LUHANSK, Ukraine — THE microwave was a loaner, left for repairs by a family that fled last year’s shelling and never came back. With a few tweaks and the judicious use of a soup can, it had been weaponized, shooting microwave rays capable of blowing up a boombox.

Or, say, fry two eggs on a plate in a backyard experiment. That was what Kreosan, the do-it-yourself science duo with a cult following on YouTube, planned to do one chilly morning this spring. When the time came to flip the switch to power up the magnetron, Pavel Pavlov, 21, urged a reporter to step back.

“Whatever this does to the eggs, it can do to your eyes,” he said, and turned the dial of the disemboweled microwave to the max.

Mr. Pavlov and his partner, Aleksandr Kryukov, 32, are natives of Luhansk, a sprawling, industrial city of Soviet-era apartment blocks and coal-heated cottages that was seized by separatists and shelled last summer in the war between the Ukrainian Army and the rebel Luhansk People’s Republic. Then came months of blackout and economic blockade, and now a bleak future as a pariah state, cut off from Ukraine but not a part of Russia.