How to Identify Crystal Doorknobs

Vintage glass doorknobs are like diamonds for doors. Many sparkling examples are available at antique malls, flea markets and salvage yards. However, not every glass doorknob is a crystal doorknob. Examine a find carefully to make sure it's crystal, not ordinary glass.

Things You'll Need

• Glass doorknob (clear or colored)
• Lead testing kit (optional)

Instructions

1. Pick up the doorknob and study its weight in your hand. According to "Antiques Roadshow Primer," basic glass is composed of silica (sand, flint or quartz) and soda or potash. Crystal, on the other hand, contains oxide of lead in place of soda (hence the name "lead crystal"). The addition of lead actually increases the weight of the glass. A crystal doorknob should have a substantial, hefty feel. A lightweight knob is probably not crystal. If the vendor has several glass doorknobs for sale, compare ones of similar size and shape. A heavier specimen might be your first clue that you've found crystal.

2. 

   Cut crystal has precise incisions.

   Examine the pattern on the doorknob (many are incised with pinwheels, diamonds and similar designs) and run your fingers over the surface. The edges on a cut crystal piece are sharp and precise. If the edges are dull or rough, the doorknob is pressed glass. If the doorknob is smooth, the surface should have a polished sheen without raised seams, which are mold marks and indicate pressed glass.

3. 

   True crystal has a clarity that unleaded glass can't duplicate.

   Hold the doorknob up to the light. Lead gives crystal exceptional clarity and brilliance, even in colored examples. An ordinary clear glass doorknob, on the other hand, will look murky (like peering through an ice cube) and may even have a gray or greenish cast. Colored glass doorknobs are dull as well. If the doorknob is patterned, a crystal version will refract light like a prism. If you see distinct rainbow reflections when you hold up a glass doorknob, it's crystal.

4. Try a lead testing kit if you still have doubts whether the doorknob is crystal. Naturally, you can't take one of these kits into a flea market or antique mall to test a doorknob before you buy. However, once you get your treasure home, you'll find a basic swab or wipe-on lead testing kit is ideal for your needs. You can get results quickly, and most kits are inexpensive (cost depends on the manufacturer and the amount of surface you can test with the kit). Lead testing kits are available from hardware stores and online retailers. (And, no, there is no danger from lead in a crystal doorknob since you're not using it with food or drink. The test kit is helpful, though, for scientifically confirming that a glass knob is crystal.)

Tips & Warnings

• All too often, vendors at flea markets and antique malls mark all clear glass as "crystal." Never trust a tag or label--judge for yourself.

• If you're shopping online for antique crystal doorknobs, it's hard to identify true crystal. By studying photos, you might be able to evaluate clarity and light refraction, perhaps even the sharpness of the cuts. However, ask plenty of questions to ensure that the knob is crystal, not ordinary glass. The Antique Doorknob Collectors of America website includes links to reputable salvage dealers who may have authentic vintage crystal doorknobs in stock.

• Contemporary crystal doorknobs are available as well, both as modern designs and antique reproductions, but buyer beware. Quality of materials is inconsistent. Make sure you are buying genuine crystal.

• Even if you determine a doorknob is crystal, also check for chips and cracks. Condition matters. A broken edge could cause injury, and a crack could make the doorknob unstable.

References

• "Antiques Roadshow Primer"; Carol Prisant; 1999
• American Cut Glass Association: American Brilliant Period Cut Glass, 1876 -- 1917
• GlassOnWeb: Crystal Glass
• InspectAPedia: Home Test Kit for Lead on Building Surfaces
• The Washington Post: Crystal Decanters Off-Limits

Resources

• Antique Doorknob Collectors of America
• This Old House: The Beauty of Glass Door Knobs