“I am a museum interpreter at Bacon’s Castle in Surry, Virginia. We have a couple of window panes that have names, dates, and even a branch with leaves etched in them – all from the 19th century. Is it true that ladies would test their diamonds or other gems to see if they were real or glass by doing such etchings?”
You may have heard that a real diamond will scratch glass and an imitation one won’t. If only it were that easy! Many high quality imitation diamonds made in recent decades are harder than glass, so even fakes will scratch glass. Don’t rely on this myth to determine whether your own diamond-looking piece of jewelry is genuine or not. Take it to a reputable, local jewelry, one who has been in business for many years, and he or she will tell you at no cost whether it is genuine or not. They will not appraise it at no cost–for that you need an experienced CGA or Certified Gemologist Appraiser who has the training to judge your jewelry value it.
The idea that the ability to scratch glass proves a diamond’s genuine-ness is clearly a myth today. But what about in earlier times?
Well, it was closer to the truth in the past, when imitation diamonds were made of something called “paste.” Not the sort of paste you used in kindergarten to glue lace to your Valentine, this word meant a type of glass with a high lead content that was used to make imitation stones. According to the Encyclopedia Britannica, the Romans were the first to make this sort of imitation stone. For all you chemists, here’s the lowdown:
“Before 1940 most imitation gems were made from glass with a high lead content. Such glasses were called paste because the components of the mixture were mixed wet to ensure a thorough and even distribution. Colourless paste is commonly formulated from 300 parts of silica (silicon dioxide, SiO2), 470 of red lead (a lead oxide, Pb3O4), 163 of potassium carbonate (K2CO3), 22 of borax (a sodium borate, Na2B4O7·10H2O), and 1 of white arsenic (arsenic oxide, As2O3). Pigments may be added to give the paste any desired colour: chromium compounds for red or green, cobalt for blue, gold for red, iron for yellow to green, manganese for purple, and selenium for red.”
Nonetheless, that doesn’t mean it was true in the past–other clear stones that look like diamonds can scratch glass. Quartz, for instance. I think it likely that people who scratched on window glass were indulging in some playful or sentimental graffiti rather than testing their diamonds.
Some window glass in the Virginia Governor’s Mansion had two little girls’ names etched in it–these were youngsters who lived in the mansion when their father was governor in the 1840s. (Sadly, that pane went missing during the 1999 renovations.) Many old houses have windows with initials, names, dates, or even sketches that were scratched in the glass. My theory is that most of them were done by girls or young women having fun, but I can’t prove that.
Does anyone else work at places where someone etched something into the window glass?