Tests

Every ceramic production facility should have some sort of materials, body and glaze testing program in place. Amazingly, many large factories have little or no testing! Then one day the kiln operator notices a large number of cracked, warped and off-size items and everyone in the plant blames him! Likely the real causes are in places earlier in the production. This underscores one of the primary reasons for testing and quality control: To establish specifications and triggers that set off alarms when test results fall outside those specifications. Thus problems can be identified before a product goes to the next step of production.

It is not easy to know where to start when it comes to setting up a testing or R&D program. The huge array of ASTM test procedures, their complexity, test equipment requirements and their expense are intimidating (try finding tests for ceramics on the ASTM website to see what I mean). For testing within your own facility to determine product consistency and suitability consider a simpler and more accessible approach: Characterization of your materials and products in a way that is practical.

Think of it this way: What physical properties of your bodies and glazes are important to maintain? What signals do you need to be sensitive to? For plastic bodies you likely want to monitor particle size distribution, drying shrinkage, water content, fired shrinkage and fired porosity. Two tests (the SIEV test and SHAB test) can provide this information. Consider also the DFAC test for plastic forming bodies, the RHEO test for casting bodies. For production glazes use the GLAZ test to maintain the slurry (other monitoring is of course needed for color, surface, hardness, expansion, etc). Remember, we are just talking about where you start.

Tests in this database are defined as Multi-variable or Single-Variable. Single-variable tests are used to define a value for a specific property. For example, the melting point of a material is specified under the MLPT test and simply appears on pages as a label and a value. Multi-variable tests are where data is being collected and measured over time and the system compiles and computes results and displays them accordingly. Data values for multi-variable tests are recorded with the Sample/Test/Specimen/Variable to uniquely identify them. For example, in the SHAB test one collects the dry length, fired length, fired weight and boiled weight for a number of specimens and the system generates a chart showing the data, the calculated dry and fired shrinkages and the porosity.

Related Information

Links

Articles	Low Budget Testing of Ceramic Glazes There is more to glazes than their visual character, they have other physical properties like hardness, thermal expansion, leachability, chemistry and they exhibit many defects. Here are some simple tests.
Articles	A Low Cost Tester of Glaze Melt Fluidity This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems.
Articles	Simple Physical Testing of Clays 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.
Articles	Understanding Thermal Expansion in Ceramic Glazes Understanding thermal expansion is the key to dealing with crazing or shivering. There is a rich mans and poor mans way to fit glazes, the latter might be better.
Articles	Firing Clay Test Bars Being able to make good consistent test bars and fire them in a consistent and proper way is a basic requirement of getting valid results for shrinkage and porosity measurement.
Articles	Are You in Control of Your Production Process? Potters often run operations that are on the edge of control tolerating production and ware problems that industry would not. However ethics will sooner or later demand a better knowledge of process and materials.
Glossary	Clay Body Porosity In ceramics, porosity is considered an indication of density, and therefore strength and durability. Porosity is measured by the weight increase when boiled in water.
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	Characterization In ceramics, this normally refers to the process of doing physical or chemical testing on a raw material to accurately describe it in terms of similar ones.
URLs	http://www.astm.org/Standards/glass-and-ceramic-standards.html ASTM Ceramics and Glass Testing Standards

By Tony Hansen
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