K5 OR K9 BOROSILICATE GLASS (“CHINESE CRYSTAL”)
This is the most common type of “crystal” that you’ll see out there. If the fixture itself was made in China, it is overwhelmingly likely that the crystal will be of this type. Borosilicate glass is not, strictly speaking, crystal, as its lead content is below 10% (the original terms “K5″ and K9″ refer to the percentage of lead oxide content — 5% and 9% respectively). K9 glass should be considered to be of a higher quality than K5 glass.
K9 glass is popular for a number of reasons: It is relatively cheap to make compared to real crystal; it has a relatively high refractive index and pretty good clarity properties. This type of glass can be polished as highly as crystal can be. Additionally, because most mass produced lighting worldwide is made in bulk in China, it makes sense that those fixtures would ship with K9 glass — an inexpensive option that is manufactured locally.
If you are buying a crystal chandelier or pendant for under, say, $1,500, the chances are that the crystals will be either K5 or K9 borosilicate glass. Consider K9 to be the Toyota Camry of chandelier glass: relatively cheap, reliable, ubiquitous — it gets the job done. But, given that your chandelier is the jewelry of your home, you may want to consider spending a little more to get something considerably more exquisite — something of heirloom quality that you’d be happy to pass down the generations. You may wish to opt for real jewelry instead of costume jewelry.
GEM-CUT CRYSTAL
Gem cut crystal generally refers to high quality, “real” crystal, between 24% and 34% lead oxide. There are gradations of quality points within this category, such as optical purity, and polish. Optical purity has to do with minimizing the distortion of light passing through, and the best way to do that is to control the cooling process of the molten crystal.
Once molten crystal is poured, it cools much like a cake fresh from the oven: The outer parts cool down first, and the innermost center cools last. With crystal, those temperature variations can cause tiny striations — kind of like fingerprints in the middle of the crystal. To prevent this, manufacturers have learned that they can apply heat to the cooling process so that the outer portions of the crystal cool at roughly the same rate as the core. Obviously, this can get a little tricky and adds to the manufacturing cost of the crystal.
Other variabilities in quality include the sharpness of the faceting and how highly polished the surface of the crystal is. Some manufacturers will include a semi-precious metal coating, which can protect the crystal’s polish. At Michael McHale Designs, our standard crystal is optically-pure, sharply faceted, and highly-polished.
Post time: Dec-04-2022