Woods to Know: Purpleheart | Canadian Woodworking & Home Improvement

Woods to Know: Purpleheart

Purpleheart (Peltogyne spp.)

by Peter MacSween

The memories of my first encounter with Purpleheart are still strong.  After years of working with domestic woods, it was hard to believe wood could be that colour.  Seeing Purpleheart opened up the world of exotic woods to me.  New woods meant new ideas and new projects to imagine and to build.  
 
It’s not only its colour that make Purpleheart an impressive species.  It is a truly large tree growing to 170 feet in height with diameters of 5 feet.  The trunk is often buttressed at ground level and can stretch upwards for 75 feet before any branches are encountered.  These trees can produce large amounts of clear lumber in decent lengths and widths.
 
There are over 20 species of Purpleheart in the genus Peltogyne, with all of them exhibiting a different shade of purple in the heartwood.  Purpleheart grows in tropical Central and South America from Mexico south to the Amazon Basin in Brazil.  Mexico can claim one species of Peltogyne, while the rest of the harvested species come from Brazil and neighbouring countries.
 
The purple colour of the heartwood is the result of extractives the tree deposits in the heartwood as it grows.  These chemicals, while appealing to woodworkers, serve to make the heart resistant to insect and fungal attack.  Purpleheart is a wood well suited to exterior applications, and it is used for framing, dock pilings and even train track ties in its native countries.  The sapwood is a creamy grey and is distinct from the heart.

WTK_purpleheart
 
The wood is straight grained with a natural luster.  It is not uncommon to encounter interlocked or irregular grain, which can make the wood hard to work.  Purpleheart is also heavy, dense and very strong.  These characteristics can add to the burden of working with it.  If you use dull tooling and slow feed rates, the wood can be heated until it releases resins that can clog blades and cutter heads.  Purpleheart can burn when being routed and these burnt areas are difficult to sand out given the wood’s hardness.
 
Woodworkers should use sharp tools and monitor cutter speeds for burning.  Screws should be predrilled and, to be honest, I wouldn’t even try nailing it.  It glues well, although too much clamp pressure can squeeze out glue and starve the joints.  Some woodworkers recommend wiping fresh cut surfaces with acetone or lacquer thinner to remove any resins that can interfere with a successful glue up.
 
In the end, it all comes down to showcasing that bright purple colour.  First of all, when selecting Purpleheart, try to use a single species.  The 20 or so species all have a subtle colour of their own and often are mixed together when sold.  The heartwood of all species is a purply to brownish grey and will only turn to purple once it is cut.  Over time with exposure to air and light the bright purple heartwood will change to very attractive purple brown. 
 
You can’t stop this colour transition, but you can slow it down by using a film finish with UV light inhibitors.  Water based film finishes will dry clear and will also not yellow over time.  If you want to use an oil-based finish that is absorbed into the wood, it must offer UV protection as well.  These finishes do not offer the same colour protection as film finishes.  The colour can be revived by sanding or using a plane on any oxidised surfaces, although this isn’t always possible with finished pieces. 

WTK_purpleheart-endgrain
Purpleheart end-grain
 
Purpleheart can be visually overwhelming if it is used on large surfaces.  Most woodworkers use it as a colour accent or detail.  It is very common in inlays, small decorative objects, pool cues and other turnings.  It is a good choice for flooring if you are willing to wait for the colour change or as accents in parquet.  It is also sliced into veneer and has been used in architectural applications.  Other applications include marquetry, knife scales and musical instruments.
 
Purpleheart is facing export restrictions in some countries due to overharvesting.  But the population as a whole is not considered threatened and there should be plenty of Purpleheart for many years to come.  The price is attractive for an imported exotic; so the next time you are at your favourite wood shop, feel free to indulge your fantasies and purchase some of this outstanding wood.
 

Average Dried Weight56 lbs/ft³A measure of its weight at 12% moisture and an ambient temperature of 70°F.
Specific Gravity.90A measure of the ratio of its density compared to water (at 12% MC)
ShrinkageRadial: 3.8%
Tangential: 6.4%
Volumetric: 10.6%
Radial (the amount of crosswise shrinkage);
Tangential (the amount of lengthwise shrinkage);
Volumetric (the total amount of shrinkage.)
T/R Ratio1:7A measure of the uniformity of tangential to radial shrinkage.
Janka Hardness2,520 lbfA measure of resistance to denting and abrasion.
Crushing Strength12,140 lbf/in²A measure of compression strength parallel to the grain.
Colour
When freshly cut the heartwood of Purpleheart is a  dull grayish/purplish brown. Upon exposure the wood becomes a deeper eggplant purple. With further age and exposure to UV light, the wood becomes a dark brown with a hint of purple. This color-shift can be slowed and minimized by using a UV inhibiting finish on the wood.
GrainUsually straight, but can also be wavy or irregular.
TextureMedium
Workability
Working with Purpleheart can present some unique challenges: if the wood is heated with dull tools, or if cutter speeds are too high, Purpleheart will exude a gummy resin that can clog tools and complicate the machining process. Depending on the grain orientation, can be difficult to plane without tearout. Purpleheart also has a moderate dulling effect on cutters.
Uses
Inlays/accent pieces, flooring, furniture, boatbuilding, heavy construction, and a variety of specialty wood items.
Price$15.00/bf, 4/4 lumber
For a list of Canadian retailers click here

 
  
Photos and Specifications Courtesy of: The Wood Database