Try and get to see the film 'Forgotten Silver' by Peter Jackson (the LOTR Man). This film used a lot of new material which the lab turned into all kinds of old movie footage.
When we had to make a 'old nitrate' film look we duped the shots onto B&W 16mm, then optically blown up to 35mm, skipping and adding frames to alter the speed. The exposure was also altered during the optical printing. Once this was processed Acid was dripped onto the film and left over night, the next morning we the reduped this again. It was all hit a miss but we finally got the effect.
It was very costly and messy. Which could be why Peter Jackson ended up buying the same Lab same years later?. These days he would do it on a computer!.