Before Play-Doh became one of the world’s most recognizable children’s toys, it was something completely different: a wallpaper cleaner.

In the 1930s, Cincinnati-based Kutol Products produced a soft, dough-like compound designed to remove soot and coal residue from wallpaper. At the time, coal-burning heaters could leave walls covered in grime, making the unusual cleaning product surprisingly useful.

Then technology nearly killed the business.

As households switched from coal heating to cleaner fuels such as natural gas, there was far less soot on people’s walls. Kutol’s wallpaper-cleaner sales collapsed, putting the company in serious financial trouble.

The unlikely rescue came from Kay Zufall, a nursery-school teacher and relative of Kutol’s owner. After learning that the compound could be used as an art material, she brought some into her classroom.

The children loved it.

Zufall realized that the product’s future might not be on walls at all—it could be in children’s hands.

Kutol eventually removed the cleaning ingredients, added color and fragrance, and introduced the product as Play-Doh in 1956. The exact “$1 billion mistake” framing is more of a catchy modern description than a historical valuation, but the transformation itself is real.

A product created to clean dirty walls ended up helping generations of children create almost anything they could imagine.