Sgian Dubh
Established Member
Mike Garnham":gk566hlr said:
Mike, you might find this lengthy quotation from one of my academic texts useful. On the other hand it may be too much irrelevant information and too dull. Slainte.
"In Europe pink coloured steamed beech is available, and black walnut supplied by large commercial North American drying operations is another species that is sold after steaming. In the case of walnut the purpose of the steaming is to make the sapwood the same colour as the heartwood. Many woodworkers believe the steaming spreads the pigments from the heartwood into the sapwood, but the following quotation argues against this: “The process does not involve diffusing pigment from heartwood to sapwood.” (Tindall, 2007, p 1.)* He goes on to describe the process using purpose built steamers after the kilning operation. The boards are close stacked** and loaded into the steamer, the doors closed, and the inside of the steamer flooded with hot wet steam. As long as the wood rises to the temperature of boiling water, the atmosphere is very wet, and these conditions held for a couple of days the sapwood will turn dark and closely match the heartwood. According to Tindall, when the wood leaves the kiln it looks as if it’s covered in soot, but this planes off to reveal a uniform purple colour throughout. My experience is somewhat different in that more often than not I find the darkened sapwood is only truly dark on the surface and for just a few millimetres (1/8”- 3/16”) below that. By the time I’ve taken two or three passes over a surface planer (jointer in the US) the white sapwood is quite often clearly distinguishable from the dark heartwood. This suggests to me one of two possibilities. The first is that the steaming process is not really as effective as wood technologists and wood processors claim. The second option is that it is effective, but only if the process is undertaken properly. If the latter is true which I have not been able to personally test and verify, this suggests that some of the north American wood processors that steam walnut don’t effectively control or undertake the procedure to get the even colouring.
Many furniture makers object to the steaming process because of the uniform purple colour that the heartwood, in particular, takes on. They prefer the richer and more varied colours of air dried walnut. Whilst I agree that air dried walnut has these attractive characteristics initially, it’s my experience that within a few months, and at most within a year or two of a piece of walnut furniture going into service, it’s usually almost impossible to tell the difference between air dried and steamed walnut. Within two or three years all walnuts exposed to air and ultra-violet light seem to mature into the soft honey browns we’re used to seeing in furniture that’s seen some service, or indeed, many years or decades of service.
The driving force behind the common practice of steaming American black walnut is the main market for the material and the American grading system. Sapwood is not a fault in American grading, and the clearest, least knotty planks come from the outside of the tree during the milling into boards. Naturally, these boards from the outside of the tree contain the most sapwood. The biggest buyers of the wood are big furniture manufacturing businesses, either in North America or, increasingly, overseas with China being one example. Unlike the small furniture business, or amateur woodworker, the big furniture makers generally cut up larger planks to remove defects, rearrange them and glue them back together to make up required widths, and even lengths. So to these businesses, long, wide and clear boards of walnut aren’t their primary concern. If the small furniture maker requires long, wide and clear walnut planks with all the interesting colours to start with, their only recourse really is to seek out specialist suppliers: this almost certainly means paying a premium over the commercially kilned material.
Steaming beech evens out the colour of the boards, but in this case the steaming causes the wood to take on a pink hue in a similar manner to the way steaming walnut causes the sapwood to darken. Steaming beech makes the wood easier to work than unsteamed beech which is naturally a generally off-white brown. Similar to steamed European beech steamed pear takes on a distinctive pink tone. Pear species treated this way come from a range of the Pyrus genus, but generally only the Pyrus nivalis (Swiss pear) and Pyrus communis (common pear) produce timbers big enough for larger furniture parts and veneers. Fairly new on the market to me is steamed north American birch for sale in timber merchants and the process in this instance gives the wood an even rich chocolate colour.
*http://www.woodcentral.com/articles/reviews/articles_894.shtml
**Close stacked aka ‘dead packed’ timber describes packs of dried boards or planks stacked tightly together with few or no spaces. A couple of advantages of close stacking are: boards maintain their dried MC better through prevention of air circulation, and take up less space during storage and transport."
