A slate is a thin piece of hard flat material, such as the rock also called slate, that is used as a medium for writing. The rock is "a metamorphic rock created by the recrystallization of the minerals in shale from clay to parallel-aligned, flat, flake-like minerals such as mica".
The writing slate consisted of a piece of slate, typically either 4x6 inches or 7x10 inches, encased in a wooden frame.
A precise date range for writing slates of this type has not been established.
Usually, a piece of cloth or slate sponge was used to clean it and this was sometimes attached with a string to the bottom of the writing slate.
The writing slate was sometimes used by industry workers to track goods and by sailors to calculate their geographical location at sea. Sometimes multiple pieces of slate were bound together into a "book" and horizontal lines were etched onto the slate surface as a guide for neat handwriting.
The exact origins of the writing slate remain unclear. References to its use can be found in the fourteenth century and evidence suggests that it was used in the sixteenth and seventeenth centuries. The central time period for the writing slate, however, "appears to begin in the later eighteenth century, when developments in sea and land transport permitted the gradual expansion of slate quarrying in Wales and the growth of a substantial slate workshop industry." By the nineteenth century, writing slates were used around the world in nearly every school and were a central part of the slate industry. At the dawn of the twentieth century, writing slates were the primary tool in the classroom for students. In the 1930s (or later) writing slates began to be replaced by more modern methods. However, writing slates did not become obsolete. They are still made in the twenty-first century, though in small quantities.
Slate itself had been in use as a building material long before it was used for writing. The use of slate as a roofing material can be traced back to at least the Roman era in Wales, from the first to the fourth century AD. The slate used in roofing had to be of very high quality, as the material is prone to cracking and can break if not handled with great care. Slate used for writing slates also had to be of good quality because of the thinness required. Mining slate of this quality is a straightforward process since slate splits into nearly perfectly flat surfaces. The difficult part of the mining process is sorting out the quality slate from slate with "cats" or flaws. Properly sorted slate can be made into any required size. Roofing slate is still in use, primarily for the restoration of eighteenth and nineteenth century buildings, as it is fairly expensive.