How do I change this to rust and verdigris using paint or chemicals?

There are tons of spray paints that will do the job and your end result will be what you expect. Chemicals can be iffy and dangerous.

There are chemicals to force verdigris for copper. It looks like tin, is It? You can take Verdi and rust with oil based paints. Mix the color you want and accent the areas you want.

Yay fir and then blue?

Rustoleum makes spray paint that looks like rust. Give it a coat and then use verdigris colors in acrylic to accent it? OR, get copper spray paint that has real copper in it, and it will darken and get the color after a period of time, or you can help it by spraying vinegar on it.

Modern Masters Metal Effects primer followed by ME metal reactive paints in both Copper and Bronze. The blue & green patina aging solutions oxidize equally well when paired together or individually with the Copper and Bronze Reactive Paint. I have a friend who has won 2 art competitions using these products on cardboard sculptures...the real-looking Verdi Gris finish is phenomenal!!

If the metal would naturally rust over time you could accelerate the creation of rust with chemicals. 25% water, 75% hydrogen peroxide, steel wool, and table salt. Submerge item until rust begins. My daughter, who is a scientist, calls my recipe instant rust and used it while teaching a chemistry lab.