"Steaming" Walnut

I am going to buy some “sappy” walnut from my fav wood source. The one problem is… about 60% of the wood is the white sapwood and I like the distinctive black of walnut. They say that you can steam the wood to even the sapwood and heartwood.

Anyone have the skinny on just how this is done? Can you use a steam kettle, or do you need something bigger, like a steam room? Or am I stuck with trying to dye it to match?

Thanks for all your help!

God Bless,
Hawg

-- Saving barnwood from the scrapyards