Thank you all for your posts! :-)
I hope the images are not a problem, they resides on my website.
Anyway, the staining process was very simple: I applied only a coat of a water base stain then I wiped with a damp cloth (I did this because the final color was a little too dark).
Some people suggest to sand the first coat and to apply the stain again, this enphasize the flame. Another way to emphasize the flame is to apply first black stain, sand and then apply the final color. I, personally, prefer applying only one coat of stain without sanding: in this way the wood looks 3D, in few words, depending on the light angle, the pattern varies and the maple seams alive (the main problem is that to see this effect when you apply the sanding sealer).
I hope this will help, if not, don't hesitate to ask me again.
Thank you all again :-)