Mika's kuksa had been made near Raudanjoki (which means 'iron river') in the middle of Finnish Lapland.
He described to me how a traditional kuksa is made from a burr (or 'burl' in the US) of birch (Betula sp.) that has grown in the far north of Scandinavia. Birch timber has no strong taste and is not toxic. These northern trees also grow more slowly and have denser timber than their more southerly-growing relatives, which makes them ideal to use.
A burr is a rounded growth caused by the tree dealing with an irritant or disease. It would be detached from the rest of the tree and then peeled to reveal the timber, which is then shaped using knives to create the kuksa. The rounded shape of the burr means that the grain travels in a curve around the bowl of the vessel, so it is stronger. The dots of dormant buds held in the grain pattern of the burr also help, as they break up the grain to reduce lines of weakness in the kuksa's bowl and so prevent damage to it.