There's no secret, except maybe the exact conditions each place uses. The wood is impregnated with a "monomer", the precursor to a polymer. It is called "methyl methacrylate" (MMA). In it's polymerized form it's called poly (methyl-methacrylate) or PMA. I have heard that one place uses two different monomers, but that part's a secret I believe. If MMA is polymerized all by it's lonesome into sheet form PMA, we refer to it as Plexiglas, BTW.
The wood is dried to an optimum moisture content, I believe 7% is maximum, 3% is better. It is then placed in a "bomb", or heavy vaccuum, pressure chamber and covered with the MMA. The wood is then subjected to cycles of vaccuum and pressure (and I think some heat as a consequence). The pressure's important, just like in pressure treated wood. Most of what the vaccuum does is suck air out of the pores in the wood so liquid can take it's place. Pressure forces it into the fibers of the wood. After full impregnation with the monomer, the blocks are removed and set on trays/foil where they are spritzed with an "initiator" (usually a peroxide, guys who tried this at home used Noxynol-9, the acne medicine from the pharmacy) which causes the monomer to polymerize and form large molecules called "acrylic plastics", or PMA.
To understand the difference with "home" methods: the stuff like Minwax Wood hardener and Nelsonite are typically acrylics already polymerized, ground up and then dissolved in solvents. Thus, you saturate the wood and then the solvent dries back out leaving the plastic behind. So, when you stop to think about it, if the solids content of the MW is 30%, 70% acetone and you wet the whole block inside, when it dries out only the 30% solids are left behind, so coverage can't be as thorough as with MMA impregnation.
The big difference? The home stuff "coats" the wood internally, whereas the pro procedures can essentially turn the wood into a big continous block of plastic due to the post-impregnation catalytically initiated polymerization.
Hope someone else understood that besides me. Made perfect sense as I wrote it, but I'm not sure.....
-Matt-
