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 | AI in Ceramics | 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 | | 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 | 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 | 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

Borate

Borate glazes, those fluxed with the oxide B2O3, are the most common type used in ceramic industry and hobby for low and medium temperatures.

Key phrases linking here: borate, boron - Learn more

Details

The term 'boron' refers to the oxide B2O3. 'Borate materials' thus contain B2O3, they source it to glass-building during melting in the kiln. Boron is actually the potter's friend (because of his electronic-controller-equipped kiln) while as the same time it can be a scourge in industry (because they are forced to fast fire), we will see how that is.

Boron is a flexible oxide because it is a glass (can substitute for SiO2, with some loss in hardness of course, and combines readily with bases and colors). It is also a non-toxic flux with a low thermal expansion. Boron is not a common mineral on planet earth. Most of the world's reserves are in Turkey, but also in the US, Chile, Russia. Insoluble boron is sourced by frits, Colemanite, Ulexite and Gerstley Borate (actually Gerstley Borate gels the slurry so it is partially soluble).

Almost all low temperature glazes owe their existence to boron-sourcing materials. Other than lead (which is superior in almost every way), no other commonly available flux will melt a glaze at cone 04-06. But boron-containing frits and raw materials will. Thousands of different boron frits are available around the world (containing from 1 to 50% or more B2O3), people and companies often use them without a second thought to the magic of the boron in them. It is common for glazes to contain up to 90% frit, adding just 10% kaolin for the slurry properties they need in manufacturing. However many low fire glazes can be made using much less frit and adding materials typical to higher temperature glazes (like feldspar, silica, ball clay). Gerstley Borate has long been used in North America as a source of B2O3, it actually contains a much higher percentage than any commonly available frit. However only potters are willing to endure the process issues it introduces. Boron low fire glazes are certainly not without their problems, these include clouding (from micro-bubbles), crystallization (boron blue), dimples, pinholes, etc. However these can generally be solved by firing curve alterations and changing materials or chemical balance. Because boron has such a low thermal expansion its glazes are quite adjustable in thermal expansion (e.g. by lowering and raising Na2O). The fast fire techniques that increasing numbers of manufacturers use in recent years are not practical with low fire boron glazes (they melt to early and have too many defects), but potters can adapt. The big benefit is that brilliant colors are so much easier to produce. In fact, by adding a little frit to their bodies and being patient and creative with firing curves (using an electronic controller), low temperature potters can produce stoneware!

Many people that have made and used middle temperature glazes (cone 4-8) are unaware that B2O3 is the key fluxing oxide (in most glazes) and that it makes melting possible at cone 6. No combination of common raw flux-sourcing materials like feldspar, nepheline syenite, calcium carbonate, dolomite and talc mixed with silica and kaolin will melt nearly enough at cone 6 to produce a functional glossy glaze. At first it might seem that since Li2O and ZnO are super-fluxes we could simply add a little of them (e.g. 5%) to high temperature glazes (already fluxed employing the standard oxides Na2O, K2O, CaO and MgO from the above materials). While that can actually work and be tolerated in some circumstances, their source materials are not only expensive but can be troublesome in the glaze suspension, producing bubbles, flocculating the slurry and producing cracks on drying (which lead to crawling). In the firing glaze they can volatilize and can dramatically affect the colouring mechanism of stains and metal oxides. In the fired glaze they can introduce leaching issues. So, not surprisingly, the entire ceramic and enamel industry have traditionally relied on the flux B2O3 (boron) to make good base glazes at low and medium temperatures. However larger scale manufacturers that fast fire (and fast cool) must also minimize B2O3 content (to avoid its early melting and glaze defects that produces in the absense of soaking and slow cooling). They are thus forced to find ways to use more ZnO and Li2O. But potters with their electronically controlled kilns and more patience are once again the winners. They have the time to soak firings are temperature, cool them a little and soak again, and control temperature fall as far as they want. These factors can transform boron glazes into something industry could not produce.

Related Information

Your boron glaze might melt alot earlier than you think

Tap picture for full size and resolution

The porcelain mug on the left is fired to cone 6 with G2926B clear glossy glaze. This recipe only contains 25% boron frit (0.33 molar of B2O3). Yet the mug on the right (the same clay and glaze) is only fired to cone 02 yet the same glaze is already well melted! What does this mean? Industry avoids high boron glazes (they consider 0.33 to be high boron) because this early melting behavior means gases cannot clear before the glaze starts to melt (causing surface defects). For this reason, fast fire glazes melt much later. Yet many middle temperature reactive glazes in use by potters have double the amount of B2O3 that this glaze has!

In pursuit of a reactive cone 6 base that I can live with

Tap picture for full size and resolution

These GLFL tests and GBMF tests for melt-flow compare 6 unconventionally fluxed glazes with a traditional cone 6 moderately boron fluxed (+soda/calcia/magnesia) base (far left Plainsman G2926B). The objective is to achieve higher melt fluidity for a more brilliant surface and for more reactive response with colorant and variegator additions (with awareness of downsides of this). Classified by most active fluxes they are:
G3814 - Moderate zinc, no boron
G2938 - High-soda+lithia+strontium
G3808 - High boron+soda (Gerstley Borate based)
G3808A - 3808 chemistry sourced from frits
G3813 - Boron+zinc+lithia
G3806B - Soda+zinc+strontium+boron (mixed oxide effect)
This series of tests was done to choose a recipe, that while more fluid, will have a minimum of the problems associated with such (e.g. crazing, blistering, low run volatility, susceptibility to leaching). As a final step the recipe will be adjusted as needed. We eventually evolved the G3806B, after many iterations settled on G3806E or G3806F as best for now.

Let me count the reasons this glossy white cone 6 glaze is pinholing

Tap picture for full size and resolution

First, the layer is very thick. Second, the body was only bisque fired to cone 06 and it is a raw brown burning stoneware with lots of coarser particles that generate gases as they are heated. Third, the glaze contains zircopax, it stiffens the melt and makes it less able to heal disruptions in the surface. Fourth, the glaze is high in B2O3, so it starts melting early (around 1450F) and seals the surface so the gases must bubble up through. Fifth, the firing was soaked at the end rather than dropping the temperature a little first (e.g. 100F) and soaking there instead.

Can a decal firing melt a glaze? Yes!

Tap picture for full size and resolution

Typical zero-boron high temperature glazes will not soften in a 1500F decal firing. But low temperature glazes will (especially those high in boron). Even middle temperature ones can soften. G3806C, for example, is reactive and fluid, it certainly will. Even G2926B, which has high Al2O3 and SiO2, has enough boron to soften and sometimes create tiny pits. In serious cases they can bubble like the mug on the right. Why? Steam. It was in use and had been absorbing water in the months since it was first glaze fired at cone 03. The one on the left was not used, but it did have some time to absorb water from the air, it is showing tiny pits in the surface. Even if moisture is not present, low fire bodies especially may still have some gases of decomposition to affect the glaze. One more thing: Fire the decals at the recommended temperature, often cone 022.

Slow cooling vs. fast cooling on a cone 6 transparent glaze

Tap picture for full size and resolution

These are the inside uppers on two mugs made from the same clay with the same clear glaze. The one on the left was fired in a large electric kiln full of ware (thus it cooled relatively slowly). The one on the right was in a test kiln and was cooled rapidly. This glaze contains 40% Ferro Frit 3134 so there is plenty of boron and plenty of calica to grow the borosilicate crystals that cause the cloudiness in the glass. But in the faster cooling kiln they do not have time to grow.

Can a cone 6 functional glaze having only whiting and feldspar melt enough?

Tap picture for full size and resolution

This flow test compares the base and base-plus-iron version of a popular CM recipe called "Tenmoku Cone 6" (20% whiting, 35% Custer feldspar, 15% Ball Clay and 30% silica, 10% iron oxide). Although iron is not a flux in oxidation, it appears to be doing exactly that here (that flow is just bubbling its way down the runway, the white one also fires to a glassy surface on ware). It looks melted in the tray on the right but notice how easily it is scratching on the tile (lower left). This demonstrates that looks can be deceiving. Cone 6 functional glazes always have some percentage of a power flux (like boron, lithia, zinc), otherwise they just do not melt into a hard glass. Maybe a glaze looks melted, but it has poor durability.

Links

Materials Borax Pentahydrate
Materials MOK 3 Borax frit
Materials Gerstley Borate
Gerstley Borate was a natural source of boron for ceramic glazes. It was plastic and melted clear at 1750F. Now we need to replace it. How?
Materials Ulexite
A natural source of boron, it melts at a very low temperature to a clear glass.
Glossary Borosilicate
Glossary Boron Frit
Most ceramic glazes contain B2O3 as the main melter. This oxide is supplied by great variety of frits, thousands of which are available around the world.
Glossary Firing Schedule
Designing a good kiln firing schedule for your ware is a very important, and often overlooked factor for obtained successful firings.
Minerals Borate Minerals
The major borate minerals are Colemanite and Ulexite. The geology required for borates is found in v
Media Convert a Cone 10 Glaze to Cone 6 Using Desktop Insight
Learn the chemistry differences between cone 10 and 6 glazes and how to make a glaze melt at a lower temperature without introducing other problems like crazing.
URLs http://www.ceramicindustry.com/articles/borates-a-new-flux-for-glossy-glazes
Formulating borate glazes to premit refire without loss in gloss
Oxides B2O3 - Boric Oxide
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