The raw material “natural rubber” arrives at the factory from raw rubber processing plant. Natural rubber is produced by solidifying the sap collected from rubber trees, and it is delivered from designated factories in Southeast Asia. Only natural rubber of particularly high quality, with few impurities, is carefully selected. Incidentally, these blocks of natural rubber are standardized at about 33.3 kg under international regulations.

Natural rubber and additives are blended. Pressed and mixed to soften. The next step is blending natural rubber with additives. This is done with a machine called a Banbury, which has two mixer-like blades inside. The Banbury crushes the natural rubber while blending it with additives. Because the properties of natural rubber differ slightly depending on its origin, the additives are blended in ratios tailored to each.

The number of kneading times is crucial for thorough mixing. Delicate judgment is the work of a master! After blending natural rubber and additives in the Banbury, the mixture is kneaded further with large rollers. This process is handled by veteran staff with many years of experience. By checking the firmness while mixing, they determine how many more kneads are needed for complete blending. This delicate judgment is truly the skill of a craftsman.

More than half a day is spent carefully maturing, allowing the additives to settle in. The rubber, evenly mixed by the craftsman, is thoroughly rid of fine foreign matter such as wood chips, then solidified into blocks of about 20 kg each. From there, it undergoes more than 12 hours of maturation time. By letting it rest patiently, the additives settle in firmly. The process of strong mixing and resting is somewhat similar to bread making.

Advanced kneading determines “stretch” and “colour.” A new craftsman takes over. Once maturation is complete, the rubber goes to the next craftsman. It is fed into temperature-controlled rollers and kneaded together with sulphur, which gives elasticity, and pigments. To eliminate variations caused by ambient temperature, humidity, and the natural rubber’s characteristics, kneading time is adjusted based on experience and intuition. This is another critical process where craftsmanship shines.

Extrude and heat it… and suddenly, elasticity is born! Before the kneaded rubber cools and hardens, it quickly moves to the next process. After being extruded into hose-like shapes and heated, it transforms into beautifully coloured rubber with excellent stretch. The reason is that heating causes sulphur to give the rubber elasticity. Now, the product is almost complete!

Slice it up, and the forming process is complete! Just waiting for finishing. The hose-shaped rubber is fed into a machine and cut one after another. The rubber now appears in the familiar ring shape! The size and thickness of the rings are determined by the mold used in the “extrusion” process, while the width of the cuts in this “cutting” process creates various types.

Wash thoroughly, dry completely, and make clean rings. Until cutting is finished, powder is sprinkled on the rubber to prevent the insides of the rings or the rubber surfaces from sticking together. This powder is first washed away with hot water, then with a special cleaning solution, and finally dried thoroughly in a giant machine. Because of the considerable weight, lifting and loading it is tough work—done by two men together.

The finishing touch is by hand. Each one is sent out with care. Finally, in a dedicated room, the bagging process begins. Is there any foreign matter? Are different types mixed in? Are there defective products? After strict final checks, the quantity is adjusted, and each is carefully packed by hand. With the wish that “we want people to use them with peace of mind and in abundance,” the rings are sent out to everyone.