White "stuff" on jewelry.

 Because of the “white stuff” (not the usual “green stuff”) on the metal beads of the purple and amber glass necklace, I Googled: white plague on silver jewelry.  This article mentions it and contains some new information about cleaning and storing jewelry. “This tarnish starts as a white residue on your jewelry that turns dark gray-blue after exposure to sunlight.” And, “Be careful about following silver-cleaning hacks. You may have read that lemon juice, lemon-lime soda, Coca-Cola, salty water, ketchup, vinegar, or even window cleaner will get tarnish off your silver jewelry. They might work at first, but they’re all acidic substances that will weaken your silver jewelry.” Over time, you’ll wind up with pitting and other problems. I’m happy to learn this, because it was recommended by a jeweler, I was going to buy some Windex. I will continue to “start with the most gentle method and then work my way through the others if needed.” I think thoroughly rinsing and drying after using any cleaning product is the most important thing to remember. Of course, the best thing to do is to store your jewelry properly and avoid exposure to harmful elements whenever possible. 

https://housewifehowtos.com/clean/how-to-clean-silver-jewelry/#:~:text=This%20tarnish%20starts%20as%20a,or%20while%20coloring%20your%20hair. Housewife How-Tos. How to Clean Silver Jewelry and Remove Tarnish.

First, the good news: silver tarnish doesn’t harm your jewelry. Some ornate, engraved pieces look better with a bit of tarnish since the dark brown or black layer emphasizes the design. But on other jewelry, it’s unsightly. And here’s more good news: using a few common household ingredients, you can get tarnish off your jewelry without causing damage.

   Tarnish is a chemical reaction between your silver jewelry and various substances. Thanks to the wide variety of things that cause it, it’s almost unavoidable. Things we come in contact with every day can tarnish silver — even the air! But did you know that even the foods you eat can cause tarnish, too? That’s because the compounds in some foods come out in your sweat, and those compounds can react with silver to produce tarnish.

   Silver sulfide creates a black tarnish on your silver rings or other jewelry. This reaction happens when silver is exposed to sulfur in cleaning products and cosmetics. Well-water (or bore water) is often sulfuric, too, and it’s also present in some foods like eggs, cruciferous vegetables (cabbage, broccoli, kale), and alliums (onions, garlic). If you eat a lot of sulfuric foods, your sweat can cause this reaction. Even the air can be high in sulfur, especially in heavily polluted areas.

Silver and Chlorine Result in Silver Chloride. This tarnish starts as a white residue on your jewelry that turns dark gray-blue after exposure to sunlight. Silver chloride tarnish often develops if you wear your silver jewelry while swimming in a pool or the ocean, when using certain cleaning and laundry products, or while coloring your hair. A diet high in chloride food (like rye bread, celery, olives, seaweed, or anything heavily seasoned with table salt) can make your sweat cause tarnish.

Copper in Sterling Silver Oxidizes. A dark greenish-black tarnish on sterling silver jewelry is due to its copper content. When copper is exposed to oxygen, it oxidizes. Since you can’t live without air, there’s no way to avoid this type of tarnish. You can clean it away, though.

Be careful about following silver-cleaning hacks. You may have read that lemon juice, lemon-lime soda, Coca-Cola, salty water, ketchup, vinegar, or even window cleaner will get tarnish off your silver jewelry. They might work at first, but they’re all acidic substances that will weaken your silver jewelry. Over time, you’ll wind up with pitting and other problems.