Unlike corrected grain leathers, natural or full-grain leather has the potential to age well and form a beautiful patina over time when properly maintained. However, not all full-grain leathers are created equal. Differing qualities of raw hides aside, the tannery's treatment and finishing of the leather can determine how easily the leather will take on a patinated look and how it should be appropriately cared for.
Leathers that have been tanned but not finished, i.e. remain uncoloured and without surface treatment, are referred to as being “in the crust”. The natural colour of crust leather normally ranges from off-white to yellow or light brown, and it is to be seen as a blank canvas for the shoemaker to work with, enabling the creation of fully custom colouration or “antiquing” by applying a combination of dyes and various pigmented creams and wax polishes.
While crust leather makes it possible to have rich, deep patination out of the box, it is also less forgiving to work with: when dyeing the shoe, it is not uncommon for previously invisible faults in the leather to suddenly reveal themselves, in worst case rendering the entire shoe a reject. The finished shoe also requires more frequent care to remain in splendor, as the dye and finishing sits mainly on the surface and is thus more easily affected by the inevitable occasional scuff or scratch. To summarize, crust leather is comparably high-maintenance but provides a blank canvas for antiquing, and easily develops an exquisite richness in colour and patina.
Aniline leathers, on the other hand, are pre-dyed and fully finished when they leave the tannery, where they are tumbled in drums containing aniline dyes, allowing the dyestuff to completely penetrate and saturate the leather. Most makers, even those otherwise known to prefer crust, use aniline leathers for black or dark shoes that are not supposed to show variations in nuance. Brighter coloured aniline leathers can of course also acquire patina with use, but at a slower pace than crust. Because of the more uniform and stable colouration, aniline leather needs less frequent appliance of pigmented cream and polish to look its best.