You've definitely seen those old-fashioned Pyrex dishes somewhere. The brightly-hued containers, often decorated for floral motifs, can be found at yard sales, grandma's house or even your own kitchen cupboard.

But before you decide to donate or toss any of that outdated glassware, think twice!

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Vintage Pyrex has been selling for up to $1,800 online. Even single bowls are going for a whopping $900 and this "Foulard Pyrex mug" on Etsy is up for sale at $700.

Think you're sitting on a vintage Pyrex gold mine? Look out for opaque, brightly colored pieces that often feature floral and geometric designs.

Happy Frankenset Friday! Today's set is special because it contains the rare Golden Scroll 443 from @theskvintage. The set also includes Horizon Blue.

A post shared by JoRetro Vintage Market (@joretro) on

Classic Pyrex Primary Colors mixing bowl set and refrigerator dishes! I have fond memories of my mom's awesome potato salad being served in the yellow bowl! #recyclingretro #pyrexprimarycolors #pyrexforsale #pyrexjunkie

A post shared by kathy missal (@recyclingretro) on

Happy Fourth of July from #HobAndNail and our patriotic Pyrex 1.5 pint 401 mixing bowls for sale on #etsy at link in profile.

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Social media is flush with posts from Pyrex enthusiasts.

Vintage Pyrex collectors are currently sharing their glassware hauls, swaps and purchases on dozens of Pyrex Facebook groups. The hashtag #pyrexjunkie on Instagram reveals over 12,000 posts from the glassware aficionados. Between avid collectors and other home cooks, the century-old Pyrex brand is still beloved by many.

So why is this American dishware so coveted? Vintage Pyrex has been hailed for its durability and longevity. Once Pyrex changed its formula to soda-lime, instead of the arguably stronger borosilicate, discontinued vintage Pyrex made with the original glass formula became even more valuable.

Today, pieces made between 1915 and the late 1970s are sought out by thousands of Pyrex collectors. Vintage Pyrex is so special that it even made it into the Corning Museum of Glass.