•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
Ceramic engineers and technicians must take control of their production processes to trouble-shoot and have fewer problems, be able to adjust or improve bodies and glazes and formulate new ones. A long term program of quality control measurements is an essential context in which to deal with anomalies in a production process. Where you depend on external suppliers it is doubly important to be measuring (and documenting) the physical properties that most directly impact your process and products.
For example, ceramic glazes fire the way they do mainly because of their chemistry, but also because of the particle sizes of the materials, the mineralogy of the particles and firing and process factors. So no evaluation of a glaze would be complete without testing the physics: Things like the fluidity and bubble population of the melt, the tendency to crack on drying or crawl on firing, the dry and fired hardness, the resistance to leaching, the presence of oversize impurity particles.
The chemistry of bodies is much less important (since the same chemistry can produce radically different results depending on the mineralogy and particle size of the materials). For bodies, technicians want to know about the plasticity; the drying shrinkage and performance; fired shrinkage, tendency to warp and porosity across an range of temperatures, etc. These are physical factors that are very difficult to predict empirically, they must be measured methodically in a laboratory setting.
Often supply and price issues are the main focus in a production setting. Recipes tend to be cast-in-stone and companies are afraid to use new materials where there is not a good context of testing and understanding of the variables that must be managed. Yet, while ceramic engineers and technicians study, compare, research and log a wide range of physical property data for their materials and recipes, a common oversight is an effective way to record and organize the data from them. An account at Insight-live.com is used for this. The extra confidence this brings can have a big effect on company operational efficiency, costs and product quality and consistency. Consider these two examples:
1. Ceramic materials for glazes source oxides to the chemistry; Insight-live has tools to substitute materials (e.g. frits) in the recipe while maintaining the chemistry (and thus fired properties). Videos and training materials at Insight-live provide help so that any technician can accomplish this.
2. As already noted, ceramic materials source physical and fired property contributions to body recipes (e.g. plasticity, fired maturity, lower thermal expansion). In an account at our Insight-live.com your technicians can conduct and document in a very organized way the data for a quality control testing program.
Specification for a Tapper Clay lacks physics
Often ceramic clays are described on data sheets primarily by their chemistry (and requested as such). This is typically done at the expense of physical properties data. For example, Tapper clay is employed to plug the drain hole of ladles used to melt metals in the smelting industry. The operators of that equipment confront, in the physical presence of the material, many properties that have no relation to the chemistry (e.g. plasticity, shrinkage, water content). Notice also that the chemistry is not correct anyway, it species calcined material yet does not total 100. It specifies no carbon, yet this chemistry is like a ball clay, all of which have some carbon.
Lab testing a clay for its physical properties
SHAB test bars, an LDW water content sample and a DFAC drying disk about to be put into a drier. The SHAB (shrinkage-absorption) bars shrink during drying and firing, the length is measured at each stage. The LDW sample is weighed wet, dry and fired. The 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 these measured values.
Why does Tony Hansen take months to unload his kilns?
I love making pottery, but I love the technical side more. I searched for all the test specimens in this load of cone 10 reduction ware first, then pushed it back in and forgot about it. For three months! I really anticipate the test results (I am developing and adjusting many of bodies and glazes at any given time). The data and pictures for them go into my account at insight-live.com, it enables me to compare the chemistry and physical properties of recipes and materials side-by-side. That teaches me which roads to abandon and which ones to pursue. My last kiln went back in for six weeks, so things are getting worse!
Out Bound Links
Glazes become fluid when they melt, they are molten. The fluidity (or viscosity) of this melt needs to be considered, especially when troubleshooting problems. While two different fired glazes may appear to have melted a similar amount (even on a vertical surface), one may be radically more fluid th...
In Bound Links
By Tony Hansen