Creosote is a wood preservative typically used in industrial applications such as railroad ties, telephone poles, and pilings. It is not used for commercial purposes where the final product is to be used on and around people. From a distance it smells sweet, but as you get closer to the treated object, the smell is overwhelming and can be harmful. If an article treated with creosote comes into contact with the skin, it can cause a problem, such as a rash. This is one of the oldest commercial condoms. It is a brown/black colored oil that is distilled from coal tar. It has been very successful in prolonging the life of wood in contact with the ground or in humid conditions that favor the promotion and longevity of fungi. The preservative is forced into the wood using a special pressure treatment tub.
Once the creosote is in the wood, it will not leach out with water. It also has high toxicity and thus fungi are deterred from attacking the wood for decades. It easily penetrates wood under pressure treatment and is cost effective.
Creosote is not available to homeowners for use around the house or on the farm. In fact, it should never be used where farm animals or humans come into contact with it. In the South, a problem arose many decades ago when woodpeckers were attracted by the smell of creosote and pecked at nesting holes in utility and telephone poles. They would proceed to lay their eggs which never hatched due to the toxicity of the creosote. The final solution was to place a wire mesh around the post at the height at which these woodpeckers would normally build their nests. If this had not been done, the population of these great woodpeckers could have seriously declined.
Another note of interest regarding creosote-treated wood is its recycling after having fulfilled its useful service as old railroad ties. Some people have bought old railroad ties to use in construction, as in a kind of log house. The interior of the house is finished in a conventional manner and the exterior can be finished with rough sawn lumber. Thus, the core of the house is built with old railway ties. Bad idea! I knew a couple who lived in a house like this and then they noticed that their cats were dying of cancer. The doctors’ advice was to move out of the house and have it demolished.
I have seen people clambering along railroad tracks picking up old ties that broke into manageable pieces during their removal from the rail base. People were gathering these pieces to use as firewood. The end result of this practice can only be health problems. Creosote cannot be painted, so the black surface is something one will have to be content with. Even with old creosote lumber used for posts, a good paint will last a short period of time as the wood preservative leaches through the paint.
If one could obtain a bucket of creosote and paint it on the wood before using it for a fence post or other ground contact purpose, it is a waste of time, as it will do little to prevent it from rotting on anything not be short term. . This also applies to pure tar. If you want to prevent rot in any rot-susceptible use, it is recommended to get pressure-treated materials from a sawmill. What they sell to the public will be considered safe for their end use and will save time and money in the long run. If you try to be a homegrown wood technologist, you are doomed to failure.