Devitrification is the process of

crystallization Crystallization is a process that leads to solids with highly organized Atom, atoms or Molecule, molecules, i.e. a crystal. The ordered nature of a crystalline solid can be contrasted with amorphous solids in which atoms or molecules lack regu ...

in a formerly crystal-free (

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...

)

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

. The term is derived from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''vitreus'', meaning '' glassy'' and '' transparent''.

Devitrification in glass art

Devitrification occurs in

glass art Glass art refers to individual works of art that are substantially or wholly made of glass. It ranges in size from monumental works and installation pieces to wall hangings and windows, to works of art made in studios and factories, including gl ...

during the firing process of fused glass whereby the surface of the

develops a whitish scum, crazing, or wrinkles instead of a smooth glossy shine, as the

molecules A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry ...

in the glass change their structure into that of crystalline solids. While this condition is normally undesired, in

it is possible to use devitrification as a deliberate artistic technique. Causes of devitrification, commonly referred to as "devit", can include holding a high temperature for too long, which causes the nucleation of crystals. The presence of foreign residue such as dust on the surface of the glass or inside the kiln prior to firing can provide nucleation points where crystals can propagate easily. The chemical compositions of some types of glass can make them more vulnerable to devitrification than others, for example a high lime content can be factor in inducing this condition. In general opaque glass can devit easily as crystals are present in the glass to give its opaque appearance and thus the higher the chance it might devit. Techniques for avoiding devitrification include cleaning the glass surfaces of dust or unwanted residue, and allowing rapid cooling once the piece reaches the desired temperature, until the temperature approaches the annealing temperature. Devit spray can be purchased to apply to the surfaces of the glass pieces prior to firing which is supposed to help prevent devitrification, however there is disagreement over the long term effectiveness of this solution and whether it should be used as a substitute for proper firing techniques. Once devit has occurred, there are techniques that can be attempted to fix it, with varying degrees of success. One technique is to cover the surface with a sheet of clear glass and refiring. Since devitrification can change the COE somewhat, and devitrified glass tends to be somewhat harder to melt again, there is the possibility of this technique resulting in a less stable piece, however it has also been used effectively with full-fused pieces with no apparent problems. Applying devit spray and refiring can also be effective. Alternatively, sandblasting, acid bath, or polishing with a

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

stone or rotary brush can be used to remove the unwanted surface.

Devitrification in geology

In a general sense, any crystallization from a

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

could be considered devitrification, but the term is most commonly used for the formation of spherulites in otherwise glassy rocks such as

obsidian Obsidian ( ) is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Produced from felsic lava, obsidian is rich in the lighter element ...

. The process of conversion of glass material to crystallized material is known as devitrification. Spherulites are evidence of this process.

Perlite Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the Hydrate, hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. It is an indu ...

is due to hydration of glass causing expansion and not necessarily devitrification.

Glass wool

Devitrification can occur in glass wool used in high-temperature applications, resulting in the formation of potentially

carcinogenic A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and Biological agent, biologic agent ...

mineral powders.

References

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External links

Encyclopædia Britannica Online

Glass engineering and science Glass art Glass physics