Here is what Redart fired like in 2010 when evaluated for physical properties using the SHAB test and LDW test. These bars are fired from cone 5 down to 06 (top to bottom). It reached zero porosity between cone 1 and 2. Beyond that it was stable to cone 4. Its drying shrinkage was only 5%, indicating low plasticity (compared to a typical pottery clay), but plenty for casting. It has no soluble salts and a perfect score on my drying performance DFAC test. Cone 04 and 06 porosity and fired color are very typical of terracotta clays.

This picture has its own page with more detail, click here to see it.
This slurry is 100% traditional Redart. This deep red color is a product of the high percentage of iron oxide in its chemical analysis. But that chemistry provides a good example of why using the classical ceramic rational-analysis method to derive a theoretical mineralogy can be misleading for an illitic clay (which this is).
The traditional calculation assumes that K2O and Na2O belong to feldspars, then assigns the remaining Al2O3 to kaolinite and the remaining SiO2 to free quartz. However, Redart is known to be an illitic sedimentary clay. And illite itself contains substantial K2O. That 4.1% K2O is a strong chemical confirmation of Redart containing a lot of illite/mica-type clay. The 1.6% MgO is another clue that some of the chemistry belongs to smectite minerals rather than discrete feldspar and MgO phases.
| Materials |
Redart
The most common commercially 200 mesh available raw terra cotta clay in North America. It fires red, has low plasticity and matures a low kiln temperatures. |
![]() PayPal | No tracking, No ads, No paywall, No transient content! Just organized, concise information constantly updated and improved. Was this helpful? Consider supporting me. |
Buy me a coffee and we can talk