Bowls vs. splinters – which side of the wooden board should be on top?

When wood gets wet, it swells. Soaked boards tend to form bowls, i.e. they bend so that water can collect on them. To prevent this, the core side (right side) of the boards should face upwards or outwards. However, if the core side is ugly or if parts of the heartwood are already splintering off, then turn the board with the core downwards (right side down).