Porphyrogennetos

...touch through the colour

Porphýra, the Purple Chamber, a pavilion of the Great Palace of Constantinople): no child born anywhere else could legitimately be called Porphyrogénnētos. This pavilion was a free-standing building in the Great Palace complex in Constantinople. As the Porphyrogennētē Anna Komnena described it, the room rested on one of the Palace's many terraces, overlooking the Sea of Marmora and the Bosphorus Strait, "where the stone oxen and the lions stand" (i.e. the Boukoleon Palace), and was in the form of a perfect square from floor to ceiling, with the latter ending in a pyramid. Its walls, floor and ceiling were completely veneered with imperial porphyry, which was "generally of a purple colour throughout, but with white spots like sand sprinkled over it

//www.ancient-egypt.co.uk/people/Imperial%20Porphyry;%20its%20special%20qualities%20which%20influenced%20its%20form,%20function%20and%20use%20in%20antiquity.pdfThe 


mud-purple feeds on rotting slime and the seaweed-purple on seaweed, both being of a very common quality. A better kind is the reef-purple, collected on the reefs of the sea, though this also is lighter and softer as well. The pebble-purple is named after a pebble in the sea, and is remarkably suitable for purple dyes; and far the best for these is the melting-purple, that is, one fed on a varying kind of mud. Purples are taken in a sort of little lobster-pot of fine ply thrown into deep water. These contain bait, cockles that close with a snap, as we observe that mussels do. These when half-killed but put back into the sea gape greedily as they revive and attract the purples, which go for them with outstretched tongues. But the cockles when pricked by their spike shut up and nip the creatures nibbling them. So the purples hang suspended because of their greed and are lifted out of the water.

natural history IX

oxacan purpura dyeing - milking the shellfish

The official fasces and axes of Rome clear a path, and it also marks the honourable estate of boyhood; it distinguishes the senate from the knighthood, it is called in to secure the favour of the gods; and it adds radiance to every garment, while in a triumphal robe it is blended with gold. Consequently even the mad lust for the purple may be excused; but what is the cause of the prices paid for purple-shells, which have an unhealthy odour when used for dye and a gloomy tinge in their radiance resembling an angry sea?

http://www.masseiana.org/pliny.htm#BOOK%20IX

http://www.kremer-pigmente.com/media/files_public/36010e.pdf