Strolling along the railway, one can often see a row of wooden sleepers that are so black they shine. Someone takes a photo and posts it online, commenting on how thick the paint is. Immediately, someone responds, saying that the entire piece of wood was soaked in oil. The two sides argue heatedly, and it's hard to tell who is right for a moment. But if we go through the process of making sleepers from start to finish, we will have a better understanding. The color comes earlier than expected, and the middle painting process is almost done. The first few processes make room for it, while the later ones help the color settle in.

First, let's talk about the origin of this piece of wood. Pine is often used for making sleepers due to its smooth grain and rich oil content, which are suitable for the subsequent process. The raw wood is brought into the factory, peeled, and sawn into square pieces according to size. In the industry, these are called plain sleepers. At this point, they are light-colored, no different from the wood used for making cabinets at home, and no one could have predicted that they would eventually turn black like that.

The square blocks from the new saw contain a lot of water, which needs to be stacked up and slowly dried. When stacking, the bottom should be elevated to allow air to pass through. It's not advisable to quickly dry them in the sun. This task cannot be rushed; it's similar to drying persimmons in autumn. No matter how quickly the outside dries, the moisture inside will move out at its own pace. Only when the wood is cool both inside and out can we consider this stage complete.

After drying thoroughly, there is another seemingly strange task: carving shallow notches on the surface. The purpose of carving these notches is to create a path for the next item to pass through. Pine wood has dense fibers, and if we rely solely on the surface to slowly seep, the penetration will be neither deep nor even. Once the shallow notches are carved, there will be a pathway inside that can be followed. It should be clarified here that the carving is done all over the entire piece of wood, from end to end, and no single side is left unattended.

Next came the step of determining the color. Su Zhen pushed the large jar forward, closed the lid tightly, first evacuated the air inside, then poured in the warm oil, and gradually increased the pressure. The oil flowed along the shallow mouth carved earlier, layer by layer into the fibers. When all the necessary ingredients had been added, the pressure was released, and the excess was retracted. By the time the jar was opened, the entire piece of wood had turned pitch-black, evenly from the outside to the inside.

Here, we can answer the question asked online. The color applied on the surface is visible, but when you saw it open, the inside is still the original light color of the wood. After the process in the tank, the black color penetrates along the fibers, making everything black wherever you saw it. It's like pickling radishes at home for a whole winter, where the sauce color slowly seeps from the skin into the core. When you cut it open, it looks the same inside and out, and you can't remove it by wiping.

The process doesn't end with the discharging from the kiln. The freshly discharged sleepers need to be left on the site for a while to allow the wood to relax and the color to even out. Just like freshly baked Mantou, they also need to stay in the drawer for a while longer, and it's useless to rush them. After this period, they are bundled and loaded onto the truck, and only then is a sleeper truly ready.

This black color is versatile. It can be seen on old railway lines, and it is also used on the small tracks used to haul ore in mining areas. Some factories even lay out a dedicated track from their entrance to the freight yard, and they still use this kind of wooden sleeper underneath. The workplaces vary, but the job of the sleeper remains the same. It supports the rails and aligns them neatly, one after another. Pine wood is inherently soft, so when the wheels of the train pass over it, it gives a bit before firmly resisting. This rhythm is repeated no matter how many trips are made in a day.

Interestingly, despite the name changes of the running cars and the repeated repairs of the tracks, the appearance of this piece of wood has remained almost unchanged over the years. From a distance, it still appears as a row of black and shiny wood, not particularly eye-catching. Passengers staring out the window would never bother to count it. However, without the series of processes that have been carried out, this row of black wood would not have been achieved.

Passing by the railway again and seeing that row of black wooden sleepers, you can probably guess how many hands it has passed through. A piece of pine wood, after being dried and carved, stayed in a tank, and then quietly lay under the rails after being stored for a while. The black color was set at that time, and from then on, it was exposed to the sun and rain year after year, and the joints began to form.