Wedgewood and Davy's experiments with photography (like so many others at that time) would fade quickly with exposure to light. They were not fixed/stopped/permanent. Niepce and Daguerre made permanent photographs in 1826 and 1835. Niepce's first "fixed" photo lacks detail. Daguerre's Daguerreotypes are small one-of-a-kind works on metal. Soon after, Talbot's calotype produced a negative, from which many prints could be made. From that point forward, photography quickly advanced in both resolution, permanence, and ease of production. I argue that resolution (grain size, pixel size) and ease of production have superseded permanence.
Daguerreotypes last as long as the metal does not corrode. Photogravure prints last as long as any other intaglio print can last. Intaglio printmaking is proven to last for hundreds of years if created and cared for correctly. Daguerreotypes are not yet proven to the same degree as intaglio prints, but the daguerreotype process was developed a few hundred years after intaglio printmaking (and I readily accept the argument of daguerreotype enthusiasts who claim the plates can last as long as an intaglio print).
I recently helped clean up after a flood at my family's house. Fortunately, the flood was caught within 24 hours, so photographs did not have any extended time in water. The clean up prompted me to think about the subject of permanence, and how it seems to be increasingly ignored by the popular photographic world. The flood short circuited an electric circuit. If a computer was connected to that circuit, the information on the hard drive could easily have been corrupted beyond recovery. Digital photographs could have all vanished at the same time. The smallest amount of water that reached inkjet and laser prints immediately damaged the photographs. Even the photos made by "professional" inkjet printers were effected. The photos produced by a professional photo lab, most likely on a modern inkjet style printer, faired better, but indicated that they would not have lasted more than the 24 hours. The only damage to chemically developed photographs was some wrinkling and an occasional piece of cheap backing, postcard, or other paper that had stuck to the image surface, gluing the two parts together. Otherwise, the chemically developed (or "wet darkroom" developed) photos are in very good shape.
The modern inkjet prints, which faded and bled with minimal exposure to water, seem as impermanent as the early Wedgewood and Davy prints that faded in the sun.
Additionally, three intaglio prints were soaked in the flood. The frames and mats were ruined, but he prints are fine. The only threat to the intaglio prints on cotton paper would have been mold. But, mold would have taken a week to start developing on those expertly crafted prints.
I have colleagues and friends who have been through similar flood events. None of them were as fortunate as my family was. Most of them had running water for several days (or weeks). Some of them had to contend with rising sea or river water that mixed other chemistry and abrasives into the flood, speeding the damage. It only strengthens my resolve to keep making intaglio prints. They won't survive flooding rivers, storm tides, or the abrasive effects of excessively turbid water. But, intaglio prints have a better chance at survival than most other methods of photographic reproduction.
Of course, I must consider ease of production and resolution. Photogravures are difficult to make. Even the polymer plates that I am using, while easier to produce than traditional copper plates, are still finicky and time consuming. Additionally, any color must be painstakingly introduced, and really amount to split toning, or spot toning (though it can be quite beautiful). Resolution of the digital world has passed what I can do with photogravure. It is catching up to the largest analogue negatives (if it hasn't passed it already). So, if I need a large image, in color, I do not have any other choice but to use my digital processes to produce either a high quality inkjet print (faster, less expensive option) or send the digital file to a lab, who then makes an internegative to use in the creation of a wet darkroom color print. I could make color gum prints of a certain size (and want to), but I have not even begun to learn that process.
This is an informal blog, so I will sum up by saying that recent events have forced me to seriously consider which images are most precious to me; which stories I want to preserve through the intaglio process; what I can do to spread those stories around.
update (April 16, 2015):
I was happy to have the following article forwarded to me. It seems that the Royal Photographic Society and Photo Marketing Association are thinking along similar lines as me.
update (July 19, 2015):
Found this article about bit rot by Michael Ernest Sweet and how a real print will last longer than all of that digital data.