Marble Roman emporers used to be dressed in porphyry togas because it is the colour of Roman Imperial Purple.
The first image of porphyry in this blog entry is not from an art image database but from a geological one which I found by searching The Culture Grid. If you are after images from Ethnography, Geology and other non art and design objects then have a look at the Culture Grid.
Culture Grid opens up a wealth of information from museums, galleries, libraries and archives: giving greater access to UK culture, arts and heritage. It contains approximately 3 million items from hundreds of collections on all topics.
University College London (UCL) and University of Reading have just added 6,500 images of objects from their museum collections to Culture Grid. The images can be freely viewed, downloaded and used under a Creative Commons licence.The objects include rare Ancient Egyptian artefacts brought to life in twenty-first-century 3D; digital images of zoological specimens in glass jars, strange and beautiful anatomical prints, sixteenth-century portraits, and intriguing nineteenth-century scientific gadgets.
Preserved infant lemur Grant Museum of Zoology UCL. Image from the Culture Grid