Robert Oster Hippo Purple is a Robert Oster ink made exclusively for the launch of the Hippo Noto Notebook. I purchased a Hippo Noto notebook and a bottle of the ink from the Kickstarter campaign a year ago, but haven't gotten mine yet. Luckily, a pen friend brought a bottle to a Seattle-ish Pen Posse Meetup and let me steal a sample. You can find the ink online at hipponoto.com.
Hippo Purple is a medium purple-brown. It really does look like the color of hippos.
In large swabs, the ink turns black around the edges.
Let's take a look at how the ink behaves on fountain pen friendly papers: Rhodia, Tomoe River, and Leuchtturm.
Dry time: 15 seconds
Water resistance: Low
Show through: Medium
On 20 pound copy paper the ink behaved well, no issues that I noticed.
Ink swabs for comparison, left to right (top to bottom for mobile RSS): Diamine Merlot, Robert Oster Hippo Purple, and Diamine Tyrian Purple. Click here to see the Robert Oster inks together.
I used a broad Pelikan M605 White Transparent on Tomoe River paper. The ink had an average flow.
Overall, it's pretty well behaved. It's an interesting color, not quite my cup of tea, but give it a try, you might love it.
Disclaimer: A sample of this ink was donated for the purpose of this review. All photos and opinions are my own. There are no affiliate links on this page.