Woods to Know: Peruvian Walnut

Woods to Know: Peruvian Walnut

Peruvian Walnut (Juglans neotropica)

by Peter MacSween

The walnut family has many species that catch the eye of woodworkers. European Walnut offers distinctive figuring and swirling colouration. North American black walnut is famed for its purple-black patina often with curl and other 'eye candy.' But both walnuts have their issues. European Walnut can be scarce and expensive while Black Walnut is knotty, sappy and comes in increasingly small dimensions. 
Perhaps its time for woodworkers to consider the tropical cousin Peruvian Walnut (also known as Nogal). Peruvian Walnut is the most common species of a group of related trees, all members of the genus Juglans.  Some refer to these species as Tropical Walnut; however, for this article I will use the name Peruvian Walnut as the reference species. We have the most information on it and the differences between the species are mostly due to colouration, which more than likely reflects their country of origin. 
Peruvian Walnut is mostly harvested in Peru and its close neighbours. Other species of Tropical Walnut are found in Mexico, south through Central America and into northwestern South America. Peruvian Walnut is a medium size tree, 30 - 60 feet high with diameters of 2 - 3 feet. It is similar to all walnuts in having large compound leaves and bearing large nuts which are a minor food source in Ecuador. 
Peruvian Walnut has a deep chocolate-brown heartwood with occasional purple streaks. Somes species may have areas of lighter colouration. However, unlike Black and European walnut, Peruvian Walnut colouring is very consistent, and it does not have a sharply demarcated sapwood. The grain is straight, occasionally irregular with a medium to coarse texture. Figured woods such a curl and fiddle-back are extremely rare. 

Peruvian Walnut is difficult to dry especially when drying lumber thicker than 4/4. In fact, I have never encountered any other thickness than 4/4. The wood must be air dried before putting it into the kiln. While patience is required (pieces may take up to 3 years to dry), Peruvian Walnut is still prone to honeycomb and kiln collapse. Once dry, it is stable. but it is prone to insect attack, so it is mostly used for interior applications. 
The wood is very easy to work by hand or machine. Irregular grain may tear, so keep your tools sharp and keep an eye on cutting angles and feed rate. It takes nails and screws well. There is no problem with gluing either which is an important consideration if you are gluing up thinner pieces to make larger dimensional lumber.  It has a natural luster which makes for a beautiful finish. It stains very well and this makes it easier to obtain a consistent colour if you happen to purchase some boards with lighter coloured streaks. 
Peruvian Walnut is a good choice for furniture and cabinetry. It is used architecturally for flooring and trim. Its darker colouring is often used in intarsia projects, inlays and whenever a contrasting visual effect is desired. Luthiers use it for guitar necks, backs and sides as well as solid guitar bodies.It is also used as gun stock material. Since it slices and peels easily, it is commonly used as a decorative veneer.

Peruvian Walnut end-grain
The primary appeal for woodworkers who like to work with the walnuts is Peruvian Walnut's consistent colour and the fact that knot free boards up to 14 inches wide are available. While it is more expensive than Black walnut (though moderately priced for an imported wood), once waste factors are considered, it is a very competitive product. If you choose to work with Peruvian Walnut, you should sort for consistent colouring. Small colour imperfections can be dealt with at the finishing stage. Areas of 'open' grain may be present. These probably are from drying defects which can be surfaced away. Remember, like all walnuts; Peruvian Walnut can produce eye, skin and respiratory effects. Please use appropriate protection until you can ascertain your own sensitivity. 
Peruvian Walnut is not on the CITES list of endangered species requiring regulation, but it is on the IUCN list as species under population pressure due to habitat loss and exploitation. This can pose problems for woodworkers when they are considering project materials. To solve this problem, craftspeople can design projects with the goal of reducing waste and making items that last for generations. We should be at the forefront of building a sustainable future for the woods we appreciate, and Peruvian Walnut used wisely can help preserve native walnuts by acting as a substitute.  
Average Dried Weight37 lbs/ft³A measure of its weight at 12% moisture and an ambient temperature of 70°F.
Specific Gravity.60A measure of the ratio of its density compared to water (at 12% MC)
ShrinkageRadial: 3.6
Tangential: 7.5
Volumetric: 11.4
Radial (the amount of crosswise shrinkage);
Tangential (the amount of lengthwise shrinkage);
Volumetric (the total amount of shrinkage.)
T/R Ratio2:1A measure of the uniformity of tangential to radial shrinkage.
Janka Hardness960 lbfA measure of resistance to denting and abrasion.
Crushing Strength6,550 lbf/in²A measure of compression strength parallel to the grain.
Heartwood tends to be darker than temperate walnut species, with a deep chocolate brown color, sometimes with a purplish hue. May also contain streaks of lighter-colored wood mixed throughout the heartwood, which can sometimes be extensive and result in a high degree of waste. Grain figuring such as curl seems to be much less common than other walnut species.
GrainStraight, sometimes irregular.
TextureMedium to coarse.
Typically easy to work provided the grain is straight and regular. Planer tearout can sometimes be a problem when surfacing pieces with irregular or figured grain. Glues, stains, and finishes well.
Furniture, cabinetry, veneers, flooring, musical instruments, and interior trim.
PriceSupplies can be erratic. Check with your local dealer.
Photos and Specifications Courtesy of: The Wood Database