"Gates To The City", bamboo sculpture by Cal Hashimoto
Hi! I'm Cal, a bamboo sculptor. I started working with bamboo as an art medium about 17 years ago and at that time there was very little published to guide me in the techniques necessary for producing art of enduring quality. In the ensuing years of experimentation and some successes and a whole lot of failures I developed methods that met the requirements specific to my bamboo work.
It would require an entire book to share what I've learned thus far, so given the limitations of this article I will briefly cover a few areas of my techniques that I consider important, with hope that this brief abstract will stimulate those interested readers to higher levels of bamboo craft.
The excitement and anticipation of producing any creation begins with a vision. I begin with rough sketches that eventually evolve into a scale drawing or a three-dimensional model. If the final product is of value to you, the more refinement the better as the process of refinement will reveal flaws in concept that are much easier to fix in the design process than later on when you are in the process of fabrication. Time spent on design should also give you a pretty accurate idea of the types and amount of material you will need. On the other hand, I many times started from an inspired idea in my head straight to process, which has much value also — less reliable and predictable, but it was essential to my own curiosity and learning curve.
My designs are many times based on the bamboo stock that I have on hand, but if additional sizes/varieties are required, I rely on trying to locate the required material at a local retailer. The latter endeavor is often met with frustration, so I try to keep a variety of bamboo culms in storage for that eventuality.
Most bamboo culms available in retail outlets are supposedly cured and treated for insects, but my experience is that the quality control at the place of origin still remains questionable.
I do harvest a few varieties of bamboo that are common in my vicinity that are suitable for my work. Do refer to the ABS Species Source List under "Comments - Description" for varieties that are recommended for crafts/construction if you intend to harvest yourself, as not all bamboos are created equal. If it's not on the list and you want to give it shot anyway — go for it! — life is short....
When I harvest, I try to pay close attention to the best time of the year and optimum phase of growth in regard to when harvest should take place. There are numerous books and articles you can refer to in this regard. I also highly recommend that you choose culms of maturity — meaning culms that are 3-7 years of age. Younger culms have not established the lignin and cellulose in the cell structure for greatest strength and the older culms tend to be brittle and structurally unpredictable. Dead culms are generally junk and better composted.
If bamboo is harvested under optimal conditions, there is a much better chance of avoiding insect infestation. Some varieties are also inherently less prone to attack. If I want assurance about protection then I will use preservation techniques. As I am not using bamboo in high volume, I find the Vertical Soak Diffusion method accommodates my needs (see writings by Dr. Liese on VSD). I start by standing the newly harvested culms (10-12' lengths) under cover and not in contact with the ground to dry for about three weeks. I then knock out all the septums except the bottom one with a length of steel rebar. The culms are then filled with a borate preservative (Solubor - US Borax - an agricultural soil additive - one lb. to one gal. water) and kept topped off for about 10 days. After that, empty the culms and store vertically for a minimum of 2-3 months. If stored for more than a year, I find the bamboo becomes more difficult to work with in certain procedures.
Some varieties of bamboo have a slightly porous surface and, with cleaning or light sanding, a finish can be applied directly. However, most of the bamboos that I use, especially those of the Phyllostachys genus, have a hard waxy surface and I've found that if the "wax" is not removed, then applied finishes may not adhere properly and may peel off at a later date. One can remove the skin entirely and then finishes will be durable, but in my opinion one loses much of the inherent natural beauty and essence that makes bamboo unique. For this reason, I use heat to remove the "wax" as an initial stage of material preparation so the finish can be successfully applied.
Besides using heat to remove the "wax" there are reasons for this process that results in other enhancements to the material:
I use a number of propane heating devices, but the one that I use the most is a commercial torch (Goss) used by professional plumbers with a 1-1/4" diam. flame tip connected to a five-gallon supply tank. The processes involved with removing the wax, straightening and altering the color of the culms require far more words than this article affords. There is information currently available however, but that will require research on your part.
Part of the reason I spend time on drawing an accurate scale drawing is that it allows me to take the drawing to a print shop and have it digitally blown up to a full-size image that I fasten to a work surface so I have a template to follow in the fabrication process. It is an accurate and inexpensive method to guide me and avoid major mistakes. This is a guide only and artistic license is encouraged.
Whenever I am performing an operation on a piece of bamboo — whether it be cutting, drilling, notching, or any procedure that exerts force on the material — it is mandatory that the piece be secured. I use a variety of different "V" shaped cradles for different operations. Bamboo is akin to a long, slippery, ball-bearing and as such will tend to roll when worked on and, if not secured, may result in unintended damage to the piece or more importantly, to yourself. I also pad some of the cradles with carpeting for greater purchase and to avoid damage to the bamboo surface.
For cutting bamboo to size, I generally use a 10" power miter saw with a fine-toothed carbide blade (min. 60 tooth or better). A fine-toothed Japanese hand saw that cuts on the pull stroke is adequate also. In either case, I use blue masking tape over the area of the cut to avoid splintering and tear-out. When doing angled cuts, it is important that the direction of the cut follows the grain of the culm. For marking the cuts, I use a grease pencil or water-based felt pen directly on the culm or the tape, the reason being that the marks can easily be removed later.
A sharp standard twist bit is adequate for small holes (up to 3/8" diam.), but for larger holes I use brad point, Forstner or hole-saw bits for the cleanest cuts. For especially clean cuts I tape the area of the hole. Always use some form of cradle to secure the piece if possible. Also use a drill press with a cradle when a clean cut is especially required. To adjust the size or shape of the hole I use a die grinder (see NOTCHING).
There are a numerous ways to notch bamboo. One is to lay the bamboo to be attached on the piece to be notched and transcribe an outline of the notch by eye. Saw parallel cuts within the outline of the scribe and pry them out with a screwdriver. This will remove most of the material very quickly. To take out most of the remaining material I use a die grinder — a high-speed rotary tool that is like a very large Dremel. I prefer to use carbide burr bits as they will remove material quickly and leave a fairly clean cut. Take note that the rotation of the bit needs to go with the grain of the culm on the side of the notch you are grinding on. For final fitting, I use a drum sander chucked into a 3/8" variable-speed, reversible hand drill. Choose a drum diameter that is near, but smaller than the diameter of the notch. Again, pay attention to the rotation of the drum relative to the grain.
When I have a good fit of the two culms at the notch, I scribe the un-notched bamboo, in place, with a sharp, pointed dental tool. This indicates the area of the mating surface of the un-notched culm to the notch, which needs to be roughed up in preparation for gluing. If the skin is not removed or roughed up at the mating surface, the glue will not have good adhesion. I use a good quality carpenter's glue or hot polyurethane glue for best results. If you use a glue with a reasonable setting time, I recommend lashing the joint tightly with strips of inner tube or surgical tubing for a pressured fit. When the glue is set, I will set a screw at the center of the junction of the two culms and lash the joint in a way that covers the screw and the intersection of the two culms. This method results in an attachment that is extremely strong, as there are four connective methods employed.
As stated before in Material Preparation, if the bamboo I am using is of the Phyllostachys genus or has a similar waxy surface, then it is necessary to heat-treat the bamboo so the finish will have good adhesion.
For complex assemblies that require a finished surface on all sides I sometimes find the best results are accomplished by pre-finishing the individual parts before assembly. In other cases when I can get clear access to all surfaces, I use an air brush for smaller elements or an automotive touch-up sprayer for larger ones. An aerosol can also works. I recommend practice before starting on the final product. I understand using a brush works also, but I'm just not a brush kind of guy.
Polyurethane is a very durable finish, but when there is high humidity, the drying time can be several days per coat. I use pre-catalysized lacquer that is also a very durable finish and dries quickly. For pieces that have UV and some weather exposure I use Cetol 1 & 23 by Sikkins. I generally apply 2-3 coats for best protection.At this point this article may have brought up more questions than answers, which is an indication to me that I have stimulated your interest. In an article this short, on a topic so broad, this is about the best I could hope for. For what it's worth, this dollop of information is a heck of a lot more than I started with when I began working with bamboo. Bamboo is a unique and beautiful material and for those of you with the tenacity to fathom its characteristics — I salute you —good luck! - Cal
For more artwork, see Cal Hashimoto’s web site.