Pleats

Hello,

I am researching 1880s bustle gowns. Many of them have rows of tight pleats. Pleats that are still crisp and defined 120 years later. I saw one today a velvet bustle skirt that had long pleats the length of the skirt. I know the trick of using vinegar to hold pleats. That wouldn't work on velvet or hold the pleats for years. Does anyone know how the Victorians created these pleats?

Sincerely,
Shalie