I guess I should have defined "cold". In a warm room the glass ones might still feel a little cool to our cheeks with our body temperature a factor, but my real pearls will still feel much colder in comparison. At least the older ones. Some of the newer freshwater that I know are real, they just don't feel as cold. Granted the coldness will not last long, ten seconds or so at the max before they start to warm up. Or maybe I'm crazy. Same test I run potential gemstones through in public, I press them to my face for a second. Real or manmade gemstones will be cold even in a warm room, fine glass or crystal rhinestones will not. That one has never failed me, and until lately neither had the pearl test. Often I don't have a loupe with me, certainly don't want to put a strange pearl in my mouth especially in flu season, and I am just not convinced the rubbing two pearls together works for me, I tried that on some of mine recently and got nothing. The person who first told me to use the cold test (granted only as a first test) was a Gia certified gemologist with pearl certification, she is the one that used to help me identify many of my gemstones and pearl items until she retired from doing shows in Nashville.
