Why is my bag of red clay so stiff compared with other types of clay?

Potclays red clay bodies are manufactured to a hardness (NGK reading) of between 6-8, tested with an industry-standard penetrometer at the end of the pugmill prior to bagging. The reason these bodies are made to a firmer NGK range than other clay bodies is due to the thixotropic nature of red clays. If the NGK is too low, it causes problems in production as the machinery cannot process the clay effectively. Furthermore the vibrations in transit will cause the clay blocks on a pallet to distort considerably, which leads to other issues. For a softer consistency for throwing, thorough wedging and kneading will help to a degree. Clay can be softened further using the Evolution Stoneware approach (see YouTube video)