Sweet Chestnut's sapwood is narrow, distinct from the heartwood which is yellowish-brown in colour, closely resembling oak in appearance, but lacking the silver-grain figure characteristic of that timber, resulting from the finer rays. European Sweet Chestnut is a stable, straight grained and hard-wearing timber species (when the sapwood is excluded).The grain may be straight, but is more commonly spiral, particularly in timber from old trees, while logs are liable to cup and ring-shake. It weighs about 560 kg/m³ when dried. On account of its somewhat acidic character chestnut tends to accelerate the corrosion of metals, particularly when moist. It also contains tannin, as a result of which blue-black discolourations are prone to appear on the wood when it comes into contact with iron or iron compounds.