I do love a bit of burr!
For me, there is no finer piece of timber than one which has what was once called a defect, but which we now like to think of as a natural feature. Thankfully, my attitude is much the same as that of a growing number of wood turners and, I’m glad to say, as that of many of my customers as well; if a feature of the timber is a result of a natural process, then it cannot possibly be a fault, it is simply a natural feature. Rather than condemn the timber to the firewood pile, we should celebrate such features and learn to incorporate them into our work.
Over the next few months I will take a close look at several features that occur in timber, but I’ll start with the burr, or burl as it is known in many countries. So what causes a burr? Quite simply, the tree responds to a stress or trauma, by producing new growth deep within its trunk, and by sending a new bud to the surface where it breaks through the bark. This bud starts its life close to the very pith of the tree and if we were to take a plank of timber from that part of the trunk, we would simply see the new growth passing through the plank as a small knot. However, the tree produces numerous such growths close together and they each compete for space as they grow, colliding and distorting, forming a mass of knots and often an intricate grain pattern.
Whilst still a part of its host tree, a burr contains a mass of stresses, all held in balance, but the moment that the burr is cut, then an imbalance of stresses occurs and the timber starts to warp and twist, and it will probably develop splits and cracks as well, but these can all add to the charm of the piece. Think of it as stretching a rubber band across two finger tips to form a triangle, and hold it there. The stresses are in balance until something gives. If the muscles in your fingers relax or if the band snaps, then stresses are released and the triangular shape breaks down, just like our piece of burr.
There are two principle ways of coping with the burr’s tendency to distort, the first is to season the timber carefully then work with dry wood in the knowledge that further distortion will be minimal. The second method is to work with the timber in its green, freshly sawn state and to prepare for the inevitable movement that will take place.
Starting with the fully seasoned burr; I save these for pieces which tend to be display pieces in the shop or at a gallery. I have just finished working such a piece of oak burr which was very dry, hard and which yielded lots of dust. The burr has been part of dead oak tree which had fallen and lain on the ground for years. the surface of the burr had weathered spectacularly, adding to the organic feel of the timber by producing lots of small fissures in the timer, as well as some slight discolouration where decay had just started to set in. The resultant bowl is a beauty!
One of my earlier bowls turned in this way was a spectacular piece of sycamore burr which yielded a deep pot with an enclosed opening. The shape was dictated by the features of the burr and I carefully cut the wood so as to retain the best of them.
When working burrs from green timber, I usually work in close collaboration with a client for whom the bowl is to be a special commission, and my favourite such bowl was made in our first year at Pren, when a client called to commission something special for his partner. Having made quite sure that the client fully understood the rather random effects that drying out could cause, I sorted through my stock and found the perfect piece for him.
This piece of burr held its shape well whilst being turned, then began to show promising signs of adapting some interesting twists and turns as soon as it started to dry out, and we weren’t to be disappointed by it.
With the addition of accent features in leather and stone, this bowl had such an ancient, organic feel and it was just what the customer ordered.
So the next time that you see a large lump bulging out of the side of a tree trunk, just stop to imagine what could be inside it and, if it’s a dead tree on the ground, be sure to let me know!