After leaving behind photography in the mid-1850s, Le Secq contacted Nègre in 1875, expressing his intentions to publish certain of his photographic series including his photographs of Chartres as reproductions in ink – par les encres grasses. His renewed interest constituted Le Secq’s final effort to permanently archive his work for the missions héliographique. By the 1870s, Nègre was producing less and less. Photomechanical printing had not make great strides since the late 1850s. Opting for the practicality of a more current form of photolithography patented by Thiel Aîné et Cie of Paris, called the Pantotypie, Le Secq published his portfolio of his Chartres photographs made more than twenty years prior.
Pantotypie appears to be a Collotype variant. In the description Thiel credits Poitevin’s use of bichromate and gelatin. In 1869 Pinel Peschardière produced prints referred to as “pantotypie.” It is unlikely that this was the same process. 
Hanson, David A. Checklist of Photomechanical Processes and Printing, 1825-1910. , 2017. p. 136.
La Photographie. Collection Marie-Thérese et André Jammes Paris 27 October 1999 Lot 86 (salt)
Fragments d’architecture et sculpture de la Cathédrale de Chartres / / d’après les clichés de Mr. Le Secq, artiste peintre ; et imprimés à l’encre grosse par Thiel âiné et Cie Editeurs à Bruxelles : Aug. Vandermolen ; Dépot à Paris : Chez Mrs. Thiel âiné et Cie, [1880?] 1] leaf,  leaves of plates : chiefly ill. ; 57 cm.
 Hanson, David A. Checklist of Photomechanical Processes and Printing, 1825-1910. , 2017. p. 136.
Buerger, Janet E. Le Secq’s "Monuments" and the Chartres Cathedral Portfolio. Journal of Photography ( Vol 23, No. 1, June 1980)
Janis and Sartre, Henri Le Secq Photographie de 1850 a 1860