Opinel are all about traditional methods - if something works why change it. So when it comes to sharpening their blades of course they recommend a natural stone from the quarries of Lombardy, Italy. They been using these stones since the 15th century.
The rock in Lombardy has the right balance of quartz and carbonates in the rock to provide excellent sharpening results. These stones are used with water and are perfect to regular maintenance sharpening. If you have a really blunt blade they you might need something courser to start the process with.
Available in two sizes. The smaller one is spot on for sharpening pen knives and if you'd like to carry it with you. The larger one can also be used for sharpening larger blades and axes.