1969 Samoan Tala & Toning Troubles

Myself, I prefer coins that are toned most of the time. Generally, toning shouldn't be doing any damage to the surface of the coin, but old plastic holders like that one can contain PVC which will eventually cause damage. You could take it out of the plastic holder and put it into something more inert. An Airtite, or a 2x2, perhaps? I also recommend gently bathing the coin in a pure acetone bath, then letting it dry before you encapsule it away again. Don't rub! (You probably already know all of that already, but better safe to explain in too much detail now, instead of after the fact.)