What makes an ink "safety pen ink"?
My research suggests any ink containing gum Arabic probably qualifies. Beyond that I'm mystified.
I believe I read here on FPN that Noodler's Whaleman's Sepia (a fave of mine and I should probably buy at least one more bottle before it's gone forever) was developed for the Noodler's Boston safety pen. Whether this is true or not, it is the only ink I've ever had in my Boston safety pen, quite coincidentally.
I was searching for something else when I found a shop offering four Noodler's inks - three sample-only sizes, one 4.5oz bottle - described specifically as "for use ONLY with Noodler's Boston safety pen or dip pens." (Emphasis not mine.) I cannot find any info about these inks on the Noodler's website or anywhere else that might explain the safety pen restriction.
I don't need a dissertation, but an executive summary would be most welcome!