French chalk

French chalk is a form of steatite.

As an artist's material the term is used by Max Doerner (Artist) in his book "The Materials of the Artist" where he describes a calcium carbonate used to make traditional gesso primer, to be painted over. The favoured chalk used by artists is top quality, 'Champagne Chalk', from the Champagne region of France.

Chalk, calcium carbonate, dissolves in acids with effervescence (carbonic acid escapes). Chalk is unaffected by alkalis. When heated it remains white. It is not poisonous and has little covering power. Impure samples discolor; for example, when they contain iron, they turn red. When strongly heated, chalk is converted into calcium oxide (quicklime). Oil colors that contain chalk "set" quickly in the tubes. The whiter it is, the more valuable it is. When precipitated it is a very fine material. Gray chalks are not useful in grounds; they develop ugly dark spots when touched by oil.

French chalk was a type of solid talc bar used by tailors for marking cloth, by cleaners for removing grease from cloth and as a dry lubricant in its powdered form.

French chalk has also historically been used in the repair of punctured inner tubes of pneumatic tires, such as are found on bicycles. A block of French chalk is typically included in proprietary puncture repair kits, which may include some means of generating a fine powder from the block, for example a small file or a roughened area on the metal case in which the repair kit may have been supplied. The French chalk prevents the repair from sticking to other parts of the tire.

References

• Jmes Smith (1818). The mechanic, or compendium of practical inventions. Liverpool. p. 80.