When I was in high school, I used to pick some flowers, especially roses, along the road where I traverse everyday. They were tiny roses which were commonly called as native roses. ( I don't know if that is the exact name. Whatever!) There was a time, I tied a rose taken from a neighbor's garden on the window near my bed so that I could smell its fragrance while I lied down. I left it there hanging. I was waiting for it to wilt, but never it did wither even after a week. Here is what I have discovered.
Air drying method could preserve a rose.
This method is best for rose buds that are just about to open. Hang them in a warm, dry and dark place with good ventilation for two weeks. I think it is best to tie a string around the stems and hang them upside down. This will prevent moisture from becoming trapped between the flowers which can mold them. Once they are completely dried be sure to handle them with care for they will now be brittle.You can display them tightly in a terracotta pot. They will make a wonderful display.
Disclaimer: the photo is not mine