The first step in making a collodion negative begins with a solution called, not surprisingly, collodion.
Photographic collodion is a mixture of raw cotton (which has been treated with nitric and sulfuric acids) dissolved in ether and alcohol, with a little iodide and bromide mixed in. What exactly it's made out of doesn't really matter that much, though -- in 1880 you can buy it pre-mixed. What matters is that this solution is transparent and sticks to nearly everything.
Pour the collodion onto a glass plate, then the tilt the plate until its entire surface is coated with the solution.
Then pour the excess collodion back into its bottle.