Design Aesthetics: Alabaster

Alabaster is one of the most popular materials used in residential lighting fixtures. Often, "alabaster" as a term means any glass or shade that's predominantly white, marbled with white veins and semi-transparent. There are two mineral types with the name "alabaster". In previous ages, calcite alabaster was used for sculptures and small, ornate carvings like perfume bottles. Presently, the most common form of alabaster is the gypsum variety. Many lighting fixtures, such as chandeliers, pendants and sconces feature ivory and white faux alabaster glass.

How do you prevent alabaster sconces from getting discolored?

Q. "We have 20-year-old genuine alabaster sconces that have a discolored spot on the outside of the alabaster ‘lenses’. Can this be safely removed? We used a soft sanding sponge, and a lot of the stain came out, but I’m worried about the long-term effects of sanding. I’m not sure if the spot is caused by the missing heat shields, which would have protected the insides of the sconces from the 60W lamps, or something else. The discoloration is not nearly as noticeable on the inside of the lenses. Thanks."

Randall Whitehead, IALD,
Professional Lighting Designer says:
This situation occurs quite often. What usually happens is people put in higher-wattage bulbs than what is recommended for the fixtures, and the alabaster closest to the bulbs gets “cooked.” In your case, the heat shield was removed or lost, and the unshielded heat from the 60W bulb caused the discoloration.

You were able to get a lot of the discoloration out by using a soft sanding sponge, but until the wattage is reduced or the heat shield is replaced, the dark spot will, in time, return. According to alabaster expert John Haddad of JH Lighting, the heat of the bulb has taken the moisture out of the stone, and that can’t be replaced after the damage has been done. To compound the issue, a sealant is normally applied to alabaster when a fixture is new, and you removed some of this sealant when you sanded the dark spot. This unprotected area will attract dirt over time and cause further discoloration. The dirt and dust in the air attaches itself to the exterior of the lens, which is probably why the dark area appears more on the outside, as opposed to the inside.

If at this point you have gotten enough of the discoloration out to live with the fixtures as they are, my suggestion is to use a dimmable screw-in CFL to reduce the heat. Good CFLs are manufactured by Maxlite and Earthtronics, among others. You can also consider replacing the alabaster, which is the more costly alternative.

More and more manufacturers of alabaster fixtures, like JH lighting and The Basic Source, are using the new GU24 technology to offer much of their line with CFLs that provide more light for less wattage and reduced heat output as compared with incandescent. Maxlite even offers a screw-in socket, called the MLGSM, that instantly and permanently changes an incandescent fixture into a GU24 fluorescent fixture without rewiring.
Source: www.ResidentialLighting.com