Professional chefs use two tools to keep knives sharp. Slide the entire edge of the blade over a stone (also called a whetstone, pictured), forming a 20-degree angle between the blade and the stone, keeping the pressure even as you draw the blade across from heel to tip. Repeat on the other side. To realign the edges, which get slightly bent with routine usage, draw the blade along a honing steel at a 20-degree angle.