Blockx Pastel Chalk, Warm Gray 4. The Blockx pastel chalk range includes 204 vibrant colors. The dry pastel chalk is soft and velvety. It is handcrafted, non-crumbling, and has high opacity. Each pastel chalk is individually packaged in protective foam, allowing for clean handling. Blockx pastel chalk is ready to use, can be diluted with water, and has excellent lightfastness. Size of the pastel chalk: 65 mm Ø 10 mm.