I had this idea about a half caster that gets their Magic’s through a form of arcane ink they use to write runes. The runes they write decides the spell they cast. They can also dip weapons in the ink to give them improves them somehow. Every time you write a rune for a spell or dip your weapon in it, the amount of ink decreases. I need help with specifics.

mind helping me?

Palladium Fantasy has a class called The Diabolist. You can steal a lot of ideas from that if you can get a copy. It's all about runes and using different kinds of ink, even using silver, etc. You write these runes on plank boards, doors, as a tattoo, floors... You can prepare the spell in advance so you carry an arsenal and when you activate them it counts as a spell.

Check it out!

I know that Indestructoboy made a runekeeper class on the Dmsguild that revised and expanded upon the system that was introduced with the Rune warrior subclass. Might suggest you take a look over that, but I will say that it is long cause of how much the system was expanded.