Philippe has put the image in question on his website and here is the link:
It is 16x20cm, it is made by the Sury Color process from 1924, and Philippe says it is "not a gum print but one made with his color paper, invented and patented in 1924" (which patent Philippe has). He manufactured a color paper and sold it at that time, much like the other papers on the market I suppose like Artigue and Hochheimer, etc. and like Artigue the process was kept secret, but apparently Philippe has written about this in his book on Sury.
Philippe, est-que ce papier une mixture des colloids, comme gelatine et albumine? Ou pas des colloids dans son formule?
All but one of the direct carbon papers I have come across were made with mixtures of colloids or straight gelatin, in other words, not straight gum prints per se although gum was in some of them. The one that was pure gum, the J. Page Croft paper, was hardened by methylated spirits of alcohol and a tad of sulfuric acid in the coating mix. I don't know if he was successful in his paper endeavour, as I don't know how long he manufactured the paper, but obviously the ones with mixed colloids have lasted because Fresson is still around.
I find it interesting that acids and methylated alcohol create less solubility in gum...something to be tested. When I tested acids (lemon juice) it created more stain in the highlights.
Enough for now...and please excuse the translating back and forth--but I felt that the Sury stuff is very interesting alt info to put in your pipe and smoke for the new year ;0