You can really rive almost any wood. That statement is flawed as there are wood species, particularly those with long straight grain, that rive easier than others. It is important to know that species alone is not the key. You want your wood to be straight and relatively free of defects like knots and branches.
The size of the froe can also help determine what it is capable of. Smaller ones would be great for shingles. Larger ones can be better suited for logs. Wedges help if the blade is not as long as the work piece.
Walnut, and more specifically black walnut, is known for splitting very easily and very straight. You will see Roy Underhill praising this wood on occasion if you follow The Woodwright's Shop.
On top of wood species and log selection there are two other tools that are essential when riving (The next more so than the one that follows). If the wood is large or wider than your fore then splitting chisels are your best friend to make sure that the split does not turn as you work.
If you are doing longer logs or feel more conformable with the wood secured then a riving brake is very desirable.
The trick with riving larger wood is to, gently if possible, twist the fore as you go to push the split down the wood. This can speed up the process and it is harder to push the fore when you can hit it dead on with the mallet.
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