Poly is obtainable at high purities and yields using industrial processes by causing a secondary amine and formaldehyde to react with a polyphenol, and then breaking down the aminomethyl group of the obtained polyphenol by means of hydrogenolysis in the presence of a hydrogenation catalyst. Independently energizable wire coils are linearly aligned with one another in a vertical direction on a buoyant body. According to the invention, a clear coating layer over color layer can reproduce an even more accurate gloss than in the prior art and presents the desired surface properties in the absence of steps even if there is unevenness in image recording density, whereby the image has a sufficiently improved texture to look more real. Forming a part of the soil drying machine is a tilling implement.