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A Low Cost Tester of Glaze Melt Fluidity
A One-speed Lab or Studio Slurry Mixer
A Textbook Cone 6 Matte Glaze With Problems
Adjusting Glaze Expansion by Calculation to Solve Shivering
Alberta Slip, 20 Years of Substitution for Albany Slip
An Overview of Ceramic Stains
Are You in Control of Your Production Process?
Are Your Glazes Food Safe or are They Leachable?
Attack on Glass: Corrosion Attack Mechanisms
Ball Milling Glazes, Bodies, Engobes
Binders for Ceramic Bodies
Bringing Out the Big Guns in Craze Control: MgO (G1215U)
Ceramic Glazes Today
Ceramic Material Nomenclature
Ceramic Tile Clay Body Formulation
Changing Our View of Glazes
Chemistry vs. Matrix Blending to Create Glazes from Native Materials
Concentrate on One Good Glaze
Cone 6 Floating Blue Glaze Recipe
Copper Red Glazes
Crazing and Bacteria: Is There a Hazard?
Crazing in Stoneware Glazes: Treating the Causes, Not the Symptoms
Creating a Non-Glaze Ceramic Slip or Engobe
Creating Your Own Budget Glaze
Crystal Glazes: Understanding the Process and Materials
Deflocculants: A Detailed Overview
Demonstrating Glaze Fit Issues to Students
Diagnosing a Casting Problem at a Sanitaryware Plant
Drying Ceramics Without Cracks
Duplicating Albany Slip
Duplicating AP Green Fireclay
Electric Hobby Kilns: What You Need to Know
Fighting the Glaze Dragon
Firing Clay Test Bars
Firing: What Happens to Ceramic Ware in a Firing Kiln
First You See It Then You Don't: Raku Glaze Stability
Fixing a glaze that does not stay in suspension
Formulating a body using clays native to your area
Formulating a Clear Glaze Compatible with Chrome-Tin Stains
Formulating a Porcelain
Formulating Ash and Native-Material Glazes
G1214M Cone 5-7 20x5 Glossy Base Glaze
G1214W Cone 6 Transparent Base Glaze
G1214Z Cone 6 Matte Base Glaze
G1916M Cone 06-04 Base Glaze
G1947U/G2571A Cone 10/10R Base Matte/Glossy Glazes
Getting the Glaze Color You Want: Working With Stains
Glaze and Body Pigments and Stains in the Ceramic Tile Industry
Glaze Chemistry Basics - Formula, Analysis, Mole%, Unity
Glaze chemistry using a frit of approximate analysis
Glaze Recipes: Formulate Your Own Instead
Glaze Types, Formulation and Application in the Tile Industry
Having Your Glaze Tested for Toxic Metal Release
High Gloss Glazes
How a Material Chemical Analysis is Done
How desktop INSIGHT Deals With Unity, LOI and Formula Weight
How to Find and Test Your Own Native Clays
How to Liner-Glaze a Mug
I've Always Done It This Way!
Inkjet Decoration of Ceramic Tiles
Is Your Fired Ware Safe?
Leaching Cone 6 Glaze Case Study
Limit Formulas and Target Formulas
Low Budget Testing of the Raw and Fired Properties of a Glaze
Low Fire White Talc Casting Body Recipe
Make Your Own Ball Mill Stand
Making Glaze Testing Cones
Monoporosa or Single Fired Wall Tiles
Organic Matter in Clays: Detailed Overview
Outdoor Weather Resistant Ceramics
Painting Glazes Rather Than Dipping or Spraying
Particle Size Distribution of Ceramic Powders
Porcelain Tile, Vitrified or Granito Tile
Rationalizing Conflicting Opinions About Plasticity
Ravenscrag Slip is Born
Recylcing Scrap Clay
Reducing the Firing Temperature of a Glaze From Cone 10 to 6

Single Fire Glazing
Soluble Salts in Minerals: Detailed Overview
Some Keys to Dealing With Firing Cracks
Stoneware Casting Body Recipes
Substituting Cornwall Stone
Super-Refined Terra Sigillata
The Chemistry, Physics and Manufacturing of Glaze Frits
The Effect of Glaze Fit on Fired Ware Strength
The Four Levels on Which to View Ceramic Glazes
The Majolica Earthenware Process
The Potter's Prayer
The Right Chemistry for a Cone 6 MgO Matte
The Trials of Being the Only Technical Person in the Club
The Whining Stops Here: A Realistic Look at Clay Bodies
Those Unlabelled Bags and Buckets
Tiles and Mosaics for Potters
Toxicity of Firebricks Used in Ovens
Trafficking in Glaze Recipes
Understanding Ceramic Materials
Understanding Ceramic Oxides
Understanding Glaze Slurry Properties
Understanding the Deflocculation Process in Slip Casting
Understanding the Terra Cotta Slip Casting Recipes In North America
Understanding Thermal Expansion in Ceramic Glazes
Unwanted Crystallization in a Cone 6 Glaze
Volcanic Ash
What Determines a Glaze's Firing Temperature?
What is a Mole, Checking Out the Mole
What is the Glaze Dragon?
Where do I start in understanding glazes?
Why Textbook Glazes Are So Difficult

Simple Physical Testing of Clays

Description

Learn to test your clay bodies and clay materials and record the results in an organized way, understanding the purpose of each test and how to relate its results to changes that need to be made in process, recipe and materials.

Article

If you have been working with glazes and glaze chemistry for some time, you may have developed a mindset that is too narrow when it comes to dealing with clay body formulation. Clay bodies are much more of an adventure in the mineralogy and physical properties of the materials. When glazes melt everything usually goes into solution in the melt, but the vitrification process of a clay is different. The differences in mineralogy, particle size, firing history, body preparation, and ware forming methods all influence the final fired product. Simple tests can indicate plasticity, absorption and shrinkage over a range of temperatures, its water content, density, dry shrinkage, loss on ignition, soluble salts content, drying performance, glaze-over behavior and dry strength.

Lab testing a clay for its physical properties
It only takes a few minutes to make these. But you would be amazed at how much information they can give you about a clay! These are SHAB test bars, an LDW test for water content and a DFAC test disk about to be put into a drier. The SHAB bars shrink during drying and firing, the length is measured at each stage. The LDW sample is weighed wet, dry and fired. The tin can prevents the inner portion of the DFAC disk from drying and this sets up stresses that cause it to crack. The nature of the cracking pattern and its magnitude are recorded as a Drying Factor. The numbers from all of these measurements are recorded in my account at Insight-live. It can present a complete physical properties report that calculates things like drying shrinkage, firing shrinkage, water content and LOI (from the measured values).

Consider these three simple test that we like most for clay bodies: The SHAB test, LDW test and DFAC test. While these are easy to make it does take a few weeks to bring them through all the stages of the process (of course we are running these tests on dozens of clays at any given time and so firing is done in batches).

This subject reveals an interesting comparison between potters and industrial technicians. On one hand, the potter judges a body by how it feels in his hands, how it bends, stretches, pulls, how it behaves on the wheel, how it trims, how it dries, how it reacts visually with his glazes and fires in his kiln. He/she adjusts procedures, recipes and materials to compensate for perceived changes. On the other hand, a ceramic engineer may have never hand-made a piece of ceramic in his life or even kneaded a piece of clay. As a result, he/she may not fully appreciate what plasticity is, for example, viewing it merely in terms of how a clay reacts in machines. To him, dried and fired properties exist as numbers produced by test equipment.

Traditionally potters often had excellent all-around knowledge and intuitive abilities at evaluating clay bodies. Many potter's textbooks today are highly insightful and helpful. Yet there is no denying the value of good physical properties testing and the concrete it produces. The ideal is probably a situation somewhere in between these two extremes. Many body properties are immediately evident in the hands of an experienced potter and not quickly shown by instruments. Likewise, differences shown by physical testing can explain strange behaviour in the process or kiln.

Many large manufacturers in the ceramic industry do not have a standard testing and quality control program in place. It is common to rely completely on suppliers and their tech support. Trouble-shooting manuals they supply speak the language of production-line workers with simple "if this happens do that" style instructions. What about people and companies who want to understand the why questions, become more independent? As noted, setting up a test program to accumulate some data is a good start.

Testing Categories:

Universal Standards

An example is the 50-volume Annual Book of worldwide ASTM Standards (American Society for Testing and Materials). One of the volumes deals with refractories, glaze, and ceramic materials. The books are well organized and describe all test procedures in great detail. Just reference a test by number and you convey all details about how you achieve your results. However these are not for the faint-of-heart. And they are not for people without the lab equipment called for.

Industry Specific Standards

Individual industries like construction, ferrous metals and electrical porcelain have outlined standard testing guidelines more specific to their needs, for example, ANSI (American National Standards Institute). Companies publish data sheets and advertising material in a format that voluntarily recognizes these standards.

Customer Required

Customers sometimes require manufacturers to document product quality and compliance (e.g. ISO 9000 which requires documentation on how tests are done, tolerances, noncompliance procedures, procedure change mechanisms, test equipment calibration schedules, proof of certification, etc). Unfortunately the emphasis of all of this is on documentation and paper, not understanding the physics of the materials.

Internal

Many tests are internal to a company, intended to solve problems, maintain properties critical to production efficiency and cost, control reject rates, etc. In this situation, one is free to formulate any method that seems best for the circumstances. Technicians generally have to make do with what is available, so standard methods are usually adjusted. This is not necessarily bad. Simple tests are sometimes most revealing and practical.

Compiling test bar shrinkage and weights for Insight-live
A batch of fired test bars, organized by temperature, have already been weighed (the weight is written on the side of each bar). Now they will be measured and the SHAB test data (shrinkage/absorption) entered into each recipe record (in an account at insight-live.com). From this data Insight-live can calculate fired shrinkage and fired porosity, enabling you to compare the degree of vitrification of different materials and bodies. This is especially good for quality control purposes.

Getting Started with Internal Testing

We used to have a bunch of information on setting up tests here, but now it seems simpler to just recommend starting with one of the tests built in to Insight-Live. It predefines many tests and the ones of interest to us here are the SHAB test (Shrinkage, Absorption), DFAC test (Drying Factor), SOLU test (Solubles) and LDW test (LOI, Density, Water Content). The procedures for these describe how to make and process the three simple specimens I showed you at the beginning of this chapter (shrinkage bars, H2O bars, drying disk). These provide a framework within which to begin gathering data and relating that to production needs.

The end-product of all your clay body testing work is to generate 'real numbers' that mean something; that can be compared with others to reach conclusions. While the above report may appear a little foreign, it all comes together when you see it in terms of the structured set of variables which are defined for each test. This is a basic report showing gathered data and the results of equations applied to that data. But it is a beginning of a flexible testing system on which much more graphical reports can be built.

So my advice is simple. Set up a little lab for yourself and take control of the physical properties of your clay bodies and materials.

Related Information

Measuring shrinkage/absorption test bars in 1983 at Plainsman Clays

Data for hundreds fired clay test bars was logged into a portable Epson custom programmed HX-20 computer and uploaded to a Radio Shack TRS-80 Model III where it was stored first on cassette, then floppy disk, then a loop tape. That data was later migrated to the Digitalfire DOS 4Sight lab record keeping system (as SHAB specimens) where it lived for more than 27 years (expanding to more than 200,000 tests) until being imported to an insight-live.com account in 2014.

A batch of fired clay test bars in the Plainsman Clays lab

A batch of fired test bars that have just been boiled and weighed, from these we get dry shrinkage, fired shrinkage and porosity. Each pile is a different mix, fired to various temperatures. Test runs are on the left, production runs on the right. Each bar is stamped with a code number and specimen number (the different specimens are the different temperatures). The measurements have all been entered into our group account at insight-live.com. Now I have to lay out and photograph each pile and upload the picture into the code-numbered record. Upon doing so I compare color and tests results to make decisions on what to do next (documenting these in insight-live).

Making a humidity drying chamber - How?

The ideal drying chamber is a tunnel. Starter tunnels pass wheeled-ware-carts single file. Hot dry air enters where the ware exits. The moving air touches all surfaces and picks up humidity as it moves toward the ware entrance. The tunnel must be calibrated so that air reaching the entrance, is still very warm, but of high humidity (laden with water it got from ware down the tunnel). When an equal volume of ware is passing constantly, manual calibration of cart movement, air volume and temperature is possible. But if flow is not constant then your "dynamic system" needs multi-location monitoring and intervention. Locating wireless thermometer/hygrometers and actuators is a good early-start to the project. ESP8266 controllers are revolutionizing industrial control. As cheap as $5, they are tiny but completely capable battery-powered WIFI servers. One of these little things can email you! Even display a web page. These communicate with a central dashboard online (in-plant control systems are now obsolete). There are many online dashboard services that talk to these devices and display results graphically. And it is easy to make your own. Hiring a technician on upwork.com to design a system for you is only a matter of a few thousand (even hundreds) of dollars. Shown here is an Amazon listing for a development kit of an 8266, sensor and cables. I included a listing for a ready-made one, but it is expensive, not well described. A similar product line sells under the name "SensorPush".

Global supply chain issues? Learn to mix and adjust your own bodies, glazes

Shipping containers piled high

Material prices are sky rocketing. And, the more complex your supplier's supply chain the more likely they won't be able to deliver. How can you adapt to coming disruption, even turn it into a benefit? Learn to create base recipes for your glazes and even clay bodies. Learn now how to substitute frits and other materials in glazes (get the chemistry of frits you use now so you are ready). Even better: Learn to see your glaze as an oxide formula. Then calculate formula-to-batch to use whatever materials you can get. Learn how to adjust glazes for thermal expansion, temperature, surface, color, etc. And your clay bodies? Develop an organized physical testing regimen now to accumulate data on their properties, learn to understand how each material in the recipe contributes to those properties. Armed with that data you will be able to adjust recipes to adapt to changing supplies.

Links

Tests Pyrometric Cone Equivalent
Tests Sieve Analysis Wet
Tests Dry Strenth (Round Bars)
Tests Dry Strength (Square Bars)
Tests Density (Specific Gravity)
Tests Soluble Salts
Tests Drying Shrinkage
Tests Firing Shrinkage
Tests Dry Strength (kgf/cm2)
Tests LOI/Density/Water Content
Tests LOI (100-1000C)
Tests Sieve Analysis Dry
Tests Shrinkage/Absorption Test
Tests Sieve Analysis 35-325 Wet
Projects Tests
Glossary Firing Shrinkage
During drying, clay particles draw together and shrinkage occurs. During firing the matrix densifies and shrinkage continues. More vitreous bodies shrink more.
Glossary Drying Crack
During drying clays and porcelains shrink as they become rigid. When this occurs unevenly, cracks are the result.
Articles How to Find and Test Your Own Native Clays
Some of the key tests needed to really understand what a clay is and what it can be used for can be done with inexpensive equipment and simple procedures. These practical tests can give you a better picture than a data sheet full of numbers.
Articles Formulating a Porcelain
The principles behind formulating a porcelain are quite simple. You just need to know the purpose of each material, a starting recipe and a testing regimen.
Articles Stoneware Casting Body Recipes
Some starting recipes for stoneware and porcelain with information on how to adjust and adapt them

By Tony Hansen


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