I think you might find some KEY blocks or squares of codes in that still, Work small sections, using makeup soft brush and new razor blade play like you are excavating rare Dino remains, photos digi camera in place using tripod and good close up settings, Mine was similar also flatten between a couple of pc's of glass and piece it together like a puzzle, nothing liquid, no vacuums, I used a Ear bulb to poof some of the dry dirt away, you know that thing the Doc uses to Hydro- your ear drum at the Docs office,,,,Best of luck