During baking, the crust of a free-form loaf is likely to burst open as the dough swells rapidly (see oven spring), leaving an unsightly split and distorting the shape of the loaf. By making cuts or slashes in the surface of the dough, the baker creates a weak fault-line that should open out and allow the loaf to expand in a controlled way. These slashes are usually made to be decorative as well as functional, and some bakers have their own signature style of slashing loaves. Tin loaves are not usually slashed as the crust tends to break open naturally along the rim of the tin in a fairly even way.
Many bakers use a tool called a lame or grignette to slash the dough; a sharp knife or a pair of scissors can also be used. French bakers refer to the slashes as grignes.
Want to find out more? Look at the chapter on shaping in the book flour and water.
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