When Pompeii was rediscovered in 1748, archaeologists marveled at the detailed mosaics freed from the ash, scenes depicting Roman gods, gladiators and sea creatures.

What would post-apocalyptic explorers think should they come across the colorful murals adorning the fence behind Karen Lash’s house in D.C.’s Tenleytown neighborhood? Who lived here? What society gave rise to these images?

Will the murals even survive? Well, when it comes to longevity, the stone, glass and ceramic tiles that make up the Pompeian mosaics have nothing on the material in Karen’s murals: plastic. Plastic lasts forever, and the murals are composed of plastic bottle caps.

These are the caps and lids from soda bottles, orange juice bottles, Gatorade bottles; hummus, salsa and mozzarella tubs; peanut butter jars; yogurt cups. Karen has affixed them to her wooden fence to create four designs. There’s a sinuous sea serpent in a rainbow of hues, a sunburst, a “Tree of Life” and, fitting in this political town, a red-white-and-blue exhortation to “VOTE!”

The medium is the message. And Karen’s message is: There’s way too much plastic out there. Running along the top of the fence is information about the avalanche of plastic that’s swamping the land and filling the seas.

In her day job, Karen, 59, runs a program at American University’s School of Public Affairs that educates policymakers about legal aid. In summer 2019, she happened to hear an NPR report about how plastic has been found in the deepest, darkest recesses of the ocean. Then she read a Consumer Reports story about how food packaging sheds microplastics that we ingest.

Said Karen: “Have you ever had the experience where you learn something, and it just pulls the curtain back and you can’t unsee it? You can’t go back to seeing things the same way again. It just changes you.”

For Karen, that meant scouring the house she shares with her wife, looking for ways to reduce single-use plastics. Could they buy in bulk things that they had been buying in smaller packages? Was there ever a need to buy bottled water? Who needs plastic carryout cutlery? Doesn’t everyone have at least one metal fork at home?

“I was now seeing plastic everywhere in our kitchen,” Karen said.

Karen learned that plastic recycling is a bit of a joke. She knew that even if a bottle is recyclable, its cap often isn’t. Karen was struck by these tiny discs that come in myriad shapes, sizes and colors, like so many Roman tesserae. With her nephew, she sketched out a design and then used a power drill to make holes in the plastic caps and screw them onto the fence.

“I was totally hooked, especially because of two other things that happened very quickly,” Karen said. “One was that the children in our neighborhood who play in the alley were really into it. I had a lot of fun teaching all these little girls how to use a power drill. And I realized with every one of these young assistants I was able to have a conversation about what was motivating me and about the plastic pollution problem.”

The alley is not only a home for trash cans, but also a place to walk a dog, spin on a scooter, practice free throws, learn to ride a bike. And now this alley off 45th Street NW is a three-dimensional teachable moment.

Karen propped an old (plastic) beach bucket near the fence and neighbors started filling it with their own caps, raw material for Karen’s evolving creations. (She doesn’t need any more caps, thank you. Like the planet itself, Karen is awash in plastic.)

The project started before the pandemic, but Karen said it’s been a welcome distraction from the angst of the novel coronavirus. “It’s really the opportunity to focus on a problem like: Does that red really look good next to that purple? Do I need a smaller bottle cap to make that work? It’s a wonderful way to reduce stress.”

On a recent afternoon, twin sisters Claire and Anna Yoder, 12, were strolling through the alley with their mother, Shelley Vanneman. The girls have worked on the murals with Karen, picking out caps of their favorite colors — purple for Claire, pink for Anna — and finding just the right spot for them to go. They’ve taken the message home: Use less plastic!

From tiny acorns do mighty oaks grow — if, that is, we can clear the plastic away so there’s room for the seeds to take root.

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/john-kelly.