Monthly Tech-Tip from Tony Hansen SignUp

No tracking! No ads!

200 mesh | 325 mesh | 3D Design | 3D Printer | 3D Printing Clay | 3D Slicer | 3D-Printing | Abrasion Ceramics | Acidic Oxides | Agglomeration | Alkali | Alkaline Earths | 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 | 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 Foresight | Digitalfire Insight | Digitalfire Reference Library | Dimpled glaze | Dip Glazing | Dipping Glaze | Dishwasher Safe | 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 | Ink Jet Printing | Inside-only Glazing | Insight-Live | 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 | Mole% | Monocottura | Mosaic Tile | Mottled | Mullite Crystals | Native Clay | Non Oxide Ceramics | Oil-spot glaze | Once fire glazing | Opacifier | Opacity | Ovenware | Overglaze | | 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 | 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 | Sieve | Sieve Shaker | Silica:Alumina Ratio | 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 in Ceramics | Water Smoking | Water Solubility | Wedging | Whiteware | Wood Ash Glaze | Wood Firing | Zero3 | Zero4 | Zeta Potential

Oxidation Firing

In ceramics, this term is most often used to refer to kilns firing with an atmosphere having available oxygen to react with glaze and body surfaces during firing

Key phrases linking here: oxidation firing - Learn more

Details

A firing where the atmosphere inside the kiln has sufficient supplies of oxygen to react with the glaze and clay body surfaces (and thus produce the colors characteristic of this). Electric kilns are synonymous with oxidation firing. However these kilns lack the air flow of their gas counterparts. Stagnant air inside can be saturated with carbon and other products of decomposition from bodies and glazes and these can use up oxygen in the chamber. This produces more neutral atmosphere than intended or realized (especially if glaze and body materials have high LOIs). Directly-connected kiln vents improve this situation but still do not approach the ventilation in gas kilns.

Oxidation glazes are typically more brightly colored than reduction ones, especially at lower temperatures. Iron (Fe2O3) is not a flux in oxidation kilns. Generally, potters and hobbyists who employ reduction in their kilns, fire at higher temperatures.

Industries that use periodic and tunnel kilns for fast-fire typically fire in oxidation or neutral atmospheres.

Related Information

The same glaze in reduction (left) and oxidation at cone 10

Tap picture for full size and resolution

It is not just iron oxide that changes character from oxidation to reduction. Of course, cobalt can fire to a bright blue in oxidation also, but this will only happen if its host glaze is glossy and transparent. In this case the shift to reduction has altered the character of the glaze enough so that its matte character subdues the blue.

How reduction firing can affect glaze color

Tap picture for full size and resolution

An example of how the same dolomite cobalt blue glaze fires much darker in oxidation than reduction. But the surface character is the same. A different base glaze having the same colorant might fire much more similar. The percentage of colorant can also be a factor in how similar they will appear. The identity of the colorant is important, some are less prone to differences in kiln atmosphere. Color interactions are also a factor. The rule? There is none, it depends on the chemistry of the host glaze, which color and how much there is.

Gleason ball clay fired test bars from cone 7-11 oxidation and cone 10 reduction

Tap picture for full size and resolution

The oxidation bars (lower) are typical of most ball clays. They burn off-white and darken slightly in color as they approach maturity (above cone 10). Ball clays are fairly refractory, often as much more more than common fireclays. Ball clays almost always have some soluble salts and these reveal themselves in reduction firing (top bar).

Cone 5 reduction mug (left) and cone 6 oxidation mug (right)

Tap picture for full size and resolution

These are made from Plainsman M340 and have transparent glazes. Notice the grey color of reduction vs. the yellowish of oxidation.

Difference between oxidation and reduction! GR10-C matte on Plainsman H443

Tap picture for full size and resolution

Same body, same glaze. Left is cone 10 oxidation, right is cone 10 reduction. What a difference! This is a Ravenscrag-Slip-based recipe on a high-fire iron stoneware. In reduction, the iron oxide in the body and glaze darkens (especially the body) and melts much more. The behavior of the tin oxide opacifier is also much different (having very little opacifying effect in reduction).

Links

Glossary Reduction Firing
A method of firing stoneware where the kiln air intakes and burners are set to restrict or eliminate oxygen in the kiln such that metallic oxides convert to their reduced metallic state.
Glossary LOI
Loss on Ignition is a number that appears on the data sheets of ceramic materials. It refers to the amount of weight the material loses as it decomposes to release water vapor and various gases during firing.
Typecodes Oxidation Firing
Articles Electric Hobby Kilns: What You Need to Know
Electric hobby kilns are certainly not up to the quality and capability of small industrial electric kilns, being aware of the limitations and keeping them in good repair is very important.
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