A Fortnite player wondered why there was 'mold' in their game: turns out it's a texture Tim Sweeney added to Unreal Engine in 1995

There's a growing field that I like to call 'digital archeology': the excavation and analysis of weird artifacts that have become buried in decades-old software or only exist on archived websites. Sometimes those artifacts just rise to the surface on their own, as was the case with an image of "mold" spotted by a Fortnite player in the game's news feed.

It isn't a picture of mold, but a stock photo of "cave pearls, a kind of calcium carbonate deposit that forms in limestone caves," Epic Games founder and CEO Tim Sweeney said on X in response to the question from M1das.

Sweeney says he added the texture to the first version of Unreal Engine all the way back in 1995.

"This is Unreal Engine's default texture," he said. "I imported it into Unreal Engine 1 in 1995 while I was developing on a 90 MHz Pentium. It's still there and shows up when a programmer forgets to specify a texture."

I assume I must have seen these cave pearls many times: I've played a lot of Unreal Engine games, and whoever messed up Fortnite's news feed is hardly the first developer to ever forget a texture. But I don't recognize the image. Not like the Source engine's missing texture icon, that famous fuchsia checkerboard, or its giant red "ERROR" text.

Maybe Unreal's default texture just evaded my long term memory by being so ambiguous: blobs of an organic-looking something. It hasn't evaded the subconscious minds of Unreal developers, though. "This image haunts my dreams," said an ILM Immersive artist last year.