What is the best way to preserve chlorophyll anthotypes?

I’m working on a 19th century photographic process called Anthotype. It basically involves using plant juices that fade when exposed to sunlight. For my light sensitive juice I’ve choosen concentrated alcoholic chlorophyll extract. After a little less than 20 minutes on full sunlight it fades completely! Where the normal exposure time for anthotypes is, say, 3 days.

But there’s a problem: Of course I know that anthotypes cannot be fixed and I’m trying to do research on it. There’s no reason why the untouched plant juices can’t be altered to be made iresponsive to light. This is the case of chloropyll, and you can combine it with copper sulphate to fix it completely.

The point is: I don’t have such chemical, and while I can get/ make it I have to store some prints I’ve made.

Is someone doing something similar? How can I prevent the photograph to overexposing after it has been done?

Some things I can try but don’t think will work are: Mordants, increasing the pH (chlorophyll is more susceptible to degrade under acidic pH), protecting the print with wax so to get rid of oxygen radicals that may destroy it, seling it on vacuum inside a plastic ziplock bag…

Any help is really useful!