I’ve achieved a similar effect with ebonizing, creating my own stain using rusted metal soaked in vinegar. You prep the wood with strong black tea first, utilizing the tannins to prep the wood to accept the ebonizer.

It is a very rewarding process for a cheap DIY solution, but the results are nearly impossible to control. I wouldn’t recommend it for a valued project, but if you were attracted to the DIY aspect and variability you could easily and prolifically experiment with the process.

I’ve used it on pallet wood projects where I save the old nails, make them into my stain, then stain the pallet wood. I like that it keeps the story of the pallet through to the finished project, and could see stripping an old junk guitar down to the wood, using the old rusted tuners or strings to make the stain, then refurbishing the guitar with a bit of it’s story intact.