Blue blood is an English expression recorded since 1834 for noble birth or descent; it is a translation of the Spanish phrase sangre azul, which described the Spanish royal family and other high nobility who claimed to be 'pure', free of Moorish or Jewish blood, being of Visigothic descent. There is no connection between the phrase and the actual blood color of nobility; however, in the ancient agricultural societies of Europe the whole upper class had superficial veins that might be more visible and appear bluish by comparison to the rest of the pale-pinkish skin, as the skin itself was not tanned. In contrast with the working class of the time (mainly peasants), nobility and in general upper class people did not have to work outdoors, and mostly lived sheltered from the sun by dwellings and attire. The same contrast could be observed between untanned upper class Europeans - especially of northern stock whose skin tends to be less pigmented - and all social strata of Mediterranean populations with higher levels of genetically determined skin pigmentation. An alternative traditional explanation, argyria (a disease causing a blue-grey skin tone after digestion of silver), is considered less valid as table silverware was not massively and regularly used by much of the nobility.