In order to properly preserve the wood, four steps must be thoroughly completed.
STEP ONE: Consists of burning the wood which is most easily done by using the traditional approach of a controlled fire (a propane torch can be used as a more modern approach). The goal is to aim for apply scorch marks to the wood while still leaving the top layer of wood intact (not completely scorched).
STEP TWO: Scorched wood must be disrupted with a wetted wire brush which will result in a lighter surfaced wood.
STEP THREE: Brushed wood is then washed off with water and then dried completely to remove any excess materials that could impact the success of preservation.
STEP FOUR: The scorched, brushed, washed and dried wood then covered with an oil finish to preserve a natural look of the wood and ensure an extended preservation duration.
All information was retrieved from http://shousugiban.com/overview/
The attached video displays some of the initial scorching prior to brushing, cleaning and oiling.