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I am copying an email I received regarding two-tone stain on plywood:

" I am restoring a '56 Yellow Jacket hull. Dannenberg said that you would be more help. (Damn, you must be good!)

The deck is a field of mahogany stain. On it are 3 "darts" of light stain. I am concerned as to how to keep the mahog. stain from running up the adjacent grain. I had thought about doing the light first and then sealing it with a coat of varnish (someone suggested a spray over of shellac).

Another ? that I have is, should I seal the whole deck with CPES before staining, or just the light area?

John Duffy, Pass Christian, Miss."

Doing a two-toned stain on a single piece of wood, especially mahogany, is really tricky. Here's what I would do: With a very sharp and very thin blade - either a razor blade or exacto knife - and a very good, sharp straightedge, I'd cut through the veneer along the lines of demarcation between the two stain colors. You want as thin a cut as possible, and through the veneer so that it breaks the path that the stain wants to follow along the grain. Then tape one side of the cut using a masking tape that's specifically meant for masking a paint line. I think 3M makes it. Press the tape down well - you don't want any stain getting under it. Then carefully and with a very light touch, stain the exposed side. Be extremely conservative with the amount of stain - you don't want to flood it. Let it dry completely, remove the tape, tape the OTHER side, and stain that. When you apply your multiple coats of varnish, that extremely thin knife cut in the wood will hopefully fill in and become invisible - that's why you want it as straight and tiny as possible when you cut it. And most importantly - try this out on a scrap piece first. Go thru the entire process exactly as you intend to do it on your actual work, so that you find out if it works, and also so you get a feel for everything. I've been a custom cabinetmaker and have done all my own staining and finishing for over 30 years - not that that makes this process the 'right' way, but it's what I'd try. It's a tricky process, so going slow and thinking it all thru beforehand is the key. Good luck, John!

Just to add to Dan's reply:
The tape that he is refering to is called "Fine Line" and is made by 3m.
Just as it's name implies it leaves a very clean edge.
In regards to the CPES on the deck area. If you feel the need to do it apply it after the stain as it will seal the wood and not allow the stain to penetrate.
I personally would skip that part and go straight to varnish as the CPES can disturb the stain.
Would love to see pics of the process!
Karl.