What is a chalk line? Chalk lines are commonly used in the building and construction industry to easily ‘draw’ a straight guide line between two points. The chalk is distributed over the string, to make a marking. 

Blue chalk powder is considered to be for general purpose use and will contrast well on wood, plastic and metal surfaces. Blue chalk is generally considered to be general purpose and is temporary - ideal for use on surfaces which will be visible once the job is done. 

Red chalk powder is highly visible and will contrast well on nearly all surfaces and materials. If you need a more permanent mark for a longer term outdoor project, which will not wash away in the rain, red chalk will be a more suitable option.