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I fear I've painted myself into a corner and hope someone can suggest a way out.

I've built and carved a mahogany neck and attached a bound fretboard (ebony binding with maple lam) and an ebony headplate over a maple veneer. It's now shaped and sanded and ready to finish.

My plan was to ebonize the neck using a wash of quebracho bark tea followed by vinegar/steelwool tea, finishing up with a conventional finish. It works very well on test pieces of mahogany. What does NOT WORK AT ALL on test pieces is any way I've found to prevent the ebonizing teas from ebonizing the 0.020" maple line that runs along both sides of the fretboard and around the headstock. I've tried masking tape (maybe not the right kind) and my challenge in following the line was overwhelmed by seepage of ebonizing liquid under the edge of the tape.

Plan B is to ebonize everything. (Plan C is to forget ebonizing and finish the neck conventionally.)

Any suggestion on how to pursue Plan A would be very welcome.

Have you tried shellac?

That's so crazy it just might work!

Is your maple veneer right up against the mahogany, or is there another veneer layer (black for example) between it and the mahogany? If it's right up against the mahogany, that will be more challenging.

The shellac suggestion may work. Also, if by any chance you are going to use epoxy to pore fill the mahogany, it can be used to protect the veneer. I stained a mahogany neck to match a rosewood body and it had a 0.020 white veneer under the head plate with a 0.020 black veneer between the white and the mahogany. Masked off the mahogany, applied the epoxy to the veneer edge, then masked over the veneer and applied stain to the mahogany. In the few places where there was a tiny bit of seepage under the edge of the tape, the stain came off the epoxy on the veneer easily using a razor blade as a scraper.

You asked about tape. I've found that the green FrogTape painter's tape does a very good job of sealing. Quite a bit better than the usual blue painter's tape.

_________________
Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

With a small brush, run 2 coats of shellac down the maple - won't matter if some gets on the ebony. After your ebonizing, scrape the shellac off the maple on the fretboard. For the head, scrape the shellac off the mahogany before ebonizing, then off the maple after. I have used a fresh razor knife blade with blue tape over the sharp part except for just the right amount of bare blade sticking out the end.

Here is a pro at Northwoods with more than you need to know for now

https://www.youtube.com/watch?v=TNbsZsSabPs

Pictures through the process and when you are done please

Ed

Thanks for the input. As suggested, I painted two coats of shellac on the edge of the fretboard and headplate, trying to cover the edge of the maple layer without getting (too much) shellac on the mahogany neck. Then I scraped the mahogany neck with a razor blade up to (as best I could) the edge of the maple layer. Today, also as suggested, I masked the shellacked surface using Frog Tape and applied the ebonizing solutions. They work almost immediately, so I now have results.

The efforts to protect the maple from ebonizing were mostly successful. Only about 5% of the maple was discolored (turning black or grey). But out of ~60" of binding there are around 3" (in sections ranging from 0.05" long to maybe 0.25" long) that required scraping, and some still didn't come clean. (The ebonizing fluids revealed the layered, fibrous structure of the maple lam on the ebony binding and the end grain of the maple on the headplate veneer.) Scraping was challenging because as the blade touched the mahogany it removed the ebonizing, leaving a thin brown line.

So now I have a neck that looks quite nice from a distance or with casual handling -- but I know better. I have friends who build custom cars; this would be described as a 10/10 solution -- looks great from 10 feet away at 10 mph. I'm hoping that applying the final finish will elevate the neck to a 5/5 solution.

But it is good enough that I've abandoned thoughts of Plan B (and it's clearly too late for Plan C).

Of course, what the Utoob vid shows is celluloid or other plastic.
Don't know how many times I've said it, but THIMK. Plan way ahead...for everything. If you want to dye an instrument, you must either not use wood binding/purfling or seal it off extremely well. I used to painstakingly apply 3 coats of lacquer by hand over purflings. Two coats of thin shelIac won't do it. I always used celluloid for bindings. Maple bindings and the like are mostly for those "clear" finishes. Bindings and purflings on guitars to be dyed should have a black or B/W/B purfling line next to the wood to be dyed.
Scraping the lacquer off of a rosette after tinting a top...

^^^^

This.

I have learned that EITHER I do a natural finish with wood binding/purfling OR a burst with plastic binding and purfling.

I am sure there is some Jedi master who can pull off both, but I’ve learned my limitations.


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Here is a little variation you may be able to use. B/WB or B/W or black purfling can be plastic or wood. By choosing either/or, you may just become that Jedi master.
Note the photo above, the B/W/B rings are plastic and the center purfling is wood. The same can be done on the binding say, where the side purfling might be plastic and the binding wood. This gives you more options. There are a lot of ways to tackle a problem and thinking things through from beginning to end ensures you a good outcome. Then all you have to do is figure what glue goes where...