The Wondrous Glass

Pliny speaks of glass mirrors on several occasions.

In one instance he is very explicit on the subject:
Silver mirrors have come to be preferred [to bronze ones]; they were first made by Pasiteles in the period of Pompey the Great [106-48 B.C.]. But it has recently come to be believed that a more reliable reflection is given by applying a layer of gold to the back of glass.(Natural HIstory XXXIII.45.)

By the seventh century, glass seems entirely to have usurped the place of metal for mirrors. At least, Isidore of Seville tells us that "no other material is more fitting for mirrors . . ." (Etymologies XVI.16.)

Whether the mirror in the Villa of the Mysteries is a very early glass one, or whether it is an unusual silver one, its powers of reflection transcend the ordinary and venture off into a zone of allegory which we on the outside looking in are not yet equipped to comprehend.

As we attempt to understand the sometimes enigmatic world of Rome, glass certainly acts as a mirror on its art, its poetry, its observations of nature, its cults and social morés, and its networks of trade and diplomacy. The images we perceive are of a complex, many-faceted society.

And this is as it should be--for these images reflect back upon the complexities and antitheses inherent in glass itself. Even the derivation of the Latin work for glass -- "vitrum" has been much disputed by etymologists beginning with Isidore.

He tells us:
It is called glass [vitrum] because it is, with its clearness, transparent to the vision [visus]. For in other materials whatever is contained inside is hidden, whereas in glass whatever clearness or appearance is manifested on the outside,

it is the same inside, and though enclosed in a certain manner, is manifest.(Etymologies XVI.16)Thus, according to Isidore, "vitrum" comes from "videre" -- meaning "to see." Later etymologists have suggested other ideas on the subject.

One proposes the Sanskrit "vithura" -- meaning "fragile, brittle, breakable thing." Another proposes a derivation from the Latin "virere" -- meaning "to be green." Still another proposes a descent from the Sanskrit "vitrás" or "vétás" -- meaning "white, light, shining."

And so it is that wondrous glass means many things.

Images Associated with Glass

The imagery associated with glass in the other poems by Horace is sometimes evocative of darker thoughts.

"Indiscreet trust" is "as clear as glass and ready-charged with secrets to repeat" in Ode 18 of Book I.
Circe, in contrast to the faithful Penelope, is "like glass" in Ode 17 of Book I.

So too, in the visual imagery of Roman art there is a darker side to the portrayal of one quality of glass, at any rate:

Its quality of reflection.

In every culture, mirrors are laden with associations of deep psycho-social significance. Rome was certainly no exception.

A mirror could be any reflecting surface.
In the Pompeiian wall paintings, imagery of reflection seems always to be of a foreboding kind:

Narcissus with his face reflected in the dark pool of water.
Thetis reflected pensively in the gleaming shield of Achilles.
The enigmatic scene of a woman in the Villa of the Mysteries whose image is reflected in a hand mirror.

This last scene is puzzling on two counts. The image we are shown in the mirror is not the proper image that would be depicted if the painter's aim had been to show a rendition of actuality. Rather, we see a strange scene in which the standing companion looks down into the mirror; and in the mirror she sees the same view of the seated woman that we see from outside the picture.



Furthermore, the form of the mirror is unusual, and perhaps unique. It must be either of silver or glass set into a folding, square "compact."

Diatretum Technique

The tour de force of Roman glass-making was the diatretum

The tour de force of Roman glass-making was the diatretum technique, whereby a blank vessel was cut back to reveal a complex design connected only by narrow reserve struts to the remaining solid wall.

One type of diatretum found almost exclusively in the Rhineland was the cage cup variety carved as a lace network around the exterior of the vessel. Figural diatreta such as the famous Lycurgus Cup have a wider distribution. One, depicting the Lighthouse of Alexandria, was found in a hoard of treasures at Begram, near modern Kabul in Afghanistan.

These figural diatreta are understandably rare. After Roman times, the technique of diatretum carving in either mode was not attempted again until the nineteenth century when deliberate imitations of the Roman cage cups were made in Bavaria.

The extraordinary delicacy of the Roman diatretum vessels suggests the possibility that they were created on a special commission basis -- the glass-carver traveling with the blank vessel to the place where the commission originated. It is difficult to imagine how the Lighthouse diatretum could possible have arrived at Begram intact had it been carved before the arduous journey from Rome or Alexandria.

So delicate and specialized was the carving process that a law was formulated to deal with the contingencies of liability for a faulty product, depending upon whether the blank vessel was inherently flawed or whether the glass-carver's ineptitude alone was responsible for a ruined effort.

Roman Glass-making

Fragment of a Partho-
Sasanian faceted bowl

Greenish glass now devitrified and opaque
D. 10.5 cm
Second century AD
Seleucia (UM excavations)
KM 36358

Whole vessels of forms similar to our fragment excavated at Seleucia have been found in Japan. One was buried with the Emperor Ankan in A.D. 535. Unlike the devitrified examples found in the Middle East, the cut-glass vessels exported to Japan are still in pristine condition--their facets dazzling like so many mirrors.

To date, no actual examples of such western ware have been found in China; but on a painted silk banner from the Buddhist caves at Tun Huang, a Boddhisatva holds one of these Partho-Sasanian faceted bowls so that his hand is visible through the sparkling pale green glass. Thus, this striking portrayal vividly documents the presence of western glass at a remote outpost along the Central Asian Silk Route.

Further evidence of the Chinese interest in glass from the world of Rome comes in the form of lyrical poems composed by the nobility in praise of such luxury vessels which had ". . . braved the perils of the desert's limitless wastes, / And crossed the towering, precipitous Pamirs" in order to grace their tables:

Despite the vernal splendor of its hue,
Its clarity surpasses the purest winter ice.
There vessels are produced as though ceramic,
And their rare foreign shapes richly embellished.

Drinking Cups

From left to right:
(A) Carinated Beaker: On base ring; Colorless glass with trail at neck; H. 9.0 cm; Second or third century AD; Cyprus (Cesnola Collection; KM 88838
(B) Tall beaker: Colorless glass indented; H. 11.5 cm; Second or third century AD; probably Syria (Havemeyer Collection); KM 88845
(C) Beaker: Blue glass with wheel cut rings; H. 7.0 cm; Cologn (Kelsey Collection); KM 1669



U-shaped wine glass
Greenish glass
Spiral threading on upper half of the body
H. 9.3 cm
Fourth or fifth century AD
Karanis (UM excavations)
KM 5965





Modiolus (one-handed beaker)
Greenish glass with milky weathering
Wheel-cut rings
Blue trail on handle and ringing base
H. 14.8
Late first century AD
Egypt (Tano Collection)
KM 25729

Roman 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, initially concentrating on the production of intensely coloured cast glass vessels. However, during the first century AD the industry underwent rapid technical growth that saw the introduction of glass blowing and the dominance of colourless or ‘aqua’ glasses.

Production of raw glass was undertaken in geographically separate locations to the working of glass into finished vessels, and by the end of the first century AD large scale manufacturing resulted in the establishment of glass as a commonly available material in the Roman world.

Moldavite

Moldavite is an olive-green or dull greenish vitreous substance possibly formed by a meteorite impact. It is one kind of tektite.

It was named by A. Dufrnoy from Moldauthein (Týn nad Vltavou) in Bohemia, where it occurs. It is sometimes cut and polished as an ornamental stone under the name of pseudo-chrysolite.

Its bottle-green glass color led to its being commonly called Bouteillen-stein, and at one time it was regarded as an artificial product, but this view is opposed to the fact that no remains of glassworks are found in the neighborhood of its occurrence; moreover, pieces of the substance are widely distributed in Tertiary and early Pleistocene deposits in Bohemia and Moravia.

For a long time, it was generally believed to be a variety of obsidian, but its difficult fusibility and its chemical composition are rather against its volcanic origin.

Powder Glass

Pure silica (SiO2) has a "glass melting point"— at a viscosity of 10 Pa·s (100 P)— of over 2300 °C (4200 °F). While pure silica can be made into glass for special applications, other substances are added to common glass to simplify processing.

One is sodium carbonate (Na2CO3), which lowers the melting point to about 1500 °C (2700 °F) in soda-lime glass; "soda" refers to the original source of sodium carbonate in the soda ash obtained from certain plants.

However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide are added to provide for a better chemical durability.

The resulting glass contains about 70 to 74 percent silica by weight and is called a soda-lime glass. Soda-lime glasses account for about 90 percent of manufactured glass.

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.

As the term is used by geologists, sand particles range in diameter from 0.0625 (or 1⁄16 mm, or 62.5 micrometers) to 2 millimeters. An individual particle in this range size is termed a sand grain. The next smaller size class in geology is silt: particles smaller than 0.0625 mm down to 0.004 mm in diameter.

The next larger size class above sand is gravel, with particles ranging from 2 mm up to 64 mm . Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour).

ISO 14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In USA, sand is commonly divided into five sub-categories based on size: very fine sand (1/16 - 1/8 mm diameter), fine sand (1/8 mm - 1/4 mm), medium sand (1/4 mm - 1/2 mm), coarse sand (1/2 mm - 1 mm), and very coarse sand (1 mm - 2 mm).

These sizes are based on the Krumbein phi scale, where size in Φ = -log base 2 of size in mm. On this scale, for sand the value of Φ varies from -1 to +4, with the divisions between sub-categories at whole numbers.

The Atomic Structure of Glass

The atomic structure of glass shares characteristics of the structure in a supercooled liquid, glass tends to behave as a solid below its glass transition temperature.
A supercooled liquid behaves as a liquid, but it is below the freezing point of the material, and will crystallize almost instantly if a crystal is added as a core.
The change in heat capacity at a glass transition and a melting transition of comparable materials are typically of the same order of magnitude, indicating that the change in active degrees of freedom is comparable as well.
Both in a glass and in a crystal it is mostly only the vibrational degrees of freedom that remain active, whereas rotational and translational motion becomes impossible, explaining why glasses and crystalline materials are hard.

Glass verification experiment

New chemical glass compositions or new treatment techniques can be initially investigated in small-scale laboratory experiments. The raw materials for laboratory-scale glass melts are often different from those used in mass production because the cost factor has a low priority.

In the laboratory mostly pure chemicals are used. Care must be taken that the raw materials have not reacted with moisture or other chemicals in the environment (such as alkali oxides and hydroxides, alkaline earth oxides and hydroxides, or boron oxide), or that the impurities are quantified (loss on ignition).

Radioactive waste is a waste product containing radioactive material. It is usually the product of a nuclear process such as nuclear fission. However, industries not directly connected to the nuclear industry may produce quantities of radioactive waste.

The majority of radioactive waste is "low-level waste", meaning it contains low levels of radioactivity per mass or volume. This type of waste often consists of used protective clothing, which is only lightly contaminated but still dangerous in case of radioactive contamination of a human body through ingestion, inhalation, absorption, or injection.

Glass

Glass, an amorphous substance made primarily of silica fused at high temperatures with borates or phosphates. Glass is also found in nature, as the volcanic material obsidian and as the enigmatic objects known as tektites . It is neither a solid nor a liquid but exists in a vitreous, or glassy, state in which molecular units have disordered arrangement but sufficient cohesion to produce mechanical rigidity.

Glass is cooled to a rigid state without the occurrence of crystallization; heat can reconvert glass to a liquid form. Usually transparent, glass can also be translucent or opaque. Color varies with the ingredients of the batch.

Glass generally refers to hard, brittle, transparent material, such as those used for windows, many bottles, or eyewear. Examples of such materials include, but are not limited to, soda-lime glass, borosilicate glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride.

In the technical sense, glass is an inorganic product of fusion which has been cooled through the glass transition to a rigid condition without crystallizing. Many glasses contain silica as their main component and glass former

Glass plays an essential role in science and industry. The optical and physical properties of glass make it suitable for applications such as flat glass, container glass, optics and optoelectronics material, laboratory equipment, thermal insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber reinforced concrete), and art.

Decorative Techniques of Roman Glass

When a glass vessel is being blown, and thus is still in its heated state, its surface form as well as its shape can be manipulated in many ways.

In Roman times glassmakers took full advantage of the decorative potentials of their medium. A major by-product of the invention of blowing was the invention of mold-blowing. Here, a molten gather of glass was blown directly into a mold of two or more sides.

Using this technique, thin-walled vessels with complex figural or geometric patterns (sometimes including inscriptions) could be created repeatedly and quickly. The logo of the glass-maker Ennion frequently appears as part of the decorative scheme on his mold-blown vessels: "Ennion made me. Let the buyer remember him!"

Through mold-blown inscriptions such as these we glimpse something of the glass-makers themselves. Regrettably, however, inscriptions of glass-makers on objects other than their products are very rare. For all the interest taken by Roman authors in the qualities of glass, allusions to the people who created it are few and far between.

One curious story passed down from Pliny to Isidore of Seville describes the fate of a glass-maker at the court of Tiberius (A.D. 14-37). The craftsman demonstrated to Caesar that he had invented a means of tempering glass so that it would not break when dropped but could be hammered back into shape like a bronze vessel.

When the man admitted that he alone knew of this new treatment for glass, Tiberius had him beheaded "lest when this became known, gold would be valued like mud, and the values of all metals be debased." To what could this tale possible refer? It is tempting to postulate that it has something (however obscure) to do with the invention of mold-blowing.

If not the actual inventor of mold-blowing, Ennion was certainly one of the very earliest masters of the technique. An Ennion-signed cup found at Corinth in Greece in a sealed deposit together with a coin of A.D. 37-41 now provides us with a firm date for the early range of his career. It dovetails nearly with the setting of this peculiar story in the reign of Tiberius.

A Blown Glass Chandelier

In 2000, Chihuly's commission from the Victoria and Albert Museum for a 30 ft (9.1 m) high, blown glass chandelier dominates the museum's main entrance.

Dale Chihuly (b. September 20, 1941 in Tacoma, Washington, United States) is an American glass sculptor and entrepreneur. In 1967, he received a Master of Science in sculpture from the University of Wisconsin-Madison, where he studied under Harvey Littleton. In 1968, he studied glass in Venice on a Fulbright Fellowship and received a Master of Fine Arts at the Rhode Island School of Design. In 1971, with the support of John Hauberg and Anne Gould Hauberg, Chihuly founded the Pilchuck Glass School near Stanwood, Washington.

Chihuly maintains two retail stores in partnership with MGM Mirage. One is located at the Bellagio in Las Vegas, the other at the MGM Grand Casino in Macau

Glass Making

Archaeological evidence for glass making during the Roman period is scarce, but by drawing comparisons with the later Islamic and Byzantine periods, it is clear that glass making was a significant industry. By the end of the Roman period glass was being produced in large quantities contained in tanks situated inside highly specialised furnaces, as the 8 tonne glass slab recovered from Bet She-arim illustrates.

These workshops could produce many tonnes of raw glass in a single furnace firing, and although this firing might have taken weeks, a single primary workshop could potentially supply multiple secondary glass working sites. It is therefore thought that raw glass production was centred around a relatively small number of workshops, where glass was produced on a large scale and then broken into chunks.

There is only limited evidence for local glass making, and only in context of window glass. The development of this large scale industry is not fully understood, but Pliny's Natural History (36, 194), in addition to evidence for the first use of molten glass in the mid first century AD, indicates that furnace technologies experienced marked development during the early to mid first century AD, in tandem with the expansion of glass production.

The siting of glass making workshops was governed by three primary factors; the availability of fuel which was needed in large quantites, sources of sand which represented the major constituent of the glass, and natron to act as a flux. Roman glass relied on natron from Wadi El Natrun, and as a result it is thought that glass making workshops during the Roman period may have been confined to near-coastal regions of the eastern Mediterranean. This facilitated the trade in the raw colourless or naturally coloured glass which they produced, which reached glass working sites across the Roman empire.

The scarcity of archaeological evidence for Roman glass making facilities has resulted in the use of chemical compositions as evidence for production models, as the division of production indicates that any variation is related to differences in raw glass making. However, the Roman reliance on natron from Wadi El Natrun as a flux, has resulted in a largely homogenous composition in the majority of Roman glasses.

Despite the publication of major analyses, comparisons of chemical analyses produced by different analytical methods have only recently been attempted, and although there is some variation in Roman glass compositions, meaningful compositional groups have been difficult to establish for this period.