Paper marbling is alive and well at Oberlin College's Letterpress Studio. Alex Fox filmed his friend Jones Pitsker demonstrating a couple of techniques.
Here's a lovely feather pattern:
Jones has an Etsy shop called AmericanMarble if you'd like to see more or want to commission something. And here's a vintage film Rob found last year if you want to see more.
• Jones Pitsker: Bouquet Marble Pattern (YouTube / Alex Fox)