I have just checked on the 1907 article by Puyo in the 'Revue de
Photographie' which is about Watkins's method of making oil prints.
Watkins produced a paper himself but as the French practicioners did not
like it they made their own oil paper . To do so they used only a thin coat
of gelatine. ....Si donc, prenant une feuille de papier, revetue sur une
de ses faces d'une couche mince de gelatine bichromatee.... They also
used double transfer paper..... En raclant les tiroirs du Photo-Club, M.
Demachy trouva quelques morceaux depareilles, et, s'etant procure un jeu
d'encres lithographiques, il encra ces papiers, de marque inconnues, le
plus aisement du monde. He goes on to say that soft inks give good
gradation and hard inks high contrast.. He also suggests that much control
can be achieved, after the print has been inked up and allowed to dry for
some days, by rubbing away those parts that need to be lightened with a
rubber(eraser), or a 'poupee en linges fin'.