The Pith rule is one of the few rules worth sticking to in green wood carving, though it can be broken by seasoning the wood first. I am more and more inclined to carve at least partially seasoned timber.With sharp tools, most woods are easy enough to carve when you get through the outer,most seasoned surface. If you carve a wood that is very wet ( think that cut in the spring or summer) it is all most impossible to get a finished cup in one session. You will need to let it dry a few days to get a good finish. The longer you let it dry( weeks or months), the more oil it will absorb. I often hear people ask about a white, or grey bloom on the surface of the cups. This is moisture trapped by an oil finish but on to soon,. I agree that Birch Burr is beautiful, possibly my favourite timber for cups but most timber is fine, I am surprised that we don't use more Willow ( still used in Eastern Europe). It follows that a wood that holds a lot of water will, if thoroughly dried, absorb oil well. I am very much looking forward to seeing the Sycamore Kuksa. A traditional wood for us Welsh despite the fact we are all removing it from our ancient woodlands.
A lot of timbers split, because the damage is already in the wood, due to clumsy processing.If you saw a log in two without supporting the two sections, the lower half of the split log might have the equivalent of stress fractures in it. When we select a branch that has been blown down, we often go for the section with the widest diameter. Invariably this is next to the traumatic break where the wood split as it broke. You might not see these checks and splits in wet wood , but they might well will open. The clumsy use of an axe, a blunt axe or the wrong type of axe often creates unseen problems, where the wood has been compressed or bludgeoned leaving unseen damage.
If your cup has cracks that radiate outwards from the centre of the front or rear wall, you probably have not removed enough of the wood either side of the pith and your cup is doomed. If the cracks are around the lip of the cup, this is often from traumatic harvesting or processing.The good news is that if you remove the damage, then rub some oil around the lip, it is unlikely to split again. In fact with difficult woods I often rough shape a cup, then oil the lip to prevent it splitting.
Nature of course does her own thing and cups will split for other reasons. At The Bushcraft Show, our birch cups were splitting as we could carved them . Wet wood on a hot sunny day.At the Wilderness Gathering, I was trying to carve some Silver Birch from Dorset. If I had not carved tons of Birch before, I might have never carved it again....it was impossible
To play safe I always roughly carve a cup then pop it in a paper bag for a few days. I don't think you need to put shaving in with it, they only delay thing more. The same applies to plastic bags, except they also often encourage mould.As my cups are for sale, I wouldn't want to risk mould in a cup, though 9 times out of 10, you can sand it away.
I reckon a paper bag or even one inside another bag keeps all sorts of trouble at bay.If I have run out of bags, fine cotton cloth does the job.
