Answer
The mulberry harvested in Mikura Island or Miyake Island, Tokyo Japan, is called "Island mulberry" (Shimakuwa). It is sometimes called "Golden mulberry" because island mulberry looks golden yellow depending on the angle of sunlight. (Very rarely, a few Honkuwa look golden yellow.)
In addition, some island mulberry has MOKU (knot-like wood grain). Rare and beautifully-shaped MOKU is highly valued and very popular among serious collectors of Gosu. It costs 500,000JPY or more.
Mikura Island and Miyake Island, where island mulberry is grown, are active volcanic islands. Therefore, these islands have totally different soil from other areas, very steep mountains, strong wind, and mild climate. All these factors make island mulberry high quality wood.
The reasons for higher price of island mulberry are the rarity, the facts that they are harvested in limited area, only two small islands. Island mulberry is used to make not only Go box or Shogi piece box and piece stand, but also very expensive tea utensils.
Regarding regular quality island mulberry, the price is not so high, but if island mulberry has MOKU (knot), the price is determined based on the condition of MOKU. Honkuwa (Mountain mulberry) is usually less valued than island mulberry.
