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 | 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 | | 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

Kiln Wash

A high-melting powder applied to kiln shelves to prevent ware from sticking to the shelf during firing. It is also used as a parting agent for to keep elements of fired ware from sticking to each other.

Key phrases linking here: kiln wash - Learn more

Details

A refractory powder that can be mixed with water (and gum solution) and painted on kiln shelves to prevent ware and accidental glaze drips from sticking. Porcelain clays, for example, melt enough during firing that they tend to stick onto the kiln shelf. But with a good wash there are no problems. Certain clays contain soluble salts which fire to a glaze-like sheen, these also tend to stick ware to shelves.

When a shelf is properly protected by kiln wash, pure molten glaze can run onto it during firing and simply be lifted off when the kiln is unloaded. If the kiln wash works really well, lifting it off will only take upper layers of the refractory wash powder, leaving some still on the shelf. Wash should be reapplied to areas when it has flaked off or is getting thin. It is thus important for the kiln wash powder to be as refractory as possible. Non-refractory washes harden into flakes that stick to the bottoms of ware. A very high percentage of calcined alumina is theoretically best. Even better, zircon (these powders are very fine, they create a good slurry).

Common recipes contain high percentages of kaolin (50:50 kaolin:silica is common). This percentage is creating a clay-body-like material (also having plenty of drying shrinkage). A small amount of feldspar can be found in some recipes. This is strange, perhaps it is used to de-powder the fired layer. Sometimes kiln washes are deflocculated. This is also not necessary, it makes a brushing wash that already dries much too fast dry even faster.

Application to refractory shelves and furniture is generally done by painting. If using the 50:50 kaolin:silica recipe it is best to minimize water so it stays in suspension (we have found good results using 50:50 water:powder). Given the above-mentioned materials, a simple slurry of water and powder will create a white-wash style slurry that will dry on-contact to porous refractory surfaces, that can make it difficult to achieve an even-thickness and smooth application. One solution is to employ CMC Gum in a manner similar to making brushing glazes. The gum will slow drying speed, making it flow and apply like a paint. The gum will also prevent cracking during drying, enabling lay-down of multiple layers if needed. Additionally, the gum makes it possible to minimize raw clay content, reducing shrinkage (e.g. switching some of the raw kaolin in the mix to flat-particled calcined kaolin).

Good quality kiln wash can be used to line crucibles so that molten materials will shed off or can be removed as an ingot after the kiln cools.

Related Information

Flaking kiln wash on a silicon carbide kiln shelf

Tap picture for full size and resolution

This is a 50:50 kaolin:silica wash. While economical, this is not an ideal recipe. It gets too hard and shrinks too much during drying and firing. It is better to use a recipe that remains somewhat powdery to the touch. Pure calcined alumina with a little calcined kaolin (about 10%) gives almost zero shrinkage. Add more kaolin if it fires too powdery or less if fires too hard. Add 1% CMC gum to produce a very paintable material (it will take some time to dry).

A running glaze has stuck to a kiln shelf. Kiln wash saves the day!

Tap picture for full size and resolution

This is a zircon-based kiln wash. Even though it paints on in a thin layer, there is no problem releasing the very runny glaze from the shelf.

Kiln wash that really works. How?

Tap picture for full size and resolution
Two kiln shelves, the wash on one is even and perfect, the other is flaking and falling off

The shelf on the right in the traditional kaolin:silica kiln wash. Flaking constantly. Sticking on the feet of ware. A real aggravation. The one on the left is L4001, it is perfectly even. Yet thin. Much more refractory so it has not hardened or become brittle. Or cracked. And it paints on beautifully. The secret? Zircon. Zircopax, to be precise. Zircopax is among the most refractory materials in ceramics. We mixed it with some calcined, rather than raw kaolin. That greatly reduces drying and firing shrinkage and helps densify and stabilize the coverage (by its flat particle shape). Laguna gum solution was added to harden the dry layer and slow down the drying (their gum solution has a higher percentage of CMC than achievable using common mixing methods). Click the link below to get the recipe.

The foot ring on the left is plucking, the right one is not. Why?

Tap picture for full size and resolution

These are translucent porcelains, they are vitreous. The firing is to cone 10. The one on the left is a cone 6 body, and, while it survives to cone 10 it does warp. But more important, it is much more vitreous (more melted). The plucking problem makes it quite difficult to get a good foot ring. The other, which has only slight plucking, is also quite vitreous (high in feldspar). The plucking problem on both can be solved by simply using a better kiln wash. What is better? More refractory, and therefore having a powdery, non-stick surface. Spend more money on your kiln wash, base it on calcined alumina or zircon.

Even with good kiln wash plucking can sometimes occur

Tap picture for full size and resolution

These were left by ware made from a cone 6 highly vitreous translucent porcelain. For that type of clay it would be advisable to set ware on a thin layer of silica sand or granular alumina.

Links

Glossary Water Solubility
The water solubility of ceramic materials is an important consideration to their usability in the process. Glazes are suspensions of insert powders, solubles present problems to this system.
Glossary Plucking
A firing issue in ceramics where the foot rings of vitreous ware stick to the kiln shelf. Removing them leaves sharp fragments glued to the shelf.
URLs https://insight-live.com/insight/share.php?z=DDBJSBWmiM
Refractory Alumina body, Zircon Kiln wash recipes
URLs https://insight-live.com/insight/share.php?z=K5hHzDs2Kr
Plainsman Super Kiln Wash
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