Tuesday, April 21, 2015

Sticks and dust and bugs and hot, hot water!

I've started using some spotted gum branches in my wall hangings. I've never used spotted gum before, and one thing I have noticed about it is that it can be a bit buggy. If there's one thing you don't want to see as a person working with timber, it's this:
This branch, which had been sitting on top of my workroom cupboard for a month or so, ejected the most wonderful pile of borer dust, and got me thinking. Specifically, "Oh no!"

Until recently, I've only ever been using casuarina or she-oak branches in my wall hangings. I harvest them green and allow them to dry naturally for many months before stripping off the bark, and I've never seen any sign whatsoever of insect infestation. Perhaps the casuarina is naturally repellant, but there's been no sawdust or telltale 'exit' holes.
Green-harvested casuarina sticks. Dried naturally.
Now that I no longer live close to a reliable source of casuarina (waaah!), I've been eyeing off the timber to be found locally - here on the shoulder of Mount Coot-tha in Brisbane, it's predominantly eucalyptus, and we've loads of trees in our garden, regularly shedding lovely sticks. I've been casting lots of plaster gumnuts lately, so it's a natural progression to start using gum branches - if only it weren't so full of borer! It seems that borers love spotted gum, and it doesn't seem to matter whether the timber is green or dry - it's all full of holes.

Now, I love the holes. I do. They tell a story and can leave some lovely markings on the surface of the timber. But it would be pretty poor form of me to pass on some hungry passengers in a work that someone may purchase from me... eeek!

Much research on woodworking forums ensued. It seems that the most reliable way of ensuring that any timber-munching critters (and their eggs) are dead is to heat treat the timber. Big mills do this in 'kilns' which, these days, are actually giant industrial microwaves. Some woodworkers rig up  wood-fired 'kilns' where the timber can be baked. Some bugs can be killed by freezing, although the northern hemisphere people scoff at that idea - for don't their bugs come back every year after being under ice for months? Some treat their wood using steam. Others swear by boiling - and this is the solution I'm going with. Just a few weeks ago, C said to me, "I'm going to sell my mum's old copper on Gumtree, unless you want it?" At that exact moment I was boiling up a test batch on our gas stove in my biggest and most expensive saucepan!

So, the copper has been fired up quite a few times since then. It's basically a very large electric coffee urn, and it fits loads of sticks in it at once!
The general gist of heat treating timber is that it needs to be kept at boiling temperature for at least an hour and a half. Super easy! And the smell... it's incredible. A steamy gummy tang (curiously, nothing like eucalyptus oil) whenever I open the lid. Afterwards, the water is stained a dark brown colour (from the tannins in the timber, I think) which I imagine could be used to dye something... I may try that in some future batch!

For my new gumnut wall hangings that I am working on (which use the thicker branches in the photo above) I then dunk the sticks in a mild bleach bath. After a soak, this gives them a lovely pale glowing quality that I'm really enjoying working with... stay tuned for an Etsy shop update in the coming weeks!
Incidentally, my gumnut stick bunches in my Etsy shop are now heat treated, too. Previously, I've found that these smaller sticks tend to break when I'm sanding them, if they have been weakened by having a borer munch through them. So, I've been able to weed any possible passengers out - the heat treating will doubly ensure that any critters are inactive!