3D Design | 3D Printer | 3D Slicer | 3D-Printed Clay | 3D-Printing | Abrasion Ceramics | Acidic Oxides | Agglomeration | Alkali | Alkaline Earths | Amorphous | Apparent porosity | Ball milling | Bamboo Glaze | Base Glaze | Base-Coat Dipping Glaze | Basic Oxides | Batch Recipe | Bisque | Bit Image | Black Coring | Bleeding colors | Blisters | Bloating | Blunging | Bone China | Borate | Boron Blue | Boron Frit | Borosilicate | Breaking Glaze | Brushing Glaze | Buff stoneware | Calcination | Calculated Thermal Expansion | Candling | Carbon Burnout | Carbon trap glazes | CAS Numbers | Casting-Jiggering | Celadon Glaze | Ceramic | Ceramic Binder | Ceramic Decals | Ceramic Glaze | 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 | Co-efficient of Thermal Expansion | Code Numbering | Coil pottery | Colloid | Colorant | Cone plaque | Cones | Copper Red | Cordierite Ceramics | Crackle glaze | Crawling | Crazing | Cristobalite | Cristobalite Inversion | Crucible | Crystalline glazes | Crystallization | Cuerda Seca | Cutlery Marking | De-Airing Pugmill | Decomposition | Deflocculation | Deoxylidration | 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 Stains | Engobe | Eutectic | Fast Fire Glazes | Fat Glaze | Feldspar Glazes | 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 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 | Insight-Live | Interface | Iron Red Glaze | Jasper Ware | Jiggering | Kaki | Kiln Controller | Kiln Firing | Kiln fumes | Kiln venting system | Kiln Wash | Kovar Metal | Laminations | Leaching | Lead in Ceramic Glazes | Leather hard | Lime Popping | Limit Formula | 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 | Micro Organisms | Microwave Safe | 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 | PCE | Permeability | Phase change | Phase Diagram | Phase Separation | Physical Testing | Pinholing | Plainsman Clays | Plaster Bat | Plaster table | Plasticine | Plasticity | Plucking | Porcelain | Porcelaineous Stoneware | Pour Glazing | | Primary Clay | Primitive Firing | Production Setup | Propane | Propeller Mixer | Pyroceramics | Pyroceramics | Quartz Inversion | Raku | Reactive Glazes | Reduction Firing | Reduction Speckle | Refractory | Refractory Ceramic Coatings | Representative Sample | Respirable Crystalline Silica | Rheology | Rutile Glaze | Salt firing | Sanitary ware | Sculpture | Secondary Clay | Shino Glazes | Shivering | Sieve | Silica:Alumina Ratio (SiO2:Al2O3) | Silk screen printing | Sintering | Slaking | Slip Casting | Slip Trailing | 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 | Tony Hansen | Toxicity | Tranlucency | Translucency | Transparent Glazes | Triaxial Glaze Blending | Ultimate Particles | Underglaze | Unity Formula | Upwork | Viscosity | Vitrification | Volatiles | Warping | Water in Ceramics | Water Smoking | Water Solubility | Wedging | Whiteware | Wood Ash Glaze | Wood Firing | Zero3 | Zeta Potential

Precipitation

Crystals or crystalline particles will often form over time in ceramic glaze slurries that contain slightly soluble materials.

Details

If a glaze slurry contains soluble or partially soluble raw materials or is made using hard water, then solids can precipitate over time forming hard lumps, crystals or a scum. At a minimum the solubility of many materials is enough to stain the water in a slurry (seen on the top after the powder has settled).

It seems logical that ceramic powdered materials, being ground up rock or glass (in the case of frits) would not be soluble. But this is not the case. Solubility is often a matter of chemistry. Certain frit chemistries, for example, are much more vulnerable to dissolution. This is because frits often need to push the boundaries of stability (therefore solubility) to deliver the desired chemistry (e.g. those lacking alumina). Frit production is not always precise, variations can lead to instability. Stains are also subject to solubility (for this reason some are acid washed).

Solubility of materials is often a simple product of increased surface area. For example, the solubility of feldspar or nepheline syenite rock is very low, but when ground into a powder its surface area is multiplied thousands or millions of times. This is enough to create noticeable solubility. Other materials are known to be contaminated by soluble salts. Gerstley borate, for example, gels glaze slurries, so obviously it is releasing ions into the suspension (its constituent minerals are also less stable than most other common ceramic materials). Ball clays likewise release scum as they dry (solubles are sourced from contaminants that get ground up with the clay itself, these are carried to the surface and precipitate there as brown scum as the water evaporates away). Manufactured materials like barium carbonate and lithium carbonate are partially soluble (this is just what they are).

Precipitation is not just a product of over saturation that occurs over time. It can also be a product of the interaction of various ions to be found in solution (which may well want to interact). Often it may appear that a particular material is guilty of precipitating in a specific glaze, however that same material may appear in another recipe where no precipitation occurs.

You can minimize precipitation and solubility in glazes by storing them in a cool place. And by making smaller batches and cycling them more often. Solubility of stains can affect the fired product (producing cloudiness on the surface of fired ware). In such cases it may be necessary to wash your stains before use (in vinegar for example).

Related Information

Soluble ingredients in glazes always precipitate as angular crystals. Right?

Wrong. These tiny spheres (actually they are not so tiny) form over time as a precipitate in a glaze having a high concentration of a boron frit and mixed in hard water. This may be an example of how interactions can affect the degree to which materials dissolve in water (in this case the electrolyte in the water could be a trigger). These are likely ooids.

Here is what happens if you do not sieve your glazes when needed

This is a cone 6 transparent base glaze. It contains frit, silica, kaolin, wollastonite. Almost all glazes have materials that are slightly soluble and over time these can form scale on the sides of the bucket or even precipitate particles into the slurry. The defects here are those scales. Before dipping a production piece in any glaze that has been in storage it is a good idea to assess it first to see if it needs to be sieved.

Add 5% calcium carbonate to a tenmoku. What happens?

In the glaze on the left (90% Ravenscrag Slip and 10% iron oxide) the iron is saturating the melt crystallizing out during cooling. GR10-K1, on the right, is the same glaze but with 5% added calcium carbonate. This addition is enough to keep most of the iron in solution through cooling, so it contributes to the super-gloss deep tenmoku effect instead of precipitating out.

Precipitated crystals from a glaze having 60% lead bisilicate frit

It also contains less than 10% borax frit and some Cornwall stone.

Precipitate can forms in fritted glazes, remember to screen it

Potters often store glazes for long periods so tiny spherical precipitate particles can form. These were found in a months-old bucket of G2926B (M370 clear) cone 6 clear glaze (about 2 gallons). These can appear over time, depending on factors like temperature, electrolytes in your water or solubility in the materials (likely, the frit is slightly soluble). The glaze slurry should be screened periodically (or immediately if you note the particles when glazing a piece). This is an 80 mesh screen. Note the brush, using one of these gets the glaze through the screen much quicker than using a rubber spatula.

Are frits partially soluble? Yes, many are.

These 1 mm-sized crystals were found precipitated in a couple of gallons of glaze containing 85% Ferro Frit 3195. They are cubical, hard and insoluble. Why and how to do they form? Many frits are slightly partially soluble and the degree to which they are are related to the length of time the glaze is in storage, the temperature, the electrolytes and solubles in the water and interactions with other material particles present. The solute then interacts with other materials particles to form insoluble species that crystallize and precipitate out as you see here. These crystals can be a wide range of shapes and sizes and come from leaded and unleaded frits.

A glaze slurry precipitates flakes

These flakes have been screened from a highly-fritted boron glaze mixed using hard water and stored for a year. They formed as a film across the top of the settled surface and on the walls of the bucket. Frits are stoichiometric, they should not dissollve, but they do. Perhaps this is evidence that frit makers are unable to precisely control production parameters.

Links

URLs https://en.wikipedia.org/wiki/Precipitation_(chemistry)
Precipitation at Wikipedia
URLs https://en.wikipedia.org/wiki/Ooid
Ooids in Glazes
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.

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