Robert Oster Darkstar Blue is exclusive to The Darkstar Collection. I really wanted to try this ink but couldn't get my hands on a sample so I put a request out on the Pen Addict Slack channel. Thank you to @tinybadge on Instagram for sending a sample over.

The color:

Darkstar Blue is a beautiful dark blue with a purple undertone.

When pooled there is a tiny bit of dark pink sheen around the edge, but not much. The sheen is not visible in writing.

Let's take a look at how the ink behaves on fountain pen friendly papers: Rhodia, Tomoe River, and Leuchtturm.

Dry time: 20 seconds

Water resistance: Low

Feathering: None

Show through: Medium

Bleeding: None.

Other properties: Medium shading, a tiny bit sheen, and no shimmer. The sheen is only visible in large swabs on Tomoe River paper.

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): Robert Oster Evening Sapphire, Robert Oster Darkstar Blue, and Robert Oster Midnight Sapphire. Click here to see the Robert Oster inks together. Evening Sapphire is lighter than Darkstar Blue, but Midnight Sapphire seems very close to Darkstar Blue.