The grain of Koa is usually slighted interlocked, which can create difficulties in some machining processes, especially those involving a plane. As noted above, the grain may also be wavy.
The texture of unsurfaced Koa tends to be medium to coarse.
Koa Interior
The endgrain of Koa tends to present as diffuse and porous, with large to very large pores in no specific arrangement. These large pores may require filling if a perfectly smooth finished surface is desired.
Rays in the endgrain may be visible with the use of a lens but they are not visible to the naked eye. Even with a lens the rays are very faint although they can be of a reddish color.
Koa is not resistant to fungal rot, being rated as non-durable to outright perishable. In addition, Koa is susceptible to termite attack. Koa is not a good choice for exterior applications due to these characteristics but given the rarity of the material such uses would seem uncommon as well as unwise.
Working Characteristics
Koa is almost always reported to be easy to work with all hand and machine powered tools and equipment. Koa also usually sands quite well to a very fine finish. However, there are exceptions to this general trend and is so often the case with woods of any species, pieces of Koa that display the much prized heavy figures of curl or wavy grain patterns often also have heavily interlocked grain.
Interlocked grain can be extremely difficult to plane or otherwise machine without tearing or chipping occurring and this is especially heartbreaking when it occurs in the most stunning pieces of Koa. There are no certain solutions to this problem, but patience and extremely sharp tools are an excellent start as is awareness of the potential problem so that corrective measures can be taken. With Koa especially it pays, quite literally, to research the wood you intend to work with before starting your project to be better aware of known pitfalls as well as potential solutions.
Some experts have reported problems with gluing Koa but this appears to be uncommon. Koa is known to stain and finish quite well.
Most relevant to my purposes, Koa is known to be an excellent turning wood.
Koa has no characteristic odor when cut.
Pricing and Availability
As noted in the beginning of this fact sheet, Koa is only found on six of the Hawai’ian islands and the tree has been heavily harvested over time. Simply put, Koa is difficult to find in any great size and when you can find it you will pay a high price. In addition, shipping from Hawai’i is never cheap so when added to the price of the wood itself, obtaining a delivered piece of Koa is an expensive endeavor. In fact, Koa is easily one of the most expensive domestic hardwoods you can choose.
Unfortunately, none of my most commonly used and trusted suppliers of turning woods: West Penn Hardwoods, Bell Forest Products, NC Wood, TurningBlanks.net, and WoodTurningz of Indiana offer Koa at all.
Most vendors of Koa are located, predictably enough, in Hawai’i and as I indicated above, this will result in expensive shipping, although the increasing use of Priority Mail flat rate boxes by wood vendors does help, but the use of those boxes also inherently limits the sizes of Koa that you can obtain for a reasonable shipping cost.
The only time I have purchased Koa, aside from some pen blanks when I was in Hawai’i on vacation (this is an excellent way to buy Koa as you can see it in person and simply carry it back in your luggage for little to no additional cost, provided you are in Hawai’i for some other reason of course) was from a Florida vendor, Exotic Woods USA. I have purchased multiple species from this vendor and the quality is acceptable but it certainly is not of the caliber of the other vendors I have listed above. However, when searching for a wood with limited supply, you sometimes have to take chances. At this time, they only have spindle stock, mostly pen blanks, available, although they continue to show the multiple bowl blanks they have sold in the past on their website for reasons I can’t quite fathom.