I am a bit surprised and taken back by the lack of responses or expressed interest regarding this thread. I thought a solution to the problems that exist when introducing natural wood into an aquarium would excite just about everyone here. If a coating could provide a nontoxic seal and where the sealant is bonded somewhat to the material but to the greatest extent itself, the subject piece (driftwood in this case) would be rendered airtight and waterproof. This would, in turn, render a number of related inherent problems as non-issues. There wouldn’t be any tannin discolorations or
PH effects, the piece would retain its original dimensions and its longevity would be greatly extended. There are a number of beautiful woods around. Even if you’re into colored rocks and animated decorations, get yourself some purple heart or red cedar. You would not be limited to buying expensive exotic imports from some foreign country unless that's what you want. You could now look for your treasure on any area lake or field, which is exactly what I did. The only remaining problem is buoyancy and aquarists experience that problem with all but the most dense hardwoods. Periodic maintenance (removal, inspection, cleaning, recoats) is a given.
I’m off my soapbox now and was going to pass on some discourse (paraphrased) from one of the manufactures of “Poly-Varnish Paint”:
Question:
I have a piece of driftwood that will be used in an aquarium. An article... makes reference to a product called "polyurethane varnish paint". I'm not a chemist but these terms sound conflicting to me. Could you tell me about your product, whether it would hold up underwater and if it's toxic to fish…
Reply:
'Polyurethane Varnish Paint' is just a reference to the fact that varnish is manufactured in the same way as paint and our Poly varnish is made on the same solvent/resin basis as our paint. Polyurethane varnish is waterproof when dry but does have a slight yellow tinge, not a water white varnish. All Humbrol paints are made to EN 71 standards.
Question:
What about an application where it is to be used under water? Does this "paint" form a solid barrier (given adequate number of coats) so that it is watertight? Does it emit any chemicals as it "weathers"?
Reply:
When fully dry there should no problem under water and the wood will be sealed allowing the wood to be dry. When dry the varnish does not release any form of chemicals, it is also compliant to EN 71 which is the Toys Safety Regulations that state that the paints contain no toxic metals.
If anyone here can, please blow holes in this product because if I check some other reference material (ie. Safety data sheets) and it holds true, my next step would be to conduct a trial. In this trial I would probably use as large a piece I could stuff into the smallest tank I have, dump in some fairly fragile inexpensive fish and start monitoring water levels and observe the fish for signs of stress.