Solid gold jewellery is exactly that, it's jewellery made with gold from surface to core and can come in 9, 14, 18, 22 or 24 karats. The carats are a measure of the golds purity. 9 karat means 9 parts pure gold / 15 parts alloy (alloy just means a mix of different metals). 14 karat is 14 parts pure gold / 10 parts alloy. Therefore, 24 karats is 100% pure gold. Pure gold is very very soft and not suitable in jewellery making, therefore the industry mixed alloys into the gold to make it stronger for the purposes of wearable jewellery.