I'm looking for an instrument that creates the sensation of a knife on skin, without cutting (and optimally without actually scratching).

Background:

I recently started seeing someone on a f basis. We're both interested in trying new dynamics and sensations, but fairly inexperienced. I would describe myself as a gentle dom, while my partner takes a submissive role most of the time. I am really concerned about consent, and communication has helped a lot so far!

This person used to cut themselves when they were younger, and is now turned on by the sensation of knives on their skin. I stroked and scratched them with a knife in the past sessions, but the last time the knife was sharper than I expected, and I left quite the amount of bleeding wounds on them.

I am not a fan of this, and my partner is indifferent to blood. I like the idea of leaving marks, but I'd rather paint on them than cut. This would have the benefit that the marks could be removed quickly, as being seen with them could create problems in my partner's daily life.

It seems as if it's not the "weapon" aspect of knives that's a turn-on, but mostly the feeling of sharp metal on their skin.

Any advice is appreciated. Cheers!