Purpurin (Italian: Porporino; Latin: Haematinum, derived from Greek haimátinos = "of blood"; German: Hämatinon), sometimes referred to as glass porphyr, is an opaque glass of brownish to lustrous deep-reddish color which in classical antiquity was used for residential luxury objects, mosaics and various decorative purposes.
Pliny the Elder reports in his Historia naturalis: "Obsidian is made by artificial coloring and used for dishware, and also a completely red and opaque glass called haematinum.
[2] The process for "haematinum" (i.e., "blood-red ware") has not been related in any preserved documents from antiquity, and the details of its composition and production remained a mystery until the mid-19th century.
King Ludwig I of Bavaria, who intended to build a reconstruction of a Pompeian villa for educational purposes, assigned Max Joseph von Pettenkofer to the task of rediscovering the method of manufacturing the antique "blood glass", and indeed the young chemist reported success in 1853.
[5] His process called for fusing easily smelting standard alkali-lead glass with copper(II) oxide and magnetite in the presence of small amounts of magnesium oxide and carbon, followed by very slow cooling of the resultant brown mass, which would then take on a deep red color from precipitating microparticles of reduced metallic copper.