I know this piece was done with Rust-o-leum Crystal Clear Enamel on top of torch. There is always going to be a loss of brightness but I do believe this enamel gave me fewer issues than other coatings. As far as patinas like greens, Japanese brown and such clear coats always appeared to darken the effect. I found it best to apply a light base coat, let it dry well and hit it again.
As far as the rosebud goes I really can't say. Never tried one, now I want to. I use a small torch tip, 0 or 1 depending on material thickness and desired effect. Larger area to me dictates a larger torch tip.