Hello, darling!

My hair was bleached blond for 3 years. Now I wanted to switch to my old time favourite color: copper. My natural hair is medium-brown so just applying henna and cassia would only leave me with orange lenghts and dark red roots. So I decided to go with the normal copper dye which lightens my roots quite well. The problem is that my lenghts being blonde, the color washes out very fast.
I read somewere that you can make a henna gloss, that is not as permanent as just applying henna on hair.
I was thinking of mixing a bit of henna with cassia and a lot of conditioner and apply it in between my hair dyeing sessions, just to preserve the color more and also condition it.
My questions for you are:

1. Have you ever applied a henna gloss ontop of chemical dyed hair?
2. Being just a gloss, could it interact with future dyeing processes? Even if the henna is 100% natural.
3. Does it really have some color payoff?

Thank you