Terra alba is a natural gypsum that can be used as an extender in paint and filler in grounds. Terra alba, calcium sulfate dihydrate, is made by fine grinding and air separating a select, high purity, white gypsum from Italy containing about 20% water of crystallization. Depending upon vapor pressure, relative humidity, loading levels, etc., this water of crystallization, or combined water as it is often called, starts being released as the terra alba is heated above ~50 °C. By about 180 °C, 75% of the combined water has been released. Water is not totally removed until temperatures exceed 400 °C. In formulations processed at room temperature, terra alba can also function as a flame retarding filler.
| Properties | |
| Chemical Name: | Calcium Sulfate Dihydrate |
| Chemical Formula: | CaSO4 • 2H2O |
| Specific Gravity: | 2.32 |
| Mohs Hardness: | 2–3 |
| Loose Bulk Density (lbs./ft.3): | 42 |
| Packed Bulk Density (lbs./ft.3): | 62 |
| pH (10% Slurry): | 7.3 |
| Refractive Index: | 1.52 |
| Oil Absorption: | 23–25 g oil / 100 g pigment |
| Reflectance (HunterLab D25-PC2 Colorimeter L,a,b values): | 89.1, –0.9, 2.9 |
| Median Particle Size (microns): | 12.0 |
| Largest Particle Size (microns): | 150 |