Different types of Bleaching Process
Bleaching is a chemical process that lightens the color of wood. Wood can be darkened by several processes, ranging from the natural to the accidental. What process caused the wood to darken would determine which of the three bleaching processes you would use to lighten it.
Chlorine bleach is the best choice for removing dye stains, and some organic stains such as grape juice and tea stains.
Oxalic acid is the best choice for removing black iron or water stains.
TWO PART WOOD BLEACH
For certain effects you need to use the two part bleaches. Part A is Sodium Hydroxide which opens up the woods pores and then reacts with the Hydrogen Peroxide in Part B.