This is the term we use to describe clays in their original lump form, dug straight from the ground. These are materials that do not have data sheets, their qualities are a mystery until tested. While a lump clay that large material supplier mines or imports is "native" from their viewpoint, we also use this term to describe materials that a potter or hobbyist might find (often called "found clays"). Using simple techniques, anyone with a test kiln and simple equipment can do a characterization on a native clay to determine its suitability in their production.
These are fired to cone 6, 8, 9 and 10 (top to bottom).
Some simple equipment is all you need. You can do practical tests to characterize a clay in your own studio or workshop. You need a gram scale (accurate to 0.01g) and set of calipers (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, and learn from, all the measurement data collected. An account at insight-live.com is perfect.
"It Starts With a Lump of Clay" (link below) is a step-by-step Insight-Live.com tutorial (from its help system) on how to document every step (in an account at at insight-live.com) of analyzing a raw sample of clay. You will learn things 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 do to with this data, how to store it, where to store it, how it can be searched, learned from, compared. This tutorial will erase that question.
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 your glazes or is it better to use glaze chemistry?
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
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.
What is clay? How is it different that regular dirt? For ceramics, the answer lies on the microscopic level with the particle shape, size and how the surfaces interact with water.