Leather is widely used in all types of horse tack. While leather is sensitive to excessive dryness and moisture, it is also remarkably resilient. With proper care, it is often possible to restore leather to nearly new condition. Leather harnesses present a special challenge because the thin-strap goods are more prone to developing cracks than larger pieces such as saddles and boots. While some surface cracking is acceptable, cracks that penetrate the leather may allow the harness to break unexpectedly.
Clean the harness to remove surface dirt. Glycerine-based saddle soap is a good choice for cleaning all types of leather but any saddle soap that contains at least 50 per cent fat is fine for leather cleaning, according to Auburn University's Department of Animal Sciences. Dampen a sponge and squeeze out as much of the water as possible. Swirl the sponge in the soap to work up a stiff lather. Apply the soap to the harness in a circular motion, working on a small section at a time.
Remove all of the soap residue before continuing. Use a separate sponge to rinse the leather with as little water as possible. Working on the harness one section at a time makes it easier to remove the soap residue before it dries, which reduces the amount of water required.
Repeat the process until the harness is clean. It may require several passes with the sponge to get the harness clean but it is important that you remove all the dirt, mildew and mould before continuing.
Use a conditioner to moisturise the leather. There are many different choices in leather conditioners available. Neat's-foot oil is a traditional leather conditioner and is very effective. It does, however, have a tendency to darken leather. If you are restoring a light-coloured harness, choose one of the many leather conditioners labelled specifically for light leather. Apply the conditioner with a clean, soft cloth or even your fingers. It is important to get the conditioner in all of the folds and crevices of the harness.
Allow the conditioner to penetrate the harness naturally. Don't attempt to use heat or a fan to speed up the process. Allow the harness to sit in a clean, dry area while it absorbs the conditioner.
Repeat the conditioning process as needed. If, after the initial coat of leather conditioner absorbs, the leather is still stiff, another application of conditioner is required. It is better to make multiple thin applications of conditioner than to apply one thick layer.
Cover the harness with a soft, clean cloth. This will keep dust off the harness until you are ready to use it. Do not store the harness in a box or storage container. The newly moisturised leather may develop mildew or mould if placed in a dark, sealed environment.