The photo is a bit blurry to see the bleed but I know what you are talking about. I don't think you will ever get a full seal with shellac in the ply substrate. The cracks from the thick rotary veneer are just too big. I think you could change how you apply the black though. Still apply the shellac sealer but then try to spray a very dry coat of black. It is not easy with cans an air brush would be better. Many dry coats to get full colour.

I came out to the shop the morning and got a better photo.

BH

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My only thought would be to not use the can shellac. Mix your own from de waxed flakes to get a thicker consistency. Might fill the pores/seal faster than flooding with the thin can stuff.

Use a black paint that is comprised more of pigments and not dyes. It's the dyes that are creeping into the grain pores.

Have you tried a black primer, then a black paint?

Do you think the paint might be getting between the prefinished film layer and the plywood? Maybe that finish is brittle or not bonded well?

Good thoughts. I'll see what I can find for a base coat that doesn't affect the Oramask adhesive.

I've completed the current group so this won't happen for several months now. The double coat of rolled on full strength shellac improved the situation dramatically but not 100%.

Thanks for the ideas everyone. This has been a strange problem.

BH Davis

I've been finishing my local brewery's (Caldera Brewery Ashland Or.) wood tap handles for at least the last 10 years. At first we were using Ash cuts from Sawyer's oars until we needed more than they could provide so we started using Maple when the ash ran out.
The process we ran was;
Woodworker makes the handle
I finish with 3 coats of 2k WB poly
Then the engraver takes over; masking, laser engraving, painting black on the engraved surface.
On the first run with the maple the black paint looked to be weeping up under the masking but in reality one of the local wood turners pointed that the paint was being drawn up in tiny voids or straws that are present in maple. So we quit using the maple and went back to ash, problem solved.

Thanks Nick. That is very interesting.
BH Davis

I would try spraying a sanding sealer first. Or mist the black on with a primer first. You would need something that sprays better than a can to mist it. You could also try a water based, clear, grain filler. I also wonder if thinned down hide glue would seal the grain.

Interesting that maple drew in the paint worse than ash. I guess this is the power of capillary action. I presumed the larger the pore the worde the problem but it seems the opposite is true.
The only time I did black engraved graphics in wood was for a dining table. I v carved the female and cut the infill from Colorcore Formica. Then I painstakingly spread pva with a toothpick and pressed each formica letter in place. The outcome was good but I only did it once for a reason.

I doubt the maple is absorbing the color. It is most likely a poplar cross band below the maple that is absorbing it. Not knowing the plywood type, the poplar is a guess at best. With my suggestion on sealing it with hide glue- Id probably do a quick sample of mixing hide glue and then titebond, both thinned, on a flat surface, and see how well the paint sticks to both. I would lean toward using thinned hide over titebond but dont have a solid reason for that. I do think bw the glue, sanding sealer, or a thinned spray coat of primer, you will get it figured out.