(I'm assuming the posting of links is allowed
Sure, no problem!
As said, I'm not familiar with the term 'red oxide print', so I don't really know what it is.
If it turns out to be a carbon print, then I can answer your other questions - but keep in mind that this is in the assumption that it's indeed some kind of carbon print, and not an entirely different printing process that is being referred to.
How does a carbon transfer print work then and what is it made from, an original negative?
Yes, a carbon print was historically typically made from a regular B&W negative. It's a contact printing process, so that means the negative needs to be the same size of the negative. The hardening action was typically through the use of dichromate, which hardens a pigmented gelatin matrix under influence of exposure to UV. It's a slow hardening action, which is the reason why it's a contact print process. Once hardened, the image needs to be 'developed' by washing away the unhardened gelatin, leaving the image, consisting of a hardened gelatin layer. In this step, the image must at the same time be transferred to a support; this is where the mirroring happens. The transfer is a mechanical necessity as otherwise the image would wash away together with the unhardened gelatin.
There's a related 'carbro' process that used an interaction between silver, chromium and gelatin to harden the gelatin. In this case, an enlargement could be used to make a print from, so the original negative could be smaller than the final print. This process relied on enlarging papers with no or a very soft supercoat; it doesn't work anymore with modern enlarging papers. Physically, a carbro print is very difficult or even impossible to distinguish from a carbon print, so they can be considered as practically the same from an archival and collectionist viewpoint.
I'm assuming the image reversal isn't normally an issue except as here, where there was a printed banner of some sort in frame?
Yes, indeed. There are variants of the carbon transfer process that add another transfer step so the image is mirrored again, making it end up correctly oriented.
And what does it allow compared to a traditional print process? Is it just for colouration of the final print?
The carbon transfer process was one of the earliest printing processes that could produce any hue, since the colorant is a pigment, and in principle any pigment can be used. It also allows a full tonal scale with very good dmax, the prints are very stable and practically do not deteriorate as long as they're not subject to excessive moisture, and any number of prints can be made from a single negative. Most carbon prints tend to be monochrome, often with some degree of warm toning depending on the carbon pigment used since carbon has historically been the most-used pigment for the process (hence the name, 'carbon' transfer). In the late 19th and early 20th century there was a bit of an industry that made ready-to-go carbon tissue: the pigmented gelatin layer that could then be sensitized with dichromate and used for printing. Interestingly, I recall having read that this could come in different colors, so not just black. I recall e.g. a dark blue/green variant being offered, and quite possibly (but I'm not sure about that) an iron oxide red one as well. Either way, an iron oxide red/brown tissue is easy to make; in fact, Calvin Grier routinely does this as he uses red iron oxide for the skin tones of his full-color carbon prints.
Coming back to your original questions:
1) Is there any truth to that assertion, and if not, whats the real story..?
2) Are there any special measures he should take to ensure long term preservation of what are clearly already old prints?
1: If (again,
if) this is indeed a variant of the carbon printing process, then no, this publisher was certainly not the first or only party to do this. The carbon process originates in the mid-19th century and was pretty much 'ripe' and used in full swing by the end of the 19th century. That period was actually the heyday of historical carbon transfer.
2: Again, the same if: carbon prints are robust in themselves, but are subject to deterioration of mostly the paper base and the gelatin. Neither withstand moisture very well, but prolonged storage in excessively dry conditions can likewise crack the gelatin matrix. Storage conditions suitable for silver gelatin prints will also be fine for carbon prints. The gelatin can furthermore yellow; I'm not sure if this process can be halted and how far it'll proceed, but I expect that exposure to (UV) light will likely accelerate it. However, other than that, carbon prints are generally light-fast as long as a light-fast pigment is used, and red iron oxide certainly falls in this category. So the prints should be more stable than e.g. silver gelatins.
the photogravure process (which fits the time period) uses red oxide but of course produces black and white print....however it is a much cheaper process for the production of handbills and the like, so I have two questions....firstly does photogravure result in a reversed image (which would explain the reverse text) and secondly, was there a commonly used secondary chemical process in the 19th century that would result in a red print such as this one? Or even perhaps something that might degrade from BnW to red over a period of 150+ years
Good questions; whatever I can come up with is likely incomplete, but let's give it a shot.
Photogravure is a possibility, but would be easy to tell apart from a carbon print. A carbon print is a gelatin matrix with pigment in it. So you'll see the slick, hard and somewhat glossy surface of the gelatin. If the prints are dead matte and do not lay on top of the paper base, then it cannot be a carbon print. Given the appearance of the image in your first post, which appears to be a glossy print that's also somewhat brittle, this suggests a gelatin layer on top of paper. That's not consistent with photogravure and one of the reasons why I initially suggested a form of carbon transfer.
Photogravure can, like carbon transfer, occur in any color since this really only depends on the pigment used, and pretty much any pigment can be used in a printing ink. Photogravure might be recognizable along the edges of the image where you see signs of the edges of the plate, see signs of inked scratches in the plate surface, etc. More importantly, photogravure is a halftone process, so it's not continuous tone. With a magnifier, you should see little dots of ink. If you see continuous tone, it's not photogravure. Contrary to what you state, photogravure was not just used for low-end printing; it was used for high-end photographic reproduction. A notable example is Stieglitz' Camera Work editions, which used the process to reproduce the original photos. These were (still are) considered as excellent. The same is true for some of the (early) volumes of Curtis' The American Indian (the later volumes were also photogravure printed, but the prints were much poorer in quality than in the early volumes).
As to other processes - the world is a big place! For sure, there are possibilities, but again, the appearance of the first print which to me looks like some kind of gelatin imaging layer, limits the options a bit. There's still the hypothetical possibility that these were some form of metal-based process and the prints were then supercoated with gelatin - but I really doubt anyone would have gone to those lengths. So if the paper has a gelatin layer (or another colloid with similar appearance), it's probably safe to assume that the gelatin is essential in the image-making/printing process. That means the options are reduced to a much shorter list:
* Albumen prints were very common back in the 19th century and early 20th century. They were difficult to process properly and the often fade and yellow. A faded albumen print can very well have a reddish hue. In a collection of albumen prints made over an extended period of time, I would expect to see large variation in the degree of fading and yellowing. Moreover, I would expect to see variations within a single print (e.g. edges faded more than the center). If all prints look similar and they are of even hue across the surface, I think albumen is an unlikely candidate.
* Silver gelatin prints, toned to a red hue in some way. Some kind of metal replacement toning could result in these reddish hues. I'm not aware of any toning process that uses red iron oxide, however, so that would make the name attributed to it a little puzzling. It could still refer to the hue, and not the technical nature of the process.
* Carbon transfer as discussed above.
* Gum bichromate; although typically these would have a more 'painterly' look and the tonal scale is really not consistent with how I'd expect gum prints from that era to look. So I think we can set this one aside.
I might be forgetting a few.
If you want to know for sure what these are, my suggestion would be to get in touch with a photo museum that's accessible to you and ask if one of their archivists or restorers would have a look at one or a few samples. They should be able to narrow down the options considerably by just looking at them (with the aid of a microscope here and there). If I had physical access to these prints, I'd start by having a look at them with a good magnifier and take note of the image structure, as well as study the substrate and surface to narrow down options.
It's an interesting puzzle, for sure. Whatever else the owner can tell you would be of great use as well.
