Black inlay in copper alloy sign

Recently a student brought in an early twentieth century "brass"
plaque that used to hang in front of her grandparents' store in
northern NY state.  There are losses to the black inlay in the
incised letters.  I used to know what this black material is but I
am having a brain freeze.  The material is grout-like in
consistency, very hard, greyish black with a slight tendency to
flake.  The depth is about 5mm.  Can anyone help identify the
material and suggest an appropriate fill material should she decide
to fill the losses?  The plaque will remain indoors from now on.

Fiona Graham, MAC, CAPC, CAHP
27 Livingston Avenue
Kingston ON K7L 4L1
613-547-2396
Mobile: 416-912-3781


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                  Conservation DistList Instance 29:40
                   Distributed: Sunday, March 6, 2016
                       Message Id: cdl-29-40-021
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