It is impossible to predict what will happen with every combination when you mix fountain pen ink to create custom colors. Once Alan mixed Noodler’s Year of the Golden Pig and Noodler’s Georgia Peach to try and get a golden-yellow highlighting ink and it created a gel! This result certainly would have messed up the ink flow in any pen! To save you from some unexpected results, there are a few fountain pen ink mixing combinations that you may want to avoid.
When mixing blue-black fountain pen inks it is good to be cautious since some blue-black inks, especially older formulas, contain iron which makes the ink acidic and corrosive to fountain pens. Mixing some blue-black inks can also cause clogging.
Mixing inks can change or neutralize any special properties that they may have. For example, Noodler’s “bulletproof” inks (waterfast, fade resistant) when mixed with conventional inks loose their special “bulletproof” properties. Noodler’s Polar Blue or Polar Black inks may lose some of their freeze-resistance when mixed with regular inks, however, we do not live in a cold enough location to test this out. Does anyone have experience with this?
The formula of Noodler’s Baystate Inks is styled after vintage inks and has a different pH than all other Noodler’s Inks. This ink was not made to be mixed with any other ink except for other Baystate colors! In addition, the Baystate inks each have slightly different properties. Baystate Blue is waterproof, but Baystate Concord Grape is only partially water-resistant and Baystate Cape Cod Cranberry is not waterproof at all. These inks are a favorite of some writers because they have a very high color intensity and look dramatic on certain paper grades, so it is nice to know what their limitations are.
Do you have any fountain pen ink mixing nightmares or warnings that you wish to share with us?
by 
I had Noodler’s Antietam in a Waterman Charleston. Last night I emptied and refilled with Eel Blue the convertor only. No cleaning. I am getting a pretty nice green color. Nr
I love Noodler’s Polar inks and since just getting the Winter 2008 Edition Polar Brown I now have them all. I’ve recently mixed my Polar Blue with my Polar Black, in a 7:1 ratio, and it’s a gorgeous blue/black [similar to Noodler’s Aircorp Blue-Black and nowhere near to a dark NAVY blue color]. It also retains all of the qualities of the Polar inks such as the Eel lubricants, totally “bulletproof” even when swabbed with pure bleach, plus retains the Polar “freeze-resistant” aspect [I placed a Noodler’s modified Preppy eye-dropper pen filled with this Polar blend in my freezer set at 0°F overnight and the ink never froze, never even thickened slightly and wrote perfectly while still below freezing!]. I haven’t yet tried Polar inks mixed with my other non-Polar Noodler’s inks in my freezer, to see if they maintain freeze-resistance [as you’ve asked “Does anyone have experience with this?”, but I will do so and post back ASAP. The other Polar/non-Polar blends I’ve used were; Noodler’s Polar inks mixed with non-Polar such as Heart of Darkness, Borealis, and Nikita… even tried a blend of Polar & “bulletproof” Blue Ghost-Invisible Ink that only lightened the Polar inks and lost the UV reactive qualities of Blue Ghost entirely… I can, however, honestly attest that my Polar Blue-Black blend, a 7:1 ration of P-Blue to P-Black is an awesome blue/black ink color. My Polar Blue-Black has some really nice shading too when used on quality paper/s, retains all of the Polar freeze-resistance and Eel lubricating properties, plus it cannot be washed out with anything once fully dried! I use this Polar Blue-Black blend in my daily-writer now in my Journals, for signatures [fraud-proof] and anywhere I need to use a permanent or “bulletproof” ink. I’ve been thinking of placing a Noodler’s eye-dropper pen filled with my Polar: Blue-Black blend in a glass of water, place in my freezer until all the water froze solid around the pen, then take some pictures/ videos of me writing with the pen still encased in solid ice, just to show and prove that it does indeed still write beautifully when below freezing in a solid cylinder of ice! I’ll probably post this as “Pen frozen in ice, still writes!” on the FPN forums for all to see, once I get this done. I absolutely love all my Noodler’s inks [I’m not affiliated in any way with the Noodler’s Company, the owner, or their affiliates, I just love their inks]. The Polar inks are my all-time favorites now, despite living in a tropical area where it gets into the triple-digits in the summer and sometimes gets well below freezing a couple of months/days out of the year in the winter. I just really like all the Noodler’s inks [not just the Polar inks but they are my favorite inks made by Noodler’s]!
I have a large bottle of Noodler’s Nikita Red and several different blue inks, and I wanted to experiment with mixing them to try to get a nice purple ink. I tried Iroshizuku Kon-Peki, Diamine Mediterranean Blue, and Private Reserve DC Supershow Blue.
Utter disaster. All combinations came up a kind of rusty, muddy brown. Whatever it takes to create a purple ink, it isn’t Nikita Red and any of the blue inks I tried.
I did put a drop of Iroshizuku Mirasaki-Shikibu (purple) on a facial tissue (Kleenex), and then put a few drops of water on it. It’s a genuine purple ink; when the color spread through the tissue, it stayed uniform purple everywhere.
By contrast, I did the same thing with a drop of Pelikan 4001 Violet, my favorite purple ink, and the water drop test was interesting. The water pushed much of the red color out of the ink first, driving it away from the drop very quickly. The remaining bluish-violet color spread out much more slowly.
There’s a fair amount of red in Pelikan 4001 Violet, which is why I like it so much. It’s a bright, vibrant purple, not (despite its name) an actual violet, which would be much closer to blue.
Anyhow, mixing red and blue inks does NOT make purple…at least not with any of the inks I used. I suspect that it probably would take something like a cyan+magenta combination to actually get a purple. I don’t think red and blue can work.