Purpurin (glass)
Encyclopedia
Purpurin 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. Purpurin is somewhat harder than normal glass but can be easily cut and polished. Its red color is permanently lost upon smelting. The material bears some resemblance to goldstone
.
; Pompeii
is a prime example.
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." The art of making this type of glass seems to have originated in India; glass beads of a similar material have been found in the Indus valley and were dated to the late 2nd millennium BCE.
had found copper when he analyzed red glass from the Villa Jovis
, he mistakenly believed the fabled haematinon was not glass, but rather recast slag from copper smelting. In 1844, Schubarth made a strong case for it being copper-colorated glass - an opinion that should soon be proven correct.
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. 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.
Subsequently, Emanuel Kayser
realized the brownish tint was attributable to co-precipitated metallic lead
, and that this can be avoided by using borax
instead of lead glass or lead oxide. His recipe consisted of 60 parts silicon oxide in the form of pure quartz
sand, 10 parts calcined borax, 10 parts copper oxide, and 3 parts magnetite.
Classical antiquity
Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...
was used for residential luxury objects, mosaics and various decorative purposes. Purpurin is somewhat harder than normal glass but can be easily cut and polished. Its red color is permanently lost upon smelting. The material bears some resemblance to goldstone
Goldstone (gemstone)
Goldstone is a type of glittering glass made in a low-oxygen reducing atmosphere. The finished product can take a smooth polish and be carved into beads, figurines, or other artifacts suitable for semiprecious stone, and in fact goldstone is often mistaken for or misrepresented as a natural...
.
Historical references and archeology
Purpurin artifacts are frequently found during archeological excavations of more affluent Roman settlements, often along with actual Roman glassRoman glass
Roman glass objects have been recovered across the Roman Empire in domestic, industrial and funerary contexts. Glass was used primarily for the production of vessels, although mosaic tiles and window glass were also produced. Roman glass production developed from Hellenistic technical traditions,...
; Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...
is a prime example.
Pliny the Elder
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...
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." The art of making this type of glass seems to have originated in India; glass beads of a similar material have been found in the Indus valley and were dated to the late 2nd millennium BCE.
Rediscovering the technology
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. Although the German chemist Martin Heinrich KlaprothMartin Heinrich Klaproth
Martin Heinrich Klaproth was a German chemist.Klaproth was born in Wernigerode. During a large portion of his life he followed the profession of an apothecary...
had found copper when he analyzed red glass from the Villa Jovis
Villa Jovis
Villa Jovis is a Roman palace on Capri, southern Italy, built by emperor Tiberius who ruled from there between AD 27 and AD 37...
, he mistakenly believed the fabled haematinon was not glass, but rather recast slag from copper smelting. In 1844, Schubarth made a strong case for it being copper-colorated glass - an opinion that should soon be proven correct.
King Ludwig I of Bavaria
Ludwig I of Bavaria
Ludwig I was a German king of Bavaria from 1825 until the 1848 revolutions in the German states.-Crown prince:...
, who intended to build a reconstruction of a Pompeian villa for educational purposes, assigned Max Joseph von Pettenkofer
Max Joseph von Pettenkofer
Max Joseph von Pettenkofer , Bavarian chemist and hygienist, was born in Lichtenheim, near Neuburg an der Donau, now part of Weichering. He was a nephew of Franz Xaver Pettenkofer , who from 1823 was surgeon and apothecary to the Bavarian court and was the author of some chemical investigations on...
to the task of rediscovering the method of manufacturing the antique "blood glass," and indeed the young chemist reported success in 1853. His process called for fusing easily smelting standard alkali-lead glass with copper(II) oxide
Copper(II) oxide
Copper oxide or cupric oxide is the higher oxide of copper. As a mineral, it is known as tenorite.-Chemistry:It is a black solid with an ionic structure which melts above 1200 °C with some loss of oxygen...
and magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
in the presence of small amounts of magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
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.
Subsequently, Emanuel Kayser
Emanuel Kayser
Friedrich Heinrich Emanuel Kayser was a German geologist and palaeontologist, born at Königsberg.He was educated at Berlin, where he took his degree of Ph.D. in 1870. In 1882, he became professor of geology in the University of Marburg...
realized the brownish tint was attributable to co-precipitated metallic lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, and that this can be avoided by using borax
Borax
Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...
instead of lead glass or lead oxide. His recipe consisted of 60 parts silicon oxide in the form of pure quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
sand, 10 parts calcined borax, 10 parts copper oxide, and 3 parts magnetite.
External links
- Replication of the manufacturing technology (April 2002), with illustrations: Roman Glassmakers Newsletter No. 3 Archived