Counterbalanced Ventian Blinds

Some of the windows in our house used to have mini-blinds, the cheap, thin, lightweight aluminum blinds that were all the rage ten years ago. Or maybe 30 years, or maybe they are still all the rage. Whatever. We used to have some, but they got old and battered and we ended up replacing them with real venetian blinds. Made of cast iron. In Venice. By dwarves working deep underground. Whatever. They are substantial and heavy. They work well enough, they are easy to tilt to admit light or block the view, but it takes some real oomph to hoist them open, for instance, if you need to open the window. So I just realized that what these things need is a spring to counterbalance their weight, kind of like an overhead garage door. A counterweight would be simpler and more reliable, but would require more mass, and a more complicated installation. A spring would require some stout mounting screws, but that is about it.