Where does one catgegorize that West Coast specialty, Claro Walnut? This wood has its own very unique streaking, unlike any of the other walnuts I've seen.
Very briefly, most walnut we see in stocks and blanks come from one of three different species (and one hybrid) of walnut:
Juglans Nigra (commonly called American Black Walnut)
Juglans Regia (aka Persian, English, French, Circassian, Turkish, etc. Walnut)
Juglans Hindsii (commonly called Claro Walnut)
Paradox or Bastogne Walnut, which is actually a hybrid of Juglans Regia and Juglans Hindsii
Of these four species, Juglans Nigra is the predominate Walnut used by gun manufacturers in the USA. In Europe, the Walnut used by gun manufacturers is Juglans Regia. The preference is more about availability than anything else. Outside of the States Black Walnut is an uncommon tree, and Juglans Regia has grown (both cultivated and volunteer) for centuries. Folks use what comes to hand.
American Black Walnut is, as the species name suggests, typically a relatively dark wood. It commonly runs from chocolate brown all the way to black. It can be highly figured with highly contrasting streaking, and in the higher grade blanks vivid greens, yellows, and purples are found.
Juglans Regia, on the other hand, runs the rainbow. English, Persian, and French Regia is typically very light in color. Plain blanks can be almost beige in color and completely bland in appearance. Higher grade blanks will show strongly contrasting pale and dark striping (mineral streaking) or swirling (called ‘marblecake’ figure). Turkish Juglans Regia tends toward reddish hues, strong fiddleback figure, and magnificent marblecake figure. Many of the so called ‘English Stock Finishes’ on the market are attempts to duplicate the reddish cast of Turkish Regia.
Juglans Hindsii is generally found in a thousand shades of light brown. Strong mineral lines are uncommon, and true marble cake figure is relatively rare in Juglans Hindsii. Where Juglans Hindsii shines is in fiddleback figure, which is common in Juglans Hindsii and frequently magnificent. On the plus side, fantastic Juglans Hindsii blanks are relatively inexpensive (about half the price of an equally attractive Juglans Regia blank). On the minus side, Juglans Hindsii doesn’t quite have the compressive strength of Juglans Regia.
Bastogne Walnut is probably the least common of the four species of stock wood. In color it tends to be lighter in color than Juglans Nigra, but is frequently darker than Juglans Regia. Fiddleback figure is not uncommon, and contrasting greens and yellows may be found in the higher grade blanks. Bastogne has the reputation of being the strongest of the four species, and capable of taking very fine checkering ‘best of the bunch’.
Regardless of the species of walnut, mineral streaking and marblecake contrast figure are produced by minerals absorbed by the tree via the ground water taken up by the roots. Sap flow from root to crown distributes the minerals through the tree via the physical grain structure. These minerals cannot be used by the tree and are left in the wood as the wood transitions from sap wood to core wood. How this mineralization presents in a stock is largely determined by cutting plan used to section the tree buttress into stock blanks. Do a google search for plain sawn, quarter sawn, and rift sawn to see how the cut plan determines the presentation of mineralization in stock blanks.
Fiddleback is actually a different subject, and is more closely tied to a tree’s medullary rays than its grain structure.
