A very productive couple of days in the darkroom with some results I'm quite pleased with. These prints are still wet, just out of the wash. The photos of them here are poor, taken with my antiquated smart phone. In case you are wondering what these prints are, they are part of the series (l,b)≃(209°, -57°) GC. They are 'silver gelatine prints', printed on 'fibre-based' photographic paper.
The term silver gelatin silver print (or silver print), refers to all black and white prints that have been produced in a wet darkroom. All traditional photographic materials that are light sensitive, both photo paper and film, contain silver. A thin layer of light sensitive silver salts (silver nitrate), is suspended in a gelatin coating on the surface of the paper. The silver salts continue to be light sensitive until the paper (or film) has been developed and fixed. What remains is a black and white image. The black in the print is the silver that has reacted to light. The white part of the print is the underlying paper which has emerged in areas of the image where no light has hit the paper. Silver salts in the unexposed parts are washed away in the development process. When working in the darkroom, one is literally working with light and shadows. Negatives simply cast a shadow onto the photo paper, which result in a positive image.
'Fiber-based paper' is a pulpy, heavy paper that can withstand chemical processing and washing. It is the same kind of paper that was commonly used up until the 1970's for most photographic prints, and is quite archivally stable when properly processed and washed. From the late 60's onward, prints began appearing on 'resin coated' or 'RC' paper. This paper is essentially a thin sheet of plastic. The advantage of RC paper is that the processing times are much shorter, and since plastic is a non-porous material, washing times are a fraction of fiber paper.
Your family may have photographic portraits of relatives from the 1930's or 40's that still look quite good. They have persevered because they were printed on an archivally sound fiber-based paper, were properly processed and washed, and your family has done a good job caring for the print. As I would like my work to be around as long as I can possibly make it last, I try to implement archival best practices where I can. Many photo-artists don't have a clue, and rely upon a lab to do all their printing. The problem with this, is that the customer of the lab has no control over the chemistry used in the processing of the print. Some labs, particularly those with lower prices, (attractive to artists), will squeeze out as much as they can out of their chemistry and potentially let some of their chemistry exhaust before changing. Prints processed with poor chemistry, or that have not been properly washed, will initially look fine, but over time (a couple of years), will deteriorate. I've learned this the hard way with lab processed work.
There are of course pigment ink prints, but this technology has been around for less than 20 years. Pigment inks are purported to be archival, but time will tell. Archivally processed, fiber- based silver prints on the other hand have a proven longevity.
During a session in the darkroom, I ensure that I am working with fresh chemistry, use a two step fix, clear the fix with a hypo clear, wash in a proper archival washer, then tone or stabilize the print. A full, thorough wash of the fibre print is extremely important as the processing chemistry will saturate the absorbent fibres. Chemical residue left in the paper will form stains and destroy the print over time. The chemistry must be fully extracted to be archivally sound. Working with fibre based paper and following a rigorous archival regimen is extra work and expense, but worth it for the peace of mind that these prints will last a long long time. When properly cared for, these prints will at a minimum outlive your great great grandchildren.