Historically, glass has been etched with the corrosive and dangerous hydrofluoric acid, a combination of hydrogen and fluorine. Because of its reactivity, hydrofluoric acid must be stored in polyethylene or polytetrafluoroethylene containers. The acidic salt ammonium bifluoride has sometimes been formulated with other substances to form a "safer" etchant for glass. Unfortunately, this may lead to a false sense of security. Ammonium bifluoride is compounded with inert ingredients, and though not quite so strong as straight hydrofluoric acid, is capable of inflicting similar damage.
This reaction results in the removal of some of the silica from the surface of the glass object from the oxide matrix, leaving a roughened, frosted appearance. The reaction is not an overly rapid reaction, and so it is easily controlled to produce a useful artistic product. To assure that the etching occurs only where it is desired, wax or some other nonreactive substance is applied where acid etching is unwanted. Glass objects can then be Acid etched with a portrait, a landscape scene or some other artwork.
Acid etching, also known as 'French Embossing' is a process invented in the Victorian era. It gives a frosted, etched finish in delicate tones of white and diffused shades and is capable of producing very intricate patterns.
The process was originally used by the Victorians for decorating windows and doors in public houses and bars, where it gave a luxurious and expensive feel to sitting areas. It also afforded privacy as it is not easy to see through acid etched glass.
In a Victorian property the choice of etched glass or leaded lights was made by the developer of the block or street of houses. The entrance way normally indicates the choice and this style will be repeated in suitable windows in the rest of the building.
If the choice was etched glass, the best quality was often reserved for the front door and it's surrounding panels.
In the1860's acid etching and brilliant cutting started to be done on a semi industrial scale for the burgeoning house market. The invention of the large rotating stone wheel for the technique of 'brilliant cut' glass bore fruit in the very elaborate panels mostly seen in pubs. In the late 1870's craftsmen invented means of imitating acid etching more cheaply with sandblasting.
The acid-etching process gives generally better results with the cast/rolled glass being used for bulk and lower-priced work. Double-side etched glass and Mirror are the diffused reflection glass of choice for most bespoke framers, the leading brands being 'Inspiration NG' (Guardian Glass Industries). Single-side etching gives very good quality results for high-end framing but is more expensive to produce.
Examples are Reflection Control (by TruVue®) and Reflo (by Tegla). Cast/Rolled glass is mainly used for contract framing, photo frames etc.
Examples are Galleria (by Pilkington) and Glamatt (Glaverbel). Typically, diffused reflection glasses transmit 88-90% of visible light, reflect <8% and absorb 2-4%. UV filtration is similar to clear glass 45%)