Different creatures. That article used a multifunctional polyaziridine crosslinker. That chemical indescriminately crosslinks free hyroxyl groups IN SOLUTION. Of all the available azyridine (or related crosslinking agents) that I've been able to find (and I have checked with most of the suppliers), once mixed, you will have a maximum pot life of 100 hours. These things are designed to be used in two part coatings, to be combined just before application. I have actually gotten a hold of several different samples, and can not make it last more than a few hours when mixed with any useful concentration of shellac. I believe that shellac hardeners that will have at least as long a shelf life as the shellac itself, need to be something that crosslinks when dry. As far as I can tell, other than the well known naturally occurring resins (like sandrac and copal), you need to use a liquid, non-hydrophylic (oil soluble), plastic monomer (like a vinyl). These are known to crosslink with shellac (and other finishes) over time when dry. They do not react well in solution, giving mixtures like that a rather long pot/shelf life.
Other studies, in which shellac has been made more resistant to degradation by solvents, the pH or other variable of the solution has been altered. These have proved successful in many cases, but they ALWAYS seem to make the shellac softer when dried. I don't need a finish that resists alcohols and acids, but becomes dented from resting on a table. That works fine for pill coatings (most of this research is done for the pharma industry), but not so much for finishing my wood turnings.
As for the stuff I've been using, which works very very well, the only place from where it can be purchased as far as I know is from The Wood Works, in Australia. Here is the link:
http://www.thewoodworks.com.au/shop...-to-formulate-hard-shellac-for-500ml?vmcchk=1
Price is actually very reasonable. I usually buy 2 at a time to save on the shipping and international transaction fees. Each container is a 500 ml plastic bottle with about 50 ml of hardener additive. You add shellac to fill the bottle, shake it up and let it sit for 72 hours, then use it as you would any shellac.It will last almost indefinitely until mixed with shellac, after which it has a stated shelf life of up to 18 months. I have mixed some up that has lasted me over a year. I start to get nervous with any shellac-based finish after that time, and simply discard any that I've mixed up longer ago than that.