I am not sure if anyone is still following this forum but anyway...
I have used a variety of leaves and found that the ones that work best are the type that grow in shaded areas such as nasturtium, ayrum lily and spinach.
I have used the leaves whole and contact printed onto them using a positive inkjet transperancy (two layers of the same image), I use the sun to make my exposure which could be from 2 hours to 1 week depending on the weather. I was doing this is New Zealand but it was Wellington and during winter, I haven't tried it since moving to the Northern hemipshere.
I also extracted the chlorophyll from silverbeet without using any chemicals and painted that onto paper and made a print in the same way as before. It works quite well but the range of tones is less than a leaf itself.
I exhibited my leaf prints inside behind UV glass and they did fade much to my horror. The ones that have been stored in an album have not faded at all.
I have tried asking a few scientists about how to "fix" them but no luck so far.
Very nice images you produced there.
I am interested in trying this process. The suggestion of blueberries seems interesting, or maybe red wine. We'll see what comes out!