I get lots of questions about inks. There are a lot of good ones out there and a growing number of bad ones.
Be sure any ink you use is made for fountain pens, not dip pens or drawing pens. Never use India ink.
A good rule of thumb is to use an ink made or sold by a fountain pen manufacturer. They are generally not going to make an ink that messes up pens and causes them to have to do warranty work. The sole exception would be Diamine inks, not made by a pen maker, but very safe and offered in a wide variety of colors and tints.
My preferred ink list includes, in no great order of preference, Parker Quink, Pelikan 4001 or Edelstein, Waterman’s, Aurora, Pilot, Diamine.
Please note: the use of pigmented, shimmer, or glitter inks will void The PENguin warranty. I cannot be responsible for pens in which those inks have been used.
I also get asked about Noodler's. Basically, the answer is that those inks are much too saturated. They are not solutions, as inks should be, they are suspensions, and the precipitates can clog pens. In addition, many of the dyes used by the maker are too saturated and stain pens.
Finally, some disclosures. I am not a chemist and don't play one. I have never used Noodler’s but have gathered my data directly from users and pen manufacturers.
Most importantly, I have repaired pens that have used these inks and have seen the staining and the actual corrosion of parts.
So, for all those reasons, I strongly recommend against the use of these inks and will not warranty pens in which they are used.