Testing your own native clays is easier than you think

Some simple equipment is all you need. You can do practical tests to characterize a local clay in your own studio or workshop (e.g. our SHAB test, DFAC test, SIEV test, LDW test). You need a gram scale (preferably accurate to 0.01g) and a set of callipers (check Amazon.com). Some metal sieves (search "Tyler Sieves" on Ebay). A stamp to mark samples with code and specimen numbers. A plaster table or slab. A propeller mixer. And, of course, a test kiln. And you need a place to put all the measurement data collected and learn from it (e.g. an account at insight-live.com).

Related Pictures

Get a kitchen blender for mixing ceramic slurries

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Blender mixing is invaluable in slurry preparation in small scale ceramics and testing. It is quick and so effective that not only are particle surfaces wetted much better but clay particles can actually be reduced in size (literally ground finer). Slurry rheology is also stabilized. For example, thixotropy can often be achieved naturally, without any additives. Materials that are otherwise impossible to mix into a slurry (e.g. bentonite, Veegum, CMC gum) are no problem. Even slurry-processed porcelains benefit, not only being more plastic, but firing to a more homogeneous surface and to greater density. Just visually, it is easy to see how much improved this MNP slurry is (a local clay with porcelaneous properties). It was mixed using our propeller mixer and seemed OK (on the left). But the improvement after only 20 seconds in the blender (right) is amazing.

A must-have: Laboratory variable speed propeller mixer

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If you are at all serious about testing glazes and clay bodies, you need one of these. There are other methods, but nothing else comes close to this. It is the most valuable and frequently used tool in any ceramic bodies and glazes testing lab or classroom. These are expensive new, this Lightnin 1/20 hp variable speed cost more than $1000 many years ago, now it could be $4000! But you can get them used on ebay.com, it uses a 7.9mm dia (5/16") shaft. I adapted a mount (to give it vertical adjustment) from a hardware store. Propellers are also expensive, but you can design and 3D print them yourself or have them printed at a place like shapeways.com.

Heavy duty mixer mounted on a steel pole

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It is adjusted so the shaft is at an angle (rather than straight up and down) to pull less air bubbles into the slurry. It can mix up to 5 gallons of viscous glaze or body slurry. The motor is very powerful enabling the mixing of low water content slurries (this means that amounts of less than about 2 gallons of slurry can splatter quite a bit). The 1/2 inch shaft is 22 inches long and the propeller is mounted up from the end of the shaft.

Home-made propeller mixer with mount and switch

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This is a heavy-duty unit, home made, with a 1/3 hp motor. It that can handle 5 gallons of high density suspension glaze or body slurry.

Why you need to make your own glazes, have a test kiln

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Oatmeal cones 6 glazes needs improvements

Are you a potter that depends on glazes made by others? Do you have your ware fired in someone else's kiln? Cannot mix clay body tests? Then the evolution of the quality and aesthetics of your work is being stunted. This mug is a good example of why. This is G3933, made by adding iron, rutile and tin to a 75:25 blend of our base matte and glossy glazes. It is crawling at a few sharp angles of the incised decoration, that means it needs a little CMC gum. I need to switch to an 80:20 blend for more matteness. Third, our red-burning body gives better color at cone 5, I need to test this glaze in the C5DHSC slow cool firing schedule. Finally, I would like the glaze a little darker so I will test increases in the rutile and iron. All of these changes are on my radar because I have my own test kiln and the software to document them.

Links

URLs	https://insight-live.com/insight/help/It+Starts+With+a+Lump+of+Clay-433.html Case Study: Testing a Native Clay Using Insight-Live.com
Glossary	Physical Testing In ceramics, glazes and bodies have a chemistry, a mineralogy and a physical presence. All of these need to be understood to adjust and fix issues.
Glossary	Clay body A term used by potters and in the ceramic industry. It refers to the earthenware, stoneware or porcelain that forms the piece (as opposed to the engobe and covering glaze).
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.
Glossary	Slurry Up The process of slurrying a clay body powder and dewatering it on a plastic slab or table.
Glossary	Native Clay A clay that a potter finds, tests and learns to process and use himself. To reduce the costs of importing materials manufacturers, especially in Asia, often develop processes for clays mined in their locality.
Glossary	Brick Making Brick-making is surprisingly demanding. Materials blending and processing, forming, drying and firing heavy and thick objects as fast as possible are like no other ceramic manufacturing challenge.
Glossary	Insight-Live A cloud-hosted ceramics-targetted LIMS (lab info management system) where technicians manage, develop, adjust and study their recipes, materials and processes.
Tests	Shrinkage/Absorption Test SHAB Shrinkage and absorption test procedure for plastic clay bodies and materials

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