | Secondary Clay | Shino Glazes | Side Rails | Sieve | Sieve Shaker | | 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 | Water Content | Water in Ceramics | Water Smoking | Water Solubility | Wedging | Whiteware | WooCommerce | Wood Ash Glaze | Wood Firing | WordPress | Zero3 | Zero4 | Zeta Potential

Silica:Alumina Ratio

A formula ratio used to evaluate and predict firing properties in ceramic glazes.

Key phrases linking here: silica:alumina ratio - Learn more

Details

The ratio of silicon dioxide to alumina oxide (SiO2:Al2O3 ratio) is often used as an indicator of glaze matteness. A glaze with high alumina thus has a low silica:alumina ratio. This ratio has some value because alumina stiffens the glaze melt (stiffer melts do not smooth out as well on cooling thus creating a fired surface that scatters light). There are obvious limitations to using this indicator since there are other mechanisms and influencers of glaze matteness (e.g. crystallization, firing temperature). Generally, the mechanism of matteness is never purely the alumina:silica ratio. The presence of boron can gloss even a high alumina mix. Of course firing temperature affects gloss (a glossy glaze will be matte if under fired). Firing range is another variable: at low temperatures high temperature fluxing oxides (e.g. CaO, MgO) turn into matting agents (via melt stiffening). In addition, the presence of zinc can cause crystallization and matteness in an otherwise glossy glaze that even has a very high ratio. CaO in large amounts is a matting agent in high and medium temperature glazes (via crystallization). Opacifers will affect matteness.

If you are aware of all the mechanisms and interactions present, there are many cases where you can make use of the SiO2:Al2O3 ratio to some degree to control matteness by adjusting the ratio. The G1214Z recipe is a good example of this. If a glaze is already glossy and the SiO2:Al2O3 ratio is quite low and it is melting well this likely indicates that the glaze has the capacity to accept much more silica to raise, not only the ratio, but improve many other fired properties at the same time (see the example photo linked to this topic).

Related Information

If your glaze can handle more silica and melt just as well then add it!


The cone 6 G1214M glaze on the left melts well. Can it benefit from a silica addition? Yes. The right adds 20% yet still melts as well, covers better, is more glossy, more resistant to leaching, harder and has a lower thermal expansion.

Links

Glossary Matte Glaze
Random material mixes that melt well overwhelmingly want to be glossy, creating a matte glaze that is also functional is not an easy task.
Glossary Dolomite Matte
Dolomite matte glazes have the potential to be very silky and pleasant to the touch, while at the same time being hard, durable and non-crazed (if they are formulated correctly).
Glossary Formula Ratios
The ratios of individual or group oxide molecule numbers are indicators of things like fired gloss, durability, melting temperature, balance, tendency to craze, etc.
Articles G1214Z Cone 6 matte glaze
This glaze was developed using the 1214W glossy as a starting point. This article overviews the types of matte glazes and rationalizes the method used to make this one.
Recipes G1214M - Original Cone 6 Base Glossy Glaze
A recipe developed by Tony Hansen in the 1980s. Its was popular because of the simplicity of the recipe and how well it worked with chrome-tin stains.
By Tony Hansen
Follow me on

Got a Question?

Buy me a coffee and we can talk

 



https://digitalfire.com, All Rights Reserved
Privacy Policy