The Cascara Buckthorn tree has long been known for the laxative properties of its bark. Stripped in the spring, dried, bottled, and marketed as Cascara Sagrada, the bark was in such high demand in the early-to-mid 20th century that the small trees were severely overharvested. Harvesting cascara bark entails killing the tree, and so throughout much of its native range, primarily the western side of the Cascades in the Pacific Northwest, cascara, never very abundant, became quite scarce. (In my woodturning club, some members whose fathers or grandfathers had once made a living as "chittam bark" peelers, had never themselves seen the tree or the wood.)
Cascara buckthorn, Rhamnus purshiana, grows at lower elevations in moist areas like those suitable to red alder. In such conditions a mature tree may grow to 35 feet tall, and no more than 12 inches in diameter, usually smaller. It has rather large, somewhat glossy leaves with prominent veins, and bears a modest crop of 1/4" berries that ripen from red to glossy purple-black in late August. These berries are eaten by many birds, as well as bears, raccoons, and other animals.
Fortunately, the seeds benefit from passage thru the guts of animals and birds, and the latter have no doubt been highly instrumental in redispersing the species through much of its former range. When I identified my first cascara tree, about 1990, I knew of only two on my property. By the time I sold the place in 2004, I had discovered several dozen additional trees on the forty acres, almost all less than 20 years old. One cluster of several vertical tree-sized branches had sprouted from an older trunk which apparently had fallen or been pushed over, but remained rooted.
Because cascara is such a small tree, the wood itself is considered to have no commercial value. Therefore, the stripped trees were most likely left to decay, or possibly cut for firewood. But I have discovered that it is a very nice turning wood, with subtle character and often, surprising color.
When freshly cut, cascara sapwood is a pale yellow, and the heartwood, which makes up about a third of the diameter of the trunk and larger branches, is almost a pumpkin orange. As the wood dries, the sapwood seems to get paler, and the heartwood color becomes more muted. Drying also seems to induce unexpected color zones in the sapwood, which I am still studying to try to determine their cause. In the picture at the top, you can see darker areas in the sapwood of the log section, which appear as purplish streaks on the box. The wood here was perfectly sound, so it doesn't seem to be related to decay, the way spalting is.
Just outside the heartwood in the log is a barely perceptible ring, which unfortunately did not appear on the box made from the adjacent section. A few years ago I found a long, dead branch hanging from one of the trees. It was sound and perfectly dry, and just inside the outermost edge of the sapwood, was a ring of color that I have not seen in any fresh-cut branches.
I made these little weedpots by centering the branch so that the belly curve would pass thru the color ring. Note the subtleties of color. The rings often have pale pastel shades of blue and purple, plus hints of sage green and gray. They look like they are painted on!
[Update 20100301: I swapped out the original picture for a better one showing the "picture frame" effects, and edited the text accordingly. Lea]
I also made a small, straight-sided cup from this branch, but unfortunately, while the colors were even more visible, the photos I took were out of focus, and I no longer have the piece.
After the 2004 ice storm, several of the larger, more exposed trees on my property were severely damaged, with their branched tops bent ninety degrees and the wood splitting at the bend. I cut these trees into long sections, sealed them, and put them aside to dry. Based on the faint ring that has appeared in the one log section, after only a year of drying, I am hoping that some of the other pieces may develop color rings as vivid as this branch.
Even without the color band, cascara can be very beautiful. The fine-grained sapwood displays a subtle chatoyance, almost like the moire patterns in fine curtains. On one of the larger trees I took down, the cross-section revealed that every growth ring was finely rippled, like the edges of paper cup-cake pan liners. Now that will be some spectacular wood in four or five years!
I am most careful not to put my hands near my mouth when working this species. Otherwise, I take only normal precautions against dust and chips when turning cascara, and have experienced no side-effects from the bark, even when turning it green.
Dry cascara turns easily. The wood is fairly hard, about like big-leaf maple, and shows no tendency to chip. It polishes up beautifully, as you can see, and I have used only clear shellac or, on the weedpot, just beeswax, to avoid darkening the colors. My first attempt to turn green cascara, however, was rather a disaster. There was a very noticeable difference in density between the heartwood and the wetter sapwood - the latter seemed almost to shred and I ended up with something akin to firewood rather than a turning. In hindsight, much might have been due to poor technique or less -than-sharp tools, but at least some of it was due to the wood itself.
A fascinating and unexpected fact about cascara, which I only learned recently, is that it is closely related to Pink Ivory, Rhamnus zeyheri. Pink ivory, which grows in southern Africa, is considered one of the most rare, expensive, and beautiful woods in the world. In my opinion, cascara, its humble North American relative, is also deserving of some respect.
Update 20100301: The broken picture links have been fixed.
cascara, pink ivory, woodturning