To my understanding, it was more of a study on Peroxide than an opinion -
https://www.ncbi.nlm.nih.gov/pubmed/1906612
After reading this, and other sites, the batch of eggs that I have in now were sprayed down with peroxide at 3%, and allowed to dry, as part of their 'resting' process before they went in the incubator. I did not clean them, though, just sprayed them and let the peroxide dry on the shell.
They went in on the 1st. On the 6th, I opened the incubator to turn them for the first time that morning, and got hit in the face with a rancid odor. It was tracked to one egg, not leaking, but olfactorily bad. I had another sniffer in to confirm that, since I couldn't see anything wrong inside it, though I did notice that the shell had visibly paled. It went from creamy beige to grey-white. It did not smell like rotten egg, no sulfur smell at all. It smelled like rancid, decaying, putrid, rotting meat.
That egg was removed, and an examination showed albumen and yolk normal looking, but a drop or two worth of reddish-brown slime inside. All of which got flushed down the toilet. I'm assuming that was bacteria, and that it was inside the egg when it was laid, since that was actually a CLEAN egg out of a batch of very dirty ones.
Of the rest, though it's too early to be really certain, out of the remaining 21 eggs:
13 show signs of development
1 shows signs of development, but also what could be a blood ring. I'm puzzled by the combination - possible blood ring and possible veins.
7 were completely clear at last check. One of those seven has a crack at the narrow end, which I covered with scotch tape.
Original count was 22 eggs which I received via the mail, purchased from
eBay.
I plan to candle again on the 11th, and remove any that continue to look clear. Since removing the rancid egg, there's been no foul odor at all. All of the eggs, regardless of having poop stains on them, smell like eggs and not poop. I never knew before my previous (1st) effort at incubating that raw intact eggs had a smell. It's not unpleasant! But now I will always think of it as 'egg'.
My first batch of eggs were 18, of which 11 showed some sign of development, 4 hatched. Technically, my progress is higher at this point, at 63% (rounded down) showing at least some indication of life, as opposed to 56% (rounded up) last time.