Keson Prochalk Permanent Waterproof Chalk Dye (3 Lbs.) - BlueKeson ProChalk Permanent, Waterproof Chalk Dye (3 lbs.) Blue Level 4 Performance Waterproof Permanent Marking Dye ProChalk Permanent chalk for weatherproof and waterproof lines that arent going to go away any time soon. Most users are choosing this level of intensity for applications that are going to be covered. This level is engineered for more extreme conditions. Exterior applications include exterior layout, extreme conditions, concrete layout,