I have found that Borax acid works best when you use a disposable container (coffee can), with boiling hot water in it. Add Borax crystals until you have a supersaturated solution (when no more borax will dissolve). Put it on the wood with 00 steel wool and scrub use lots of the solution. Leave it on for a few minutes and then wash/rinse it off with clear water.

Notes:

This will lighten the wood and raise the grain.

Use good gloves such as rubber gloves for washing dishes, this stuff is tough on the hands.

Don't let the borax solution to dry on the wood.

Do it outside with the garden hose nearby to rinse off your work.

Have a couple of rags ready to dry the wood when done.

Jason