There’s probably a good chemical reason why vinegar and salt don’t like each other, but I don’t know what it is. I was probably too busy making ink pellets in the back row when that relationship was explained in Chemistry class.
The enmity is very useful, though. For when you’ve been out in the rain a lot (as happens frequently at this time of year) or been sweating rather profusely (as happens in the other half of the year), vinegar is the best way to tackle the salt stains that can result.
As the leather of your shoes absorbs water, salt gathers at the high-water mark – usually about half way up the vamp and an inch high around either side. If this is allowed to dry and not tackled quickly, it can leave a permanent ridge on the leather. Like scum left by a retreating tide.
You have to wait for your shoes to dry though. So wipe off any excess water when you get back home, stuff the shoes with newspaper, and keep them away from any artificial sources of heat. Then put your shoe trees in to stop them losing their shape.
When the shoes are completely dry, make up a mixture of 50:50 water and vinegar. You’ll need a couple of inches in a mug, and some cloth to apply it with. Most vinegars will do – malt vinegar is ideal but I used rice vinegar most recently and it worked fine.
Dip the cloth in the mixture and rub it over the salt stains. The leather will noticeably darken as it absorbs this new liquid, but don’t worry about that. Concentrate instead on the ridge of salt that stands away from the shoe like dirt. You want to keep rubbing the solution onto this ridge, and reapplying, until it dissolves and the leather is smooth.
When you’ve done this successfully on both pairs of shoes, wipe off any excess solution with a clean part of the cloth and leave them to dry. After a while the leather will dry and return to its normal colour. Now give the entire shoe a generous polish. A cream similar in tone to the leather will work particularly well, as it is likely to correct any colour differentiation caused by this process.
The shoes should be as good as new. The treatment can be used on old stains as well, but the salt is far harder to dissolve. You can apply polish or cream to remove the white colouring, but a ridge will remain.