While all logs carry the underlying color of the type of tree from which they were hewn, not every homeowner is satisfied with the look of the wood. Stains are the most common way to change the color of the wood to something different, but there are more options than just commercial, chemical-based stains. Natural oils can change the color of wood, as well as preserve it, and are environmentally friendly in comparison to chemicals.
Oil is no different than chemical stains in that the wood needs to be cleaned and ready for the application of the coloring. Dust and debris block the absorption of oil. If working with new logs, clear away any loose fragments of bark left behind, and completely sweep the surface clean with a stiff broom. If working on older logs, consider using a power washer to blast the surface clean of dirt and grime, and give it 72 hours to dry before applying any oils.
There are many different types of natural oil to use, ranging from linseed and walnut to tung oil and olive oil. Each has its own unique way of soaking into the wood, and each has its own depth of color. Just as with a chemical stain, never apply the oil to the logs until you have tested the stain you desire in an out-of-the-way area, or on a piece of scrap wood. Bear in mind that multiple layers of oil result in deeper shades of stain, so always start lighter and apply more coats if you desire a darker finish, because you cannot work your way back from darker to lighter.
Oils are best applied to wood directly with a paintbrush as opposed to a sprayer, which clog with thicker oils. This also allows you to ensure the oil is pushed into the nooks and crannies spraying might otherwise miss, which is important since oil acts not only as a coloring agent, but also as a natural sealer and water repellant. Apply liberal amounts and go for total coverage, allowing the oil a chance to soak into the wood for maximum results. Never apply more than one coat at a time to avoid accidentally over-staining, and bear in mind some oils, such as linseed, take a week or more to dry -- so pay attention to the weather before working on outdoor log projects.
Since oils do not have any chemicals in them to boost their durability, they need to be reapplied on a regular basis. Every six months to a year is a good idea, in comparison to some wood stains and sealers, which only need to be reapplied every few years. In areas where there is direct sunlight or constant weathering, you may find you need to reapply the stain more frequently, as sunlight fades colors, and constant water and weather cause additional fading.