Copper, or the bluish-green patina formed on copper by oxidation and known as verdigris, was common, as well as alum, a sulphate obtained from wood ash, chips of oak or alder wood. In order to fix and ‘brighten’ colours the favourites were burnt seaweed or kelp and lastly urine, which was readily available and collected by women in the mornings and left to grow stale to increase its strength and potency.
