Creosote is a wood preservative that is generally used in industrial applications such as railroad cross ties, telephone poles and piling. It is not used for commercial purposes in which the final product is to be used for and around people. From a distance it has a sweet smell, but as you get close to the treated item the smell is overpowering and can be harmful. If an item treated with creosote comes in contact with skin it can cause a problem such as a rash. This is one of the oldest commercially used preservatives. It is a brownish/black oil that is distilled from coal tar. It has been highly successful in prolonging the life of wood in contact with the soil or in wet conditions which are conducive to the promotion and longevity of fungi. The preservative is forced into the wood using a special pressure treating vat.
Once the creosote is in the wood it will not leach out of the wood with water. It also has a high toxicity and thus fungi are deterred from attacking the wood for decades. It penetrates the wood easily under a pressure treating system and is cost effective.
Creosote is not available to home owners for use around house or farm. In fact it should never be used where farm animals or humans come in contact with it. In the South a problem surfaced many decades ago where pileated woodpeckers were attracted to the smell of creosote and pecked nesting holes into telephone and light poles. They would proceed to lay their eggs which never hatched due to the toxicity of the creosote. The eventual solution was to mail a wire mesh around the pole at the height that these woodpeckers normally built their nest holes. If this was not done the population of these large woodpeckers could have been seriously decreased.
Another note of interest in terms of creosote treated timbers is their recycling after they have completed their useful service such as old railroad ties. Some people have purchased old railroad ties to use in construction such as in a log home of sorts. The inside of the home is finished in a conventional manner and the outside may be finished with rough sawn lumber. Thus the core of the home is built of old railroad ties. Bad idea! I knew of one couple who lived in such a home and then they noticed that their cats were dying of cancer. The doctors advice was to move out of the home and have it demolished.
I have seen people scrambling along the railroad tracks picking up old ties that were broken into manageable chunks during their removal from the rail bed. The 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 that one will have to content with. Even with old creosote timbers used for posts, a good painting will last for a short period of time as the wood preservative bleeds out through the paint.
If one would be able to obtain a bucket of creosote and paint it one the wood before using it as a fence post or other ground contact purpose, it is a waste of time as it will do little to deter rot in anything but the short term. This also goes for straight tar. If you want to prevent rot in any high rot susceptible uses it is advised to obtain pressure treated materials from a lumber yard. What they sell to the public will be considered safe for its end use and will save time and money in the long run. If you try to be a home grown wood technologist you are doomed to fail in your endeavor.