How to Keep Rain from Ruining your Leather Tack
While the leather is still damp and its pores are still open, apply a light coat of a penetrating neutral pH leather conditioner which duplicates the fat liquors tumbled with freshly tanned hides to make them supple. Capillary action will pull the conditioner down between the fibers. Thick or waxy conditioners tend to stay on or near the leather's surface, so look for conditioners with a neutral pH and avoid cleaners or conditioners with a harsh, alkaline pH. An alkaline pH, such as that of soaps, can damage and eventually weaken leather fibers.
An Ounce of Prevention
One thing taking quick action to re-lubricate your leather can't do is to restore its appearance once dyes are affected. The water will have moved some dyes, leaving spots, splotches, and streaks when it finally evaporates. “Erasing” these water marks is almost impossible once they occur. Often, stripping and re-dying is the only recourse to restore an even colour or the original depth of colour.
Preventing the problem with an appropriate waterproofing product is much easier. Determining which water protection product is most appropriate depends on both your purpose and your personal preferences about things like application methods, odors, and how the product affects the leather's surface.
Silicone polymer sprays are non-greasy and can be used on suede as well as smooth leather. However, they can make leather surfaces slippery, affect the colour of porous leathers, and have a drying effect on leather if overused.
Acrylic copolymer is the newest option for waterproofing. It forms a microscopic net too fine for water molecules to penetrate but porous enough to allow water vapour to pass through. It creates a unique, flexible coating that protects leather fibers from rain, maintains the breathability of leather, is not slippery, and actually acts to fix dyes in porous suede.