Robert Oster has two lines of ink: Signature and inkArt.ink. The former is readily available. The latter doesn’t appear to be available currently. I used the Signature ink for my comparison, but, for giggles, I included a chromatography strip of the inkArt.ink (IAI).
For those familiar with Organics Studio, you’ll know that at any given time, a certain ink may or may not be readily available. For that reason, I’m dubbing it “usually available.”
If you have any suggestions for future comparisons, let me know in the comments. And check out my other Ink Dupes posts.