Thanks everyone.
JP, I know what you mean. I've split two already, possibly because they were not right to start with. Do you think Seth would put some Do's and Don'ts on the forum for those wishing to have a go, without giving too many secrets away?
Firstly, my apologies for the delay in any sort of reply to your enquiry. I have no acceptable excuse save that I really do need to concentrate on getting my act together!
I have acquired most of my practical knowledge and accumulated understanding of working with green 'natural' wood over a period of about 25 years' most of my experience having been gained through trial and error; a process that can be both costly and time consuming. I hope that the following notes will help you to avoid some of the 'pit falls' by triggering some thought and consequential reactions thus enabling you to steer a relatively trouble free course when embarking on future projects.
The Holly blanks shown in your initial thread Ian look very promising. Holly is a good candidate for our needs as a large proportion of the species, of which there are many within the family, have branches that tend to grow in whorls around the main stem, presenting the right configuration for a tamo; however, being a very close grained hardwood timber, it can be quite tricky to season and stabilise without incurring any of the dreaded and unwanted checks.
Working with green wood is not an exact science, there are many variables that have a profound influence on the way one should proceed; not least of these is the classification of timber into either softwoods or hardwoods. It is useful to understand that the terms softwood and hardwood refer to the botanical make up of the wood and not its density or physical hardness. Without going into too much detail, all wood consists of cellulose molecules aggregated, to a lesser or greater degree, into string like units called microfibrils. These microfibrils are encrusted, again to a lesser or greater degree, with lignin; the microfibrils giving the wood its tensile and bending strength while the lignin provides stiffness. Generally though, for our purposes we can categorise softwoods as coming from cone bearing trees, usually with evergreen needle-like leaves, whereas hardwoods come from broad leaved, deciduous trees; there are, however, exceptions to this rule.
Due to the physiological structure of the wood, softwood blanks tend to be easier to work with having supple branches and spurs which, when first harvested, are easily bent into shape; a process further aided by the year round presence of a high moisture content within the wood. Characteristically though a number of softwood species include a high percentage of resin which can be very messy indeed to work with and, in my opinion, these branches are best left on the tree!
Japanese tamos were traditionally made from branches of the Kaya tree also known as the Japanese Nutmeg-Yew (Torreya nucifera); a softwood species chosen for its supple limbs and for the very convenient configuration of the spurs that grow horizontally and opposite each other on either side of the main stem; the perfect alignment for a tamo. The timber, highly prized for its texture and natural beauty, was extensively used for cabinet making, go-boards and other items of Japanese tree, however, due to its scarcity through over cutting, the tree is protected in Japan and wood can only be sourced now from natural mortality. Consequentially a traditional tamo made from Japanese Kaya commands a very high price indeed.
Generally hardwoods have a more complex, compact and finer cell structure than softwoods requiring a different approach to the ways it can be successfully worked. The physical properties of different species varies enormously; some being more accommodating than others in terms of manipulation. It is possible to bend some species of thin, freshly harvested green hardwood spurs into tight hoops providing they are gathered during the growing season when the sap is up. A safer way to proceed, however, is to steam bend moisture laden spurs around a former but, in order to keep the desired shape, the hoop should be left on the former until it has dried out.
For our purposes air drying is the only practical option in terms of seasoning; allowing the wood to reach equilibrium with the immediate surroundings naturally and slowly. The very nature of tamo making means that we are using small stock items of little mass, usually supporting both an inner and outer bark 'overcoat', big factors in our favour in terms of successfully stabilising the wood ready for further treatments. Danger areas that require special attention are freshly cut, exposed surfaces and areas that, for one reason or another, have no remaining bark on them; these surfaces will loose moisture more quickly than 'protected' areas setting up a tension within the wood through shrinkage, usually resulting in the dreaded checks that we are all trying to avoid. It is worth noting that initial drying of green wood, the evacuation of sap, can be allowed to happen quite quickly without too much physical distortion or damage to the wood, however, special care is needed when the process of further reduction in moisture, moisture loss from within the cell walls themselves, is taking place; this must be a gradual process allowing moisture in the enclosed central mass of the blank to continually equalise, through osmosis, with the outer surfaces where evaporation is taking place. An imbalance of moisture at this stage will most certainly cause tension within the wood resulting in an unwanted reaction. This final drying out stage is essential prior to the application of a protective coating but not so critical, however, if a breathable oil finish is planned.
A protective finish of some sort is crucial in terms of preserving the wooden tamo frame from the elements and from general wear and tear, however, the type of finish is very much down to personal preference. Traditionally Japanese tamos were, and in many cases, still are finished with a very durable, natural lacquer made from a corrosive and toxic sap based product called arami; collected during the growing season from the Tea tree (Rhus verniciflera); a genus of the Schumac family, or from the Urushi tree also known as the Japanese Lacquer tree (Toxicodendron vernicifluum). The refined and processed arami is known as urushiol. Urushiol, which is a fairly unfriendly product, requires very precise conditions for it to cure properly and a high degree of expertise in terms of application in order to secure acceptable results. The fully cured finish, however, known as urushi (Japanese for lacquer), provides an astonishingly hardwearing, very glossy, waterproof coating. Other less demanding options include spar varnish, epoxy resin or exterior quality oil; none of these being as durable as an urushi finish, however, they do represent a reasonably hardwearing and practical alternative.
At the present time I have no experience of using epoxy resin as a protective coating so am not in a position to make any useful comments regarding its application or its suitability for our purposes. Perhaps there is someone amongst our readers who has the expertise and knowledge to advise upon the use and suitability of it for our particular needs. Currently my preference is for a good quality spar varnish or an oil finish, the choice being influenced to some degree by the desired final appearance required and by the level of use or miss use the tamo is likely to encounter.
Spar varnish has the advantages of being flexible and of incorporating ultra violate filters; both very useful properties for our particular needs in terms of durability, however, any varnish application is predominantly a surface treatment and, therefore, always in danger of becoming damaged thus threatening the integrity of the intended protection. In order to counter this, all my tamos are treated with 12 coats of varnish in an attempt to reduce the possibility of exposing bare wood should the surface become scratched or chipped. Modern day varnishes claim to withstand the yellowing effect caused through ageing, which is a good thing but, inevitably, yellowing is not completely preventable; becoming more apparent with each additional application of varnish. I find that after applying about six coats onto a light coloured wood, yellowing does start to become a problem. For a truly crystal clear finish I think that epoxy resin may well be the answer.
A well maintained and deeply penetrating oil application, whilst not having the aesthetics of a shiny varnish finish, provides a more robust protection for a tamo that is likely to encounter some really rough treatment; a situation where a varnished surface could be damaged causing unsightly scratch marks or chipping and possibly, in an extreme case, causing exposure of bare wood; a condition to be avoided at all costs as water ingress through 'open wounds', at the very least, could cause irreversible water staining to the wood and possible de-lamination of varnish layers. It should be noted that an oil finish will darken wood considerably and that deeply penetrating oil applications require long curing times and regular maintenance with re-applications possibly on an annual basis; a service I am happy to provide for those who require it.
I am interested to know how your tamos are progressing Ian. Please contact me personally if I can be of any further help to you. In the meantime I shall be posting images of my latest batch of hand crafted tamos within the next few weeks.