A chalk line is a tool for marking long, straight lines on relatively flat surfaces, much farther than is practical by hand or with a straightedge.
It is an important tool in carpentry, the working of timber in a rough and unplaned state, as it doesn't require the timber to have a straight or squared edge formed onto it beforehand.
Chalk lines have been in use since ancient Egypt, and used continuously by builders in various cultures continually since . Continuing development of this simple tool focuses on the coloration for the chalk or marking compound, as well as the outer case and method of handling.
A chalk line draws straight lines by the action of a taut string. Specifically, the string (previously impregnated or coated with a loose dye such as chalk) is laid across the surface to be marked and pulled tight. The string is then plucked
or snapped sharply to cause the string to strike the surface, leaving a straight line. The primary problems associated with improper maintenance of a chalk line are string breakage due to excessive tension on the line, and degradation of the line associated with moisture contamination.
In Japan, an ink line is used in preference to a chalk line. This is a silken cord, stored on a combined reel and inkpot called a sumitsubo
. Alongside the line reel is a cavity filled with ink-soaked cotton fibres, which the line is drawn through as it is unreeled. These sumitsubo are highly decorated and much-prized by their owners. As with many such tools, they're often made by their users whilst apprentices.
On the completion of a major building, such as a temple, a large celebration or topping-out ceremony is held. As part of this event, a set of symbolic carpenter's tools are freshly made and presented to the new building. A sumitsubo is a traditional tool included with them.