rubber

Japanese: rubber

…Therefore, in the broad sense, mortar refers to any tool used to crush, grind, or mix things, and it is extremely diverse. In the Stone Age, pounders (crushers) used for pounding and rubber (grinders) used for grinding already showed a certain degree of differentiation, but some tools could be used for either depending on how they were used, making it difficult to distinguish between them. As these tools gradually became larger and more efficient, various forms of mortar tools were developed and their functions became specialized. …

From [Rubber]

…All three have a similar chemical composition, with 40-60% triterpene resin, 10-15% isoprene polymer rubber, and the remainder ash and polysaccharides. (3) Elastic rubber is the main raw material for rubber products that we see every day. However, when we say rubber, this is what we generally mean. …

*Some terminology explanations that mention "rubber" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…そのため，広義には臼はものを砕いたり，磨りつぶしたり，まぜたりする道具一般を指し，きわめて多岐にわたっている。石器時代において，搗き砕く目的につかう叩き石pounder(crusher)と，磨りつぶす目的につかう磨り石rubber(grinder)とは，すでにある程度の分化を示しているが，使い方により，どちらにも共用できるものもあり，その区別はつきにくい。これらの道具がしだいに大型化あるいは効率化してゆく過程で，さまざまの形態の臼に属する道具が発達し，その機能も専用化されてきた。…