Either, it depends on which pen I pick up.
8th Grade English class, or rather “Language Arts.” 1974-75. Mrs. Townsend. She said to write assignments in either blue, black, or blue-black ink. I never heard of blue-black, but, yes, there was such a thing. But I haven’t seen it in decades, not that I really looked.
I liked those fat pens with 4 colors, blue, black, red, and green.
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One nun in Catholic school forbid ball point pens. We had to use cartridge pens, with messy little ink tubes.