Collodion is a syrupy liquid that was the mainstay of the 19th century "wet plate" photographic process. Described in 1851 by Frederick Scott Archer, who gave his idea freely to the mprofession withut patenting it, (thinking that he was doomed to die in 6 months, but lasted 6 more years), the collodion, containing a dissolved halogen, was flowed on a piece of glass, then immersed in a silver nitrate solution to precipitate light sensitive silver halides in the coating. It need to be used immediately after coating, while the collodion was still tacky, hence the moniker wet plate.
I have not heard of any holograms having been exposed on this material, but it may be possible, as this material is extremely slow compared to conventional photographic film, but that might not necessarily mean that the silver halide crystals are of such a tiny size that they can resolve a holographic pattern. If someone sponsored my research I would be glad to try.
It is useful in a holographer's lab as an optic preserver and cleaner. If it is flowed onto a front surface mirror, or lens, it will protect it from scratches during storage; and when it is peeled off, any dust or grease on the optic and will stick to the collodion, leaving the surface clean!
Another use for it, as what its original application, is to form a bandage over cuts and scrapes. It is found on the shelves at drug stores, and this grade of pyroxyline is usable for cleaning optics.
Here is what the Photo-Lab Index from Morgan & Morgan has to say about it: