Wood to Know: Koa

Wood to Know: Koa

Koa (Acacia koa)

by Peter MacSween

Let’s imagine for a moment you win the lottery. Being an adventurous woodworker, you decide to travel the world to find the most beautiful and inspiring wood. Where would your travels bring you? Africa? South America? I think you will find yourself in the Hawiian Islands home to the Koa tree. 
 
Spectacular is the first word that comes to mind when describing Koa. The heart can be a lustrous, almost metallic, gold with pink, red and purple overtones. Chocolate brown patches can appear, weaving in and out of the background colours.  Sometimes the various colours swirl about creating a marble-like effect. A tight fiddleback curl can also be found in select pieces. Koa also displays a high degree of chatoyance, a visual effect where the appearance of the surface of the wood changes when viewed from different angles. 

WTK_koa
 
Koa is endemic to the islands of Hawaii and is the 2nd most common tree found there. It is fast growing, found at altitudes between 300 feet and 7,500 feet. Koa can be found as short branching individuals or in pure stands where the trees can grow to 100 feet in height and 4 to 5 foot diameters. In the past, some trees were clear of branches for the first 80 feet.
 
Since Koa was such a dominant species on the islands, it became an important resource for the Hawaiian people. Their famous outrigger canoes were carved from a single trunk of Koa with the largest canoes approaching 70 feet in length. It was held in such high regard that eventually only members of the royal family were allowed to possess it. With the declining influence of the royal family over the years, restrictions on Koa were lifted. Koa became a widely used resource and all manner of wooden objects were made from it including fences, household items and ukuleles.
 
Changes started to occur in the 1800’s. Forests were cleared for imported livestock  Harvestable trees were soon in decline. Livestock liked to graze on young Koa trees; so new growth rarely reached maturity. Rising demand combined with increasing scarcity drove up prices and soon poaching and other illegal activities began to take their toll. Koa was in trouble. 
 
With Koa being such an important ecological, commercial and cultural species, conservation efforts began with both government and private landowners involved. Koa is now returning, but harvesting is limited to dead and fallen trees. Some cutting occurs on private land but the yields are small. There is now more Koa growing today than there was twenty years ago. 
 
Woodworkers still have to pay a hefty price for Koa and supply is limited to small pieces, veneer and occasionally 4/4 and 8/4 lumber. Today, it is used for musical instruments where it is an exceptional tone-wood. Turnings, furniture, small boxes and jewelry are common uses today. Items made form Koa abound on the islands as a result of strict export controls.

WTK_koa-endgrain
 Koa end-grain
 
Some compare Koa’s workability to black walnut. It is denser and the grain with uniform texture is often interlocked.  Pieces with interlocked / figured grain should be planed on an angle to minimize tearout. Tooling should kept sharp as it can burn when being routed or cross cut. It can contain silica, which will dull blades. Resin deposits can also occur making gluing difficult. It sands and finishes well. Oil finishes are recommended which makes the colours and figure of Koa ‘pop.’
 
The appearance of Koa can vary considerably depending on the altitude and the island where it was harvested. It will be graded according to appearance and expect to pay high prices for the most desirable pieces. It is recommended you purchase your Koa from reputable dealers. Not only will you be assured that the material was obtained legally, but that the wood is genuine and not some substitute such as Australian blackwood. 
 
A little Koa goes a long way. Small boxes, turnings and other decorative items are well suited for Koa’s distinctive appearance. It will be hard to find pieces large enough for furniture making, unless you are willing to work with veneer or utilize Koa as an accent feature. Perhaps the best strategy is to dream of that Koa project. Be patient and when the right piece of Koa offers itself up, buy it and make that dream come true!
 
 
Average Dried Weight38 lbs/ft³A measure of its weight at 12% moisture and an ambient temperature of 70°F.
Specific Gravity.61A measure of the ratio of its density compared to water (at 12% MC)
ShrinkageRadial: 5.5
Tangential: 6.2
Volumetric: 12.4
Radial (the amount of crosswise shrinkage);
Tangential (the amount of lengthwise shrinkage);
Volumetric (the total amount of shrinkage.)
T/R Ratio1.1A measure of the uniformity of tangential to radial shrinkage.
Janka Hardness1,170 lbfA measure of resistance to denting and abrasion.
Crushing Strength7,060 lbf/in²A measure of compression strength parallel to the grain.
Colour
Color can be highly variable, but tends to be medium golden or reddish brown, similar to Mahogany. There are usually contrasting bands of color in the growth rings, and it is not uncommon to see boards with ribbon-like streaks of color. Boards figured with wavy and/or curly grain are also not uncommon.
GrainSlightly interlocked, sometimes wavy.
TextureUniform medium to coarse.
Workability
Easy to work, and sands well. However, figured wood, or pieces with heavily interlocked grain can be difficult to plane or machine without tearing or chipping of the grain; also, Koa can occasionally give problems in gluing, though this is somewhat uncommon. Koa turns, stains, and finishes well.
Uses
Veneer, furniture, cabinetry, musical instruments (especially guitars and ukuleles), canoes, gunstocks, carvings, bowls, and other turned/specialty wood objects.
Price$38.00 8/4

 
  
Photos and Specifications Courtesy of: The Wood Database