Greenwood After Care, Seasoning

In this greenwood carving aftercare series we covered abraiding and burnishing last time and in this weeks blog we will be looking at how to allow our projects to dry out after carving them in greenwood, commonly referred to as seasoning. After this process we can then look at applying a finish which can help protect it and enhance its aesthetic qualities in the next blog in this series.

We need to take care with seasoning because if our projects dry out in a way that causes stress in the wood it will lead to either cracking, warping or both, and after spending lots of time, energy and effort releasing our green wood creation from your log, this is the last thing we want to happen and it can be very frustrating if it does, so lets see what can be done to help prevent it.

The amount of moisture in the wood and the time taken to season varies through many varied factors. It will change from species to species, time of year harvested, if the bark is on or off, if it is split, the size and length it is, how it is stored and environmental factors

An example of some of the differences in the moisture content of greenwood can be seen between green oak which can have a moisture content between 70-80% while ash which is renowned to have a very low moisture content can be 35%. This will also vary through the typical British seasons, being lower in the early spring, increasing as the sap rises through March and onwards prior to the bud burst.

To give you an idea on where we want to be with the moisture content of our carving creations, let us take a look at some examples that you can relate too. Firewood is a great way of doing this, greenwood generally makes for poor firewood because of all moisture it contains (ash being the exception due to its low moisture content). With all this moisture in the wood there are some key characteristic differences between it and seasoned wood, which holds a lot less moisture. Greenwood will feel cold to the touch compared to seasoned wood side by side in ambient temperatures, it will also feel a lot heavier than seasoned wood of the same species and size, and finally it will sound a lot duller than seasoned wood when struck compared to the ringing tone of seasoned wood.

We already understand the moisture levels in greenwood from two different species, so let’s now look at moisture levels within firewood to help us understand what is needed in seasoning our own greenwood projects. Most good firewood is seasoned with about 20% moisture content and wood seasoned outside will rarely go below 12%. Firewood recommendation for stoves is at 10-12% and the wood objects in your centrally heated home may be as low as 7-8%.

Your carving will achieve its own moisture level somewhere in this range (7-12%), where it will no longer lose any moisture and then becomes stable. Where this level is precisely will depend on its direct environment. Once it has fully seasoned and is no longer losing moisture it has reached what is known as its equilibrium. This is where it neither loses nor gains moisture. And this is where we are looking to be with our project prior to treating them if desired.

Whilst we are looking at seasoning it’s as well to be mindful of shrink rates of wood, as this can have a dramatic impact on our greenwood projects. As wood loses moisture it starts to shrink, it does this in three different directions and at three different rates. Firstly, along the grain, shrinking by 0.01%, secondly across the grain, shrinking by 10% and thirdly, radially shrinking by about 5%. So, when greenwood is left in the round the difference in shrink rates will create stress in the wood and cause it to split radially. We remove a lot of this stress when we split our greenwood rounds in half before we start to carve, intersecting with the pith (first ring of growth).

However, even when this is done, seasoning can still cause your carving to distort and sometimes split, again, caused by stress in the wood. This can happen when allowed to dry too quickly or with large temperature changes within a brief time. It is more prevalent with larger carved items like Kuksas, bowls, large ladles, dough bowls, as opposed to teaspoons, eating spoons, etc. With these larger items you can help minimise these effects leaving the thickness chunky and by helping to slow down the rate the moisture leaves your greenwood carving. This can be achieved by enclosing your carving in something breathable which you place in a cool spot, like in a paper bag with the open end rolled down and stored in the north corner of a shed or garage. This will help to stabilise the seasoning process and avoid these issues. It is however not a guarantee.

This can take a few weeks in the form of small spoons and butter knives, or a few months for lager utensils. As hinted above, I often leave large bowls and kuksas with a minimum of 10mm thickness on all surfaces to season slowly for 6 months or more, to reduce the risk of warping and cracking, before revisiting them after they are seasoned, to then carve down thinner to the desired final thickness. Personally, I have found this works really well for me.

After seasoning we may wish to concern ourselves with protecting our creation from the environment, from changes of humidity levels it may encounter during use. This is because wood is “hygroscopic.” This means that it can absorb and loose moisture from the air if the humidity levels change. As with the care we took in seasoning our carving when it was green, if your seasoned carving absorbs moisture and dries out in a way that causes stress in the wood it will again lead to either cracking, warping or both. This is where helping to seal off or reduce the effects of hygroscopic action from your carving can help. We will look at this further in the next blog in this series, starting with oils and baking, until then, happy seasoning.