Snagged this off ebay today...figured it was worth a gamble, saw marks seemed like a good indicator to me as well as the possibly whiteish dried slurry so made an offer and they swapped it to bin for me, description is this:
VINTAGE VINTAGE RAZOR ,KNIFE, TOOL SHARPENING HONE 14" x 1" x 1 5/8".NO CHIPS ,GREY IN COLOR VERY SMOOTH
Attachment 172723
Attachment 172724
Attachment 172725