More recent studies further classified base water as temper water and free water. Temper water being the water held within the clay platelets. Whereas free water is water that is not bound in the clay and can be problematic. Free water can cause penetration and surface defects, steam generation during pouring, and dimensional instability. There is currently not an accepted method to calculate and differentiate between free water and temper water.
Figure 1: Temper Curve in R. Heine’s paper Compactibility, Green Strength, And Moisture as Related to Green Sand Processing Efficiency. It shows the relationship of Green Compressive Strength, Percent Moisture, and Percent Compactability to Percent Clay in fully processed green sand.