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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.

Key phrases linking here: native clay, found clay, wild clays, wild clay - Learn more

Details

This is the term we use to describe clays in their original lump form, dug straight from the ground. People also call these "wild clays" or "found clays". These are materials that do not have data sheets, their qualities are a mystery until tested or characterized. While a lump clay that a large material supplier mines or imports is "native" from their viewpoint, we use this term to describe materials that a potter or hobbyist might find and process.

Using simple techniques, anyone with a test kiln and basic equipment can characterize on a native clay to determine its properties and suitability.

Related Information

Testing your own native clays is easier than you think


Simple tests being done on a found clay

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).

Step-by-step how to test and evaluate a new native clay


Two lumps of raw clay dug straight out of a hill

"It Starts With a Lump of Clay", a step-by-step Insight-Live.com tutorial (from its help system and the link below) on how to document every step (in an account at insight-live.com) of testing a raw clay. You will learn about drying shrinkage, drying performance, particle size distribution, plasticity, firing shrinkage, fired porosity, fired color, soluble salt content, fired strength, etc. We will not just observe these properties, but measure them. In doing so we will characterize the material. We will answer simple questions about how the material forms, dries and fires across a range of temperatures. In doing the testing I will be generating a lot of data. No single factor is more intimidating to new technicians than what to do with this data, how and where to store it, how it can be searched, learned from, compared.

Plainsman A3 Native Stoneware fired test bars


These are fired to cone 6, 8, 9 and 10 (top to bottom).

Niko Leung uses "wild clays" from construction sites in Hong Kong


Clay block construction

Niko is trained as a product designer so the science and physics of clays and firing require lots of self-learning. She is "salvaging" red burning stoneware materials and hand building these large brick forms for firing between cone 7-8. Drying and firing such shapes without cracking is very demanding. For drying the blocks evenly she made a drying cabinet and put a hot fan to blow in warm air, maintaining an interior temperature of 45C (with high humidity). She puts the blocks on a piece of flat tile and covers them with a cloth to further assist in bringing away the moisture. She is able to fire the pieces on the third day after they have been in the drying tent for 2 days. The drying tent is an idea from the EKWC (European Ceramic Work Centre), these are often used for drying sculptures. Her firing schedule is 80C/hr to 140 with a 1-hour hold, 85C/hr to 650 with a 5-minute hold, 150C/hr to 1130 with a 30-minute hold, 60C/hr to 1230 with a 15-minute hold, 500C/hr to 1130 with a 30-minute hold, 83C/hr to 760.

Clay shmucker


This inch thick iron plate welded to a heavy pipe produces an ideal tool to break down dry clay lumps on a cement floor.

A plaster table: Better than a pugmill, essential for testing


A plaster table

This is an example of an angle iron utility table being made into a plaster table. The cardboard sides extend upward to make the slab thicker and create a buffer gap to prevent the expanding and setting plaster from pressing outward on the frame. 150 lbs plaster (92 lbs water) was poured into the plastic-lined space (the bottom cardboard sections were supported from below). In a dry enough climate, this table could make enough clay to support slurry-to-plastic production for a potter (a thicker slab and a fan would enable even more capacity). The slurry-up process is better than a pugmill for small operations. It's much cheaper and is an easier way to utilize scrap material and weigh out custom recipes. The clay quality and de-airing is better (without hard chunks and contamination common to pugmilling). The procedure generates much less dust and the tank is easily cleaned. Slurries are easily sieved, especially if you have a sieve shaker.

Links

Articles Chemistry vs. Matrix Blending to Create Glazes from Native Materials
Is it better to do trial and error line and matrix blending of materials to formulate glazes or is it better to use glaze chemistry right from the start?
Articles Formulating Ash and Native-Material Glazes
How to have a volcanic ash analysed and them use ceramic chemistry to create a glaze that contains the maximum possible amount of the ash for the desired effect
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.
Glossary Clay
What is clay? How is it different than dirt? For ceramics, the answer lies on the microscopic level with the particle shape, size and how the surfaces interact with water.
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.
Projects Evaluating a clay's suitability for use in pottery
Would you like to be able to use your own found-clays in your production? Follow me as we evaluate a mystery clay sample provided by a potter who wants to do this.
URLs http://www.samplecrusher.com
Portable sample crusher
URLs https://www.facebook.com/groups/558396754685302
Glazes and clays from natural sources
By Tony Hansen
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