I have discovered century eggs while living in Thailand, and instantly fell in love with these treats. Unfortunately, I haven't lived in Thailand for a few years now, and I desperately miss century eggs. It's impossible to purchase them anywhere within 1000 km radius, so I guess the only option is to make them myself.  So, I need an advice, how can I recreate this mesmerizing gift of Asian cuisine?  What have I tried so far — I have followed this recipe on Instructables, which in short was:   Made brine by combining 42g NaOH + 72g NaCL + 1L water, boiled, dissolved and let it cool down. I have used pipe drain cleaner (100% NaOH). Carefully put four chicken eggs in a glass jar, poured brine until eggs became fully submerged. Put a small glass weight on top to prevent eggs from floating. Kept them in brine for 10 days at approx 18°C. Removed eggs from brine. Found two eggs to crack, with only disfigured yolk remaining inside. Thoroughly washed two remaining intact eggs with tap water, then dried them up completely with paper towels. Tightly wrapped eggs in few layers of clear thin plastic wrap, then covered them in modeling clay shell. Kept them for 20 days this way.   After time was up, I opened them, to find out to my own disappointment that my experiment had failed. The eggs were filled with a foul-smelling opalescent runny fluid about the density and viscosity of water, and the eggs themselves had shrunk away to the size of the yolk. The egg whites had stayed white, dense and opaque, and only a thin layer of it was left around the yolk. The yolks themselves were still yellow with a slight blue tint, and had overall texture of hard-boiled yolk.  Obviously, this was not the result I wanted, so I threw them away without tasting :(  Since then I have done a few more attempts, still with no luck. I have even discovered scientific papers on this matter, e.g. "Effects of alkaline concentration, temperature, and additives on the strength of alkaline-induced egg white gel.", Zhao Yan et al, doi: 10.3382/ps.2013-03596, however I was somewhat hesitant about experimenting on myself, as the paper gave no conclusions whether the provided metal salt concentrations are safe for human health with prolonged consumption.   So, can anyone point out any mistakes I've made during my attempts, or provide me with the right technique to make Century Eggs that I can follow? It is surprisingly difficult to find English recipes for these on the Internet. 
Finally - I have managed to find a reference which states that, "A less alkaline environment is needed to coagulate duck eggs than to coagulate hen eggs, which is believed to be associated with the egg white protein composition".  Since I believe the original recipe (72g salt, 42g lye)is specifically for duck eggs, it would explain why you are experiencing difficulties, and why my result is not quite what I expected to see if the brine for "chicken" eggs needs to be more alkaline.   For my next few attempts/experiments I am going to incrementally increase the lye.  Improving the Safety and Quality of Eggs and Egg Products: Volume 1: Egg chemistry, production and consumption Ed. Y. Nys, M. Bain, F.v. Immserseel Section 21.5.2 Pidan 