[Frameworks] black mask on colour print film

[Bernd Luetzeler]

Dear Frameworkers,

I need to find out how to cover one half of a 35mm colour print film with a black mask (after processing).
Of course the first thing to try is an optical printer (before processing) and I will explore this option in the next few weeks.
But as an alternative I already started thinking about other options:
Since it is always either the left or the right half, I think it could be possible to apply a vertical strip of black over the whole print.
Is there any paint, ink, marker or tape or other material, that fully blackens film and that does not come off during projection?

Would be great to hear your experiences

Bernd